ALBERT

Notes: Soils represent a major sink for organic xenobiotic contaminants in the environment. The degree to which organic chemicals are retained within the soil is controlled by soil properties, such as organic matter, and the physico-chemical properties of the contaminant. Chemicals which display hydrophobic and lipophilic characteristics, as well as a recalcitrant chemical structure, will be retained within the soil, and depending on the ‘strength’ of the association may persist for long periods of time. This review describes the behaviour of hydrophobic organic contaminants in soils, focusing on the mechanisms controlling interactions between soil and contaminants. The bioavailability of contaminants in soil is also discussed, particularly in relation to contact time with the soil. It considers the degradation of organic contaminants in soil and the mechanisms microbes use to access contaminants. Finally, the review discusses the ‘pros’ and ‘cons’ of chemical and biological techniques available for assessing bioavailability of hydrophobic organic chemicals in soils, highlighting the need to quantify bioavailability by chemical techniques. It concludes by highlighting the need for understanding the interactions between the soil, contaminants and biota which is crucial to understanding the bioavailability of contaminants in soils.

Notes: Multivariate methods have been widely used for revealing the structures of communities, and in this paper we explore one particular method, namely correspondence analysis (also called reciprocal averaging), for studying humus profiles by the ‘method of small volumes’. The present study was done on humus profiles under holm oak (Quercus rotundifolia), an evergreen Mediterranean species, in the High Atlas of Morocco. Three sites (1500 m, 1700 m, 1900 m altitude) and 2 years (1999 and 2002) were compared. The humus form is Dysmull (mull with thick litter horizons), with variations in the thickness of the OL (entire leaves), OF (fragmented leaves with faecal pellets) and A (hemorganic) horizons according to altitude and year. The dead leaves are rapidly incorporated into holorganic (earthworm, insect) and hemorganic (enchytraeid) animal faeces, which form the bulk of the OF and A horizons. The S horizon (weathering parent rock) shows the greatest development of the root system. As altitude increases more fresh litter (OL) or more humified organic matter (OF, A) is accumulated. Variation from year to year is depicted by opposite differences in the amount of entire oak leaves and of dead roots. Humus components (classes) are used as active (main) variables, after standardization of their means and variances. The addition of numerous passive (additional) variables, standardized in the same way as active variables, enabled us to understand the influence of biological and climatic effects on the composition of humus profiles and soil trophic networks.

Notes: Microbial ecology is the key to understanding the function of biodiversity for organic matter cycling in the soil. We have investigated the impacts of farmyard manure added over 120 years on organic matter content, enzyme activities, total microbial biomass and structure of microbial populations in several particle-size fractions of a Luvic Phaeozem a few kilometres northeast of Halle, Germany. We compared two treatments: no fertilization (control) and 12 t farmyard manure (FYM) ha−1 year−1 since 1878. The fine fractions contained most C and N, microbial biomass, total amount of phospholipid fatty acids (PLFAs) and greatest invertase activity. Xylanase activity as well as fungal biomass increased only gradually with diminishing particle size, whereas the relative abundance of fungi decreased with diminishing particle size. The least diversity of the soil microbial community, indicated by the smallest Shannon index based on the abundance and amount of different PLFAs and small number of terminal restriction fragments (T-RFs) of 16S rRNA genes, was in the sand fractions. The results supported the hypothesis that this microhabitat is colonized by a less complex bacterial community than the silt and clay fractions. Addition of FYM had enhanced the amount of organic matter, total microbial biomass, and xylanase and invertase activity, and induced a shift of the microbial community towards a more bacteria-dominated community in the coarse sand fraction. Microbial communities in finer fractions were less affected by addition of FYM.

Notes: Predicting the rate at which rain infiltrates on steep slopes is very uncertain. There is no consistent information in the literature. We have therefore related infiltrability to slope gradient under field conditions by experimenting on a gravelly loamy soil occupying the upper half of a cultivated convex hill in northern Thailand. Fifteen 1 m × 1 m plots with slope gradients ranging from 16 to 63% were established, and simulated rain was allowed to fall on them at controlled rates and for fixed times. We obtained the following results. The surface fell 0.4–7.2 mm due to compaction and soil loss. The proportions of crust (0–40%) and embedded gravel (10–60%), the runoff coefficient (0.05–0.78 mm mm−1), the mean sediment concentrations (0–5.6 g l−1), and soil detachment (10–313 g m−2) were more pronounced on the gentle slopes than on the steep ones. The steady final infiltration rate (1–107 mm hour−1) increased sharply with increasing slope gradient. Microaggregates tended to behave like sand and become tightly packed on gentle slopes (packing crust). These results suggest that the vertical component of kinetic energy, which is greater on gentle slopes, has a dominant role. Nevertheless, the differences in compaction and in sediment concentration could not be ascribed to the vertical component of kinetic energy alone. On steep slopes the horizontal component of the kinetic energy is transformed into shear stress, hampering the development of crusts so that water can still infiltrate. On steeper slopes, the water film was thinner, thereby limiting the role of splash. We conclude that the relationship between slope gradient and infiltrability depends on the nature of the soil and must be examined in the light of surface crusting processes.

Notes: Two recent investigations have reported contradictory trends concerning the effect of image resolution on the surface fractal dimension of soil pores, evaluated via image analysis. In one case, dealing with a preferential flow pathway and an ideal fractal, image resolution had no influence on the estimated fractal dimension, whereas in the other case, involving images of soil thin sections, the surface fractal dimension decreased significantly with image resolution. In the present paper, we try to determine the extent to which these conflicting observations may have been due to the different ways in which image resolution was varied. By narrowing down (up to 400 times) the field of view on progressively smaller portions of a textbook surface fractal, the von Koch island, one causes its apparent surface fractal dimension to decrease significantly. On the other hand, changing the resolution of images of soil thin sections (up to 6 times), while keeping the magnification constant, does not lead to appreciable changes in the surface fractal dimension. These results demonstrate that there is no real conflict in earlier reports, as long as both the resolution and the magnification of images are taken into account in image-based evaluations of surface fractal dimensions of soil pores.

Notes: The sandy microdune systems of the Sahel are important for biomass production, in that they trap and store water. We have studied the movement of water over and in a dune and the chemistry of the water to understand this aspect of the systems. We experimented with simulated rain using a field sprinkling infiltrometer. We applied demineralized water with a chemical composition similar to that of the natural rain on a 1-m2 plot. The plot was delimited by a metallic two-level setting: the first enabled us to collect surface runoff, while the second measured subsurface flow. Water samples were taken at 5- to 10-minute intervals throughout each simulation for chemical analysis (alkalinity, SO42–, F–, NO3–, Ca2+, Mg2+, Na+, K+ and Si). Mass balances, combined with a simple mixture model involving one tracer (chloride) and two reservoirs (old and new waters), were calculated. The equilibrating pressures of the CO2 (pCO2) and the saturation index with respect to specified minerals (e.g. calcite, fluorite, silicates) were also calculated by the AQUA ion-pair model. The solute concentrations decrease in surface runoff as well as in subsurface water, except for F– and Si in the subsurface. The pCO2 decreased to a pressure less than the atmospheric pressure. The difference between measured concentrations and concentrations computed with the mixing model highlighted interactions between the soil and water. The dissolution of calcite which consumes CO2, and the cation exchanges, dominated, whereas the dissolutions of fluorite, silicates and gypsum appear secondary. Reactive mineral stocks were quickly exhausted, especially in the surface flow.

Notes: Rates of solute diffusion fundamentally affect the properties of flooded soils, but the effects of flooding on solute diffusion have not previously been studied in detail. Four soils with widely differing chemical and physical properties were packed to a range of bulk densities, flooded for varying times, and the self-diffusion of chloride through the soils measured. Diffusion impedance factors were derived from the results. In each soil the impedance factor decreased linearly with increase in bulk density, and between soils impedance factors increased with increasing clay content. The impedance factor decreased by up to 20% during the first 3–6 weeks following flooding, but with prolonged flooding it increased to at least its initial value. Concomitantly the cation exchange capacities of the soils increased by between 30 and 100%, there was reductive dissolution of soil iron, probably both structural iron in soil clays and iron oxyhydroxide coatings on clay surfaces, and subsequently there was re-precipitation of ferrous iron, probably as mixed carbonates and hydroxides. The decreases in diffusion impedance factors were consistent with the increases in cation exchange capacity and changes in soil iron, and the subsequent increases were consistent with re-crystallization of mixed ferrous–ferric compounds. We conclude that the effects of changes in redox on diffusion impedance will be important in some soils, although they are smaller than the effects of water content per se.

Notes: The surface composition of particles present in the fine earth (〈 2 mm) of 50 soil horizons differing in composition and pedogenetic origin (13 soil profiles) was analysed by X-ray photoelectron spectroscopy (XPS) to assess the capability and limitations of this technique and to gain better knowledge of the soil samples. The surfaces were systematically enriched in carbon, sometimes up to 1000 times, indicating that the soil particle surfaces are coated with organic substances, even in horizons where the bulk organic content is less than 0.1 g kg−1. The distribution of carbon in the various oxidation states was 0.569 ± 0.008 C[0], 0.275 ± 0.004 C[+1], 0.089 ± 0.003 C[+2] and 0.066 ± 0.002 C[+3] for most horizons (mean ± standard error, 69 data). Only Andosol surface horizons systematically had surface organic matter in a more oxidized state. After correcting the results for the presence of organic coatings, we found that Si was generally depleted and Al enriched at the surface of soil particles, while Fe was either depleted or enriched depending on the sample considered. However, the coating of the coarser soil particles by the finer ones and their differential composition explained this observation and limits the interest of XPS for characterizing the surface enrichment of inorganic elements in crude soil samples. These limitations should be considered when interpreting XPS results in future work. Nevertheless, XPS can analyse the adsorbed organic matter and its functional composition of carbon without the need for any chemical or physical extraction that might alter the structure and composition of the organic molecules.

Notes: Al hydroxide polymers (AlHO) can significantly influence the cation exchange behaviour of clays. We have determined the effect of synthesized AlHO on Ca–Na, Zn–Na and Pb–Na exchange for a series of exchanger compositions and two Al loadings at pH 6.0 and an ionic strength of 0.01 m. The preference for Ca on the siloxane surface of the clay–AlHO system (CAlHO) was greater than for the pure clay, and the average KV (Vanselow selectivity coefficient) was determined to be 2.16 and 1.24, respectively. The selectivity coefficients for the exchange reactions Zn–Na and Pb–Na were not directly determined in CAlHO systems, because heavy-metal ions bind as well to the clay surface as to the AlHO over a wide range of pH. We have estimated the effect of the presence of AlHO on the selectivity coefficients of Zn–Na and Pb–Na exchange by extrapolation of the experimental results of Ca–Na, Zn–Na and Pb–Na exchange for pure clay and Ca–Na exchange for CAlHO. The average KV was increased by the presence of the AlHO from 1.23 to 2.16 for Zn–Na exchange and from 1.59 to 2.77 for Pb–Na exchange. The increase in the preference for the divalent cations is probably caused by parallel alignment of clay platelets by sorption of AlHO. Increasing the amount of AlHO did not change the selectivity for Ca–Na exchange, and probably the structure of the system or the arrangement of the clay platelets and AlHO particles was not substantially changed. This was supported by the linear reduction of the cation exchange capacity with amount of AlHO present at pH 6.6. It seems likely that the selectivity coefficients for Ca–Na, Zn–Na and Pb–Na exchange that we found apply in naturally occurring montmorillonite–AlHO systems.

Notes: The aim was to characterize dissolved organic matter in soils under different tree species. Molecular size distribution and chemical composition of dissolved organic carbon and nitrogen were determined in water extracts from humus layers and mineral soils taken from silver birch (Betula pendula Roth.), Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) stands. Concentrations of tannins and 15 phenolic acids in the humus layers were measured. Per unit of organic matter, the concentrations of dissolved organic C and N were larger in birch and spruce humus layers than in the pine humus layer. In the underlying mineral soil, the concentrations of dissolved organic C were similar at all sites, but the concentration of dissolved organic N was greater in spruce and pine soils than in birch soil. In all soils, the 10–100 kDa fraction was the most abundant molecular size group and hydrophobic acids the most abundant chemical group of dissolved organic C. In all humus layers, hydrophobic acids and hydrophilic bases were the major components of dissolved organic N. There were only minor differences in the concentrations of total tannins in the humus layers under different tree species. Small-molecule tannins (about 〈 0.5 kDa) were most abundant in the birch humus, and large-molecule tannins in the pine humus. Coniferous humus contained more ferulic and p-coumaric acids than did the birch humus. The concentrations of 3,4 and 3,5-dihydroxybenzoic acid, vanillic acid and 4-hydroxybenzoic acid were similar in all soils.

Notes: Plant-pathogenic nematodes are a major cause of crop damage worldwide, the current chemical nematicides cause environmental damage, but alternatives such as biological control are less effective, so further understanding of the relationship between nematodes, nematicides, biological control agents and soil and rhizosphere microorganisms is needed.Microbial populations from roots of cabbage and tomato plants infested with the root-knot nematode Meloidogyne incognita were compared with those from plants where the nematode was controlled by the nematicide aldicarb, or a nematophagous fungus with biological control potential, Pochonia chlamydosporia. The total numbers of culturable bacteria and fungi in rhizosphere soil were similar in all three treatments for both plants, around 100-fold more than in control soil in which there were no plants. However, there were clear differences in the catabolic diversity, assessed by Biolog EcoPlate™ carbon substrate utilization assays, between microbial populations from unplanted soil and the rhizosphere. In cabbage, a poor host for M. incognita, the rhizosphere population from P. chlamydosporia-treated plants was distinct from the population from untreated and aldicarb-treated plants. In tomato, a host susceptible to the nematode, the catabolic diversity of populations from aldicarb- and P. chlamydosporia-treated plants was similar and differed from the untreated, nematode-infested plants. The genetic diversity of the fast-growing heterotrophic bacteria in the tomato rhizosphere, indicated by PCR fingerprinting with ERIC primers, was very different in the infested roots, whereas the profiles of isolates from both aldicarb- and P. chlamydosporia-treated roots were similar. Evidently, nematodes have a greater impact on the rhizosphere population of a susceptible host, tomato, than a poor one, cabbage, and nematode-infested roots are colonized by a different subpopulation of soil microbes from that on plants where infection is controlled, illustrating differences in root morphology and physiology.

Notes: We have developed the fractal approach to modelling variations in soil bulk density and porosity with scale of measurement or sample size. A new expression is derived for each quantity based on the pore–solid fractal (PSF) model of soil structure. This new general expression covers a range of fractal media and accommodates existing fractal models as special cases. Model outputs cover a range of scaling behaviour expressed in terms of monotonic functions, from increasing density and decreasing porosity, through constant porosity and density to decreasing density and increasing porosity with increasing scale of measurement. We demonstrate the link between this new model for the scaling of porosity and bulk density and the water retention model for the PSF. The model for scaling bulk density is fitted to data on aggregate bulk density and shown to yield good fits describing bulk density decreasing with increasing aggregate size. Porosity scaling is also inferred from the fitting of water retention data. Inferred porosities from different fittings are shown to follow decreasing, scale-invariant and increasing values with decreasing size of structural unit, and these theoretical results emphasize the need for further experimental investigation on the basic issue of density scaling in soil science.

Notes: Irrigation by surge flooding does not always wet the soils thoroughly, and we have investigated the reasons for this on an irrigated plot in northern Senegal by monitoring the water budget during a rice cropping season (100 days). The amount of water added during each irrigation event was measured, and evapotranspiration and infiltration were estimated with lysimeters and Muntz infiltration rings, respectively. At the same time, piezometric levels, neutron probe values and water tension data were recorded at two stations in the plot. These measurements showed unusual results: infiltration rate was less than 1 × 10−6 mm s−1 (less than 0.1 mm a day), there was a constant water deficit during the entire irrigation period, around 50 cm deep, and tensiometers at 40 cm reacted very slowly to water infiltration. The water fluxes in the vadose zone derived from these data showed clearly a discrepancy between fluxes calculated from hydraulic gradients and fluxes calculated from mass conservation. The hydraulic gradients suggested a zero flux plane at 40 cm below the surface, but the calculated values of the fluxes overestimated by several orders of magnitude the infiltration rates determined on the plot, whereas fluxes determined from mass conservation matched far better. These results show that air was entrapped between the shallow water table and the wetting front, and this inhibited water infiltration. Modelling water flow down the soil profile with a computer program for simulating one-dimensional water movement (Hydrus) confirmed that single-phase models cannot describe imbibition in this situation. Simple infiltration models based on a modified Green–Ampt equation accounting for air compression and air counter-flow, however, fit experimental infiltration data much better. We demonstrated that where surge flooding is associated with a shallow water table, as in many large irrigation schemes, one must take into account the presence of air to quantify the flow of water into the soil.

Notes: Incorporating straw into the ploughed layer of soil affects the dynamics of carbon and nitrogen. A precise quantification of its short-term effect in agricultural fields is difficult because biological and physical processes interact and take place simultaneously. As an alternative to experimentation, investigations have turned to simulations using mechanistic models, and we have taken this approach. The goal of our study was to test a mechanistic and one-dimensional model of transport and biotransformation (PASTIS) against a data set obtained in a field experiment in northern France. We tested carbon and nitrogen dynamics by measuring C mineralization rates, the rates of gross immobilization and mineralization of N (using 15N tracing), and inorganic pools of N in the soil profile during 1 year in a bare soil with or without addition of wheat straw. Most of the model parameters were determined in independent experiments. We estimated the biological parameters from incubation experiments in the laboratory. The simulated results were in good agreement with experimental data, particularly for gross N rates. Hypotheses concerning the pathway of microbial assimilation and the dependence of decomposition on the size of the biomass were tested. The simulated net N immobilization due to addition of straw (8000 kg dry matter ha−1) reached a maximum of 64 kg N ha−1 after 2 months, whereas the observed value was 66 kg N ha−1. The model indicated that after 13 months the incorporation of straw had reduced the net amount of nitrogen mineralized by 13% and the amount of leached nitrate by 27%. The sensitivity analysis to the depth of straw incorporation indicated that the deeper was the incorporation the less was the leaching and the mineralization of nitrogen.

Notes: Lime, mined gypsum and some gypsum-like by-products have been frequently applied to soil to counter acidity. We have examined the changes in the chemical and mineralogical properties of three acid soils resulting from the application of three industrial by-products (phosphogypsum, red gypsum and sugar foam). We did so in laboratory experiments on suspensions of soil in saturated solutions of the by-products. A sizeable fraction of the Al released by exchange with Ca of the amendments remained on the mineral surfaces as Al polymers, as suggested by changes in the CuCl2-, oxalic–oxalate- and DTPA-extractable Al contents. Polymerization of Al was promoted by corresponding neutral and basic pH of red gypsum and sugar foam saturated solutions, respectively. Sorption of these Al polymers was particularly favourable in those horizons with more clay fraction and variable-charge clay minerals. On the other hand, in most cases there was little or no detectable sorption of sulphate, thus excluding precipitation of crystalline or amorphous basic Al sulphates to alleviate Al toxicity. Based on the reduction of the Al saturation of the exchange complex in the soils, as well as on the small contents of heavy metals and natural radionuclides of the three by-products, these can be considered effective alternatives to mined gypsum and lime for alleviating soil acidity and reducing toxic concentrations of Al in agricultural, acid soils.

Notes: There is no simple and general relationship between the thermal conductivity of a soil, λ, and its volumetric water content, θ, because the porosity, n, and the thermal conductivity of the solid fraction, λs, play a major part. Experimental data including measurements of all the variables are scarce. Using a numerical modelling approach, we have shown that the microscopic arrangement of water influences the relation between λ and θ. Simulated values for n ranging from 0.4 to 0.6, λs ranging from 2 to 5 W m−1 K−1 and θ from 0.1 to 0.4 can be fitted by a simple linear formula that takes into account n, λs and θ. The results given by this formula and by the quadratic parallel (QP) model widely used in physical property studies are in satisfactory agreement with published data both for saturated rocks and for unsaturated soils. Consequently, the linear formula and the QP model can be used as practical and efficient tools to investigate the effects of water content and porosity on the thermal conductivity of the soil and hence to optimize the design of thermal in situ techniques for monitoring water content.

Notes: Use of isotope methods to measure the availability of phosphorus (P) in soils that are well supplied with P is well established. We have evaluated such methods for acid tropical soils with very small P contents, which are less well studied. The isotopically exchangeable P in soil suspensions (E value) and that in plant growth experiments (L value) were measured in soils that had received varying amounts of P fertilizer in two field experiments in Colombia. We determined the E values over 4–5 weeks of equilibration allowing for the kinetics of isotope exchange. The decrease in radioactivity in the soil solution at a particular time, t, divided by that at the start (rt/R) was described by three parameters (r1/R, r∞/R, and a coefficient n) derived from the time course of isotopic exchange over 100 minutes. Values of Et were calculated either from measured values of rt/R or those extrapolated until 12 weeks. Agrostis capillaris was grown on the same soils labelled with carrier-free 33P-orthophosphate ions to obtain L values. Agreement between E values derived from measured and extrapolated values of rt/R was satisfactory, but errors in n and r∞/R limited the precision with which we could estimate E values. For most soils, the P concentrations in the soil solution were greater than the detection limit of the malachite green method (0.9 µg l−1) but smaller than its quantification limit (3.6 µg l−1). In the soils with the least available P, the P content of the seed limited the determination of the L value. The E values were strongly correlated, but not identical, with the L values measured for the same time of isotopic exchange. We conclude that these approaches are not precise enough to detect in these soils the ability of a plant to access slowly exchangeable forms of P or to quantify the mineralization of organic P. However, these isotope techniques can be used to estimate the total fraction of added fertilizer P that remains available to the plants.

Notes: Clay–Al hydroxide polymers (CAlHO) can bind heavy metals effectively and may play an important role in the adsorption behaviour and metal binding capacity of soils. We studied the dependence of Al loading and pH on the adsorption of Zn on Na-saturated montmorillonite–Al hydroxide polymer systems. The available binding sites on Al hydroxide polymers (AlHO) had a very strong affinity for Zn ions. Zinc binding on the clay surface became important when the binding sites on the AlHO were nearly all occupied. The pH had a very strong effect on the Zn binding. At pH 6.6 much more Zn could be adsorbed to the AlHO than at pH 5.0. The effect of the Al:clay ratio on Zn binding was influenced by pH. At pH 6.6, Zn binding to the AlHO, expressed per mole AlHO, was independent of the Al:clay ratio, whereas at pH 5.0 this relation was dependent. This is related to the constant charge of the AlHO at pH 6.6, whereas at pH 5.0 the charge decreases with increasing Al:clay ratio. If clay–Al hydroxide polymers are present in the soil their Zn binding to the AlHO will strongly influence the availability of the Zn.

Notes: Aluminium (Al) is abundant in soils, but the influence of Al on the mineralization of dissolved organic carbon and thus on carbon sequestration in soil is only poorly understood. We investigated the extent and rate of mineralization of dissolved organic carbon at various Al/C ratios.Dissolved organic carbon extracted from Oi and Oa layers under coniferous and deciduous forest was incubated with initial molar Al/C ratios from 〈 0.004 to 0.44 for 130 days. Mineralization was quantified by measurement of CO2. Rapidly and slowly mineralizable pools of dissolved organic C and their decomposition rate constants and half-lives (as a measure of labile and stable C) were modelled with a double exponential equation.Increasing initial Al/C ratios up to 0.1 led to a considerable decrease in mineralization (up to 50% compared with control samples). The half-life of the stable C pool increased up to 4-fold, whereas the half-life of the labile C pool was unaffected. Ratios of Al/C 〉 0.1 did not further decrease the mineralization, but led to increasing concentrations of free Al3+ in solution, and to increasing Al/C ratios in the precipitate, indicating that the Al complexation capacity of dissolved organic C was exceeded. Decrease in mineralization as well as formation of particulate organic matter (up to 56% of initial dissolved organic C) affected mainly the stable pool. Mineralization of dissolved organic C can be predicted from UV absorption by use of exponential regressions, but adding an Al variable did not improve the prediction significantly.We conclude that Al influences substantially the biodegradability of dissolved organic C percolating into the mineral soil, which may have consequences for the carbon sequestration in the soil. Declining Al concentrations would increase the mineralization of dissolved organic C only if the Al/C ratio becomes less than the ‘threshold value’ in the range of the Al complexation capacity of the dissolved organic C.

Notes: The sequestration of carbon (C) in soil is not completely understood, and quantitative information about the amounts of organic carbon in the various fractions and their rates of turnover could improve understanding. We aimed (i) to quantify the amounts of C derived from maize at various depths in the soil in a long-term field experiment with and without fertilization using 13C/12C analysis, (ii) to model changes in the organic C, and (iii) to compare measured and modelled pools of C. The organic C derived from the maize was measured in soil samples collected to a depth of 65 cm from four plots, two of which had been under continuous maize and two under continuous rye during long-term field experiments with NPK and without fertilization. The fractionation procedures included particle-size fractionation and extractions in water and in pyrophosphate solution. We used the Rothamsted Carbon Model to model the dynamics of the carbon from 13C data. The amounts of C derived from maize in the Ap horizon after 39 years of continuous maize cropping were 9.5% of the total organic C (where unfertilized) and 14.0% where NPK had been applied. Fertilization did not affect the residence time of carbon in the soil. The amounts of C derived from maize in water extracts were 21% of the total organic C (where unfertilized) and 22% where NPK had been applied. The extracts that were soluble in pyrophosphate and insoluble in acid were depleted in C from maize (the amounts were 5% and 7% of the total organic C, respectively). The results of the 13C natural abundance technique were used to model the dynamics of the organic C. Both the total organic C and the C derived from maize in the particle-size fraction 0–63 μm agreed well with the total and maize-derived sums of the model pools ‘inert organic matter’, ‘humified organic matter’ and ‘microbial biomass’. The model suggested that 64% (unfertilized) or 53% (NPK) of the organic C in the Ap horizon were inert. Only one of three published equations to determine the size of the inert pool agreed well with these model results.

Notes: Risk assessment of heavy metals in soil requires an estimate of the concentrations in the soil solution. In spite of the numerous studies on the distribution of Cd and Zn in soil, few measurements of the distribution coefficient in situ, Kd, have been reported. We determined the Kd of soils contaminated with Cd and Zn by measuring metal concentrations in the soil and in the soil solution and attempted to predict them from other soil variables by regression. Soil pH explained most of the variation in logKd (R2 = 0.55 for Cd and 0.70 for Zn). Introducing organic carbon content or cation exchange capacity (CEC) as second explanatory variable improved the prediction (R2 = 0.67 for Cd and 0.72 for Zn), but these regression models, however, left more than a factor of 10 of uncertainty in the predicted Kd. This large degree of uncertainty may partly be due to the variable degree of metal fixation in contaminated soils. The labile metal content was measured by isotopic dilution (E value). The E value ranged from 18 to 92% of the total metal content for Cd and from 5 to 68% for Zn. The prediction of Kd improved when metals in solution were assumed to be in equilibrium with the labile metal pool instead of the total metal pool. It seems necessary therefore to discriminate between ‘labile’ and ‘fixed’ pools to predict Kd for Cd and Zn in field contaminated soils accurately. Dilute salt extracts (e.g. 0.01 m CaCl2) can mimic soil solution and are unlikely to extract metals from the fixed pool. Concentrations of Cd and Zn in the soil solution were predicted from the concentrations of Cd and Zn in a 0.01 m CaCl2 extract. These predictions were better correlated with the observations for field contaminated soils than the predictions based on the regression equations relating logKd to soil properties (pH, CEC and organic C).

Notes: Chloropyromorphite, CPM, Pb5(PO4)3Cl, is one of the most insoluble lead minerals. Inducing the formation of CPM by application of phosphate to soil has been suggested for immobilizing Pb at contaminated sites. We have examined the effect of organic matter on the completeness and the rate of CPM precipitation and on the particle size and the mobility of CPM crystals. We did experiments at pH 3–7 and with varying content of dissolved organic C, 0–72 mg C l−1, mixing Pb(NO3)2 (0.5 mmol l−1) and phosphate (2 mmol l−1) solutions. The organic matter was extracted from samples of a forest floor. The precipitates were identified by X-ray diffraction, and their size and shape were analysed by scanning electron microscopy and by photon correlation spectroscopy. The presence of organic matter in the solutions did not affect the mass of CPM that precipitated within 30 minutes at pH 5, 6 and 7. At pH 3 and 4, however, organic matter strongly inhibited the precipitation. The particles were markedly smaller in solutions containing organic matter than without at all pHs and passed through water-saturated columns filled with calcareous sand, whereas the precipitates from the carbon-free solutions did not. We suggest that the organic matter blocked the surfaces of crystal seeds and impaired crystal growth. At high pH, organic matter may additionally decrease the crystal size of the individual crystals by increasing the number of crystal seeds. We conclude that organic matter in the solution might limit the potential of phosphate to immobilize Pb in soil because it favours the formation of mobile colloids.

Notes: Recent studies have pointed to the occurrence in soil organic matter of an insoluble macromolecular fraction, resistant to drastic alkali and acid hydrolysis. This non-hydrolysable fraction may contribute to the stable carbon pool in the soil and thus be important for the global carbon budget. We have developed a method to isolate such chemically resistant components, whilst ensuring complete elimination of the hydrolysable constituents of the organic matter but avoiding the formation of insoluble compounds via Maillard-type condensation reactions. Maize leaves, material especially susceptible to artefact formation, were used for this optimization. Several of the treatments that we tested, including the Klason lignin protocol, proved unsuitable. The most suitable protocol, by progressive hydrolysis with trifluoroacetic and hydrochloric acid, revealed a non-hydrolysable fraction in maize leaves accounting for about 5% by weight of the leaves and corresponding chiefly to lignin and condensed tannins. The protocol was applied to a forest soil and to the soil from an adjacent plot cleared 35 years ago and since cropped continuously with maize. The abundance, chemical composition and sources of the non-hydrolysable fraction of these two soils were determined by a combination of spectroscopy, pyrolysis and electron microscopy. This fraction accounted for about 6% of the total organic carbon of both soils; it contains aliphatic moieties, black carbon, melanoidins and, we think, condensed tannins.

Notes: The understanding of cation binding in the mor layer is important to correctly assess the biogeochemical cycling of metals and other cations in forested ecosystems. In a series of batch experiments, the binding of cations was examined in two mor layers from central Sweden. We examined the effect of Ca and Al on the binding of Zn, and also the binding of added Pb, Cu and Cd. Two models, WinHumicV and the Stockholm Humic Model (SHM), were tested for their ability to describe the data obtained. We found that for Zn, the pH at 50% sorption was increased from 2.8 to 4.2 after the addition of 3 mM Al. The proton titration data were well described by both WinHumicV and SHM after optimization of the concentrations of ‘active’ Al and humic substances. Applying generic parameters for cation binding produced deviations between the model simulations and the observations, particularly for the dissolved Pb and Cu concentrations, which were underestimated. A revised set of cation complexation constants was presented that improved the fit, particularly for SHM. For WinHumicV, there were still poor overall fits. The difference in model performance may be due to the greater number of adjustable parameters in the SHM, but probably also to other model-specific differences. According to the SHM simulations, the binding of Ca, Mg and Mn was mainly non-specific, whereas Pb, Cu and Al were bound as mono- or bidentate complexes. For Zn and Cd, binding occurred through both counter-ion accumulation and monodentate complexation.

Notes: Metal availability in soils is strongly related with sorption processes and the possible association of the metal ions with a particular particle-size fraction. Therefore, studies of metal retention by a soil will be aided if retention by different size fractions is also studied. Sorption of copper on a calcareous soil and its textural fractions was studied in batch assays. The soil was amended over 3 years with two agroindustrial residues, a composted olive mill sludge and vinasse. Sorption of Cu on the calcareous soil was very large (110 mmol kg−1) and was enhanced by both amendments. Metal retention by the clay fraction of the unamended soil was less than that of the whole soil, but increased dramatically after amendment with olive mill sludge. This was caused by the larger calcite content in this fraction as well as the increase in organic matter content. The amount of Cu sorbed was very large in the silt fraction, again because of the carbonate content of this fraction (300–460 g kg−1). Copper sorption decreased dramatically after removal of carbonate. Copper retention tended to be enhanced by organic amendments. This was particularly evident in the silt fraction, as a consequence of the organic matter accumulation in this fraction.Copper sorption on the calcareous soil and its silt fractions (unamended and amended) was irreversible. By contrast, desorption was measurable from all the carbonate-free samples (both whole soil and textural fractions), although in all cases a large hysteresis was observed. We conclude that carbonate was the main component responsible for the lack of reversibility.

Notes: The organic carbon content of soil is positively related to the specific surface area (SSA), but large amounts of organic matter in soil result in reduced SSA as determined by applying the Brunauer–Emmett–Teller (BET) equation to the adsorption of N2. To elucidate some of the controlling mechanisms of this relation, we determined the SSA and the enthalpy of N2 adsorption of separates with a density 〉 1.6 g cm−3 from 196 mineral horizons of forest soils before and after removal of organic matter with NaOCl. Likewise, we investigated these characteristics before and after sorption of increasing amounts of organic matter to four mineral soil samples, oxides (amorphous Al(OH)3, gibbsite, ferrihydrite, goethite, haematite), and phyllosilicates (kaolinite, illite).Sorption of organic matter reduced the SSA, depending on the amount sorbed and the type of mineral. The reduction in SSA decreased at larger organic matter loadings. The SSA of the mineral soils was positively related to the content of Fe oxyhydroxides and negatively related to the content of organic C. The strong reduction in SSA at small loadings was due primarily to the decrease in the micropores to which N2 was accessible. This suggests preferential sorption of organic matter at reactive sites in or at the mouths of micropores during the initial sorption and attachment to less reactive sites at increasing loadings. The exponential decrease of the heat of gas adsorption with the surface loading points also to a filling or clogging of micropores at early stages of organic matter accumulation. Desorption induced a small recovery of the total SSA but not of the micropore surface area.Destruction of organic matter increased the SSA of all soil samples. The SSA of the uncovered mineral matrix related strongly to the amounts of Fe oxyhydroxides and the clay. Normalized to C removed, the increase in SSA was small in topsoils and illuvial horizons of Podzols rich in C and large for the subsoils containing little C. This suggests that micropores preferentially associate with organic matter, especially at small loadings. The coverage of the surface of the soil mineral matrix as calculated from the SSA before and after destruction of organic matter was correlated only with depth, and the relation appeared to be linear.We conclude that mineralogy is the primary control of the relation between surface area and sorption of organic matter within same soil compartments (i.e. horizons). But at the scale of complete profiles, the surface accumulation and stabilization of organic matter is additionally determined by its input.

Notes: Cadmium (Cd) inputs and losses from agricultural soils are of great importance because of the potential adverse effects Cd can pose to food quality, soil health and the environment in general. One important pathway for Cd losses from soil systems is by leaching. We investigated loss of Cd from a range of contrasting New Zealand pasture soils that had received Cd predominantly from repeated applications of phosphate fertilizer. Annual leaching losses of Cd ranged between 0.27 and 0.86 g ha–l, which are less than most losses recorded elsewhere. These losses equate to between 5 and 15% of the Cd added to soil through a typical annual application of single superphosphate, which in New Zealand contains on average 280 mg Cd kg−1 P. It appears that Cd added to soil from phosphate fertilizer is fairly immobile and Cd tends to accumulate in the topsoil. The pH of the leachate and the total volume of drainage to some extent control the amount of Cd leached. Additional factors, such as the soil sorption capacity, are also important in controlling Cd movement in these pasture soils. The prediction of the amount of Cd leached using the measured concentrations of Cd in the soil solution and rainfall data resulted in an overestimation of Cd losses. Cadmium concentrations in drainage water are substantially less than the current maximum acceptable value of 3 µg l−1 for drinking water in New Zealand set by the Ministry of Health.

Notes: The potential of imaging spectroscopy for the assessment of seasonal dry-matter (DM) yield and sward quality was studied. Relationships between spatial heterogeneity of tiller density, light interception, ground cover and seasonal DM yield were developed. Sward heterogeneity was quantified by the spatial standard deviation of ground cover and of logarithmically transformed ground cover, and patterns in ground cover transects were quantified by wavelet entropy. An experiment was conducted with eight control (C) swards, eight naturally damaged (ND) swards and twelve artificially damaged (AD) swards. Swards were established in containers and spectroscopic images were recorded twice weekly.Seasonal DM yield was linearly related to a combination of means of ground cover and index of reflection intensity (r2 = 0·93). Spatial variation of tiller density was larger for AD and ND swards than for C swards. Values of the spatial standard deviation of ground cover and wavelet entropy were larger for AD and ND swards than for C swards. A single spatial standard deviation of ground cover value of 13% discriminated ND and AD swards from C swards. Seasonal means of wavelet entropy (r2 = 0·70) and the spatial standard deviation of ground cover (r2 = 0·63) at harvest were linearly related to seasonal DM yield. It is concluded that imaging spectroscopy can be used for assessing seasonal DM yield and sward heterogeneity.

Notes: On a Flemish sandy loam soil, cut and grazed swards were compared at different levels of mineral nitrogen (N) fertilization. Economically optimal N fertilization rates were 400 (or more) and 200 kg N ha−1 yr−1 on cut and grazed swards respectively. Considering the amounts of residual soil nitrate-N in autumn, these N rates also met the current Flemish legal provisions, i.e. no more than 90 kg ha−1 nitrate-N present in the 0–90 cm soil layer, measured between 1 October and 15 November. The N use efficiency was considerably higher in cut grassland systems than in grazed systems, even when the animal component of a cut and conservation system was included. The results indicate that, for cut grasslands, two N application rates should be considered: intensively managed grasslands with high amounts of N (400 kg ha−1 yr−1 or more) or extensively managed grasslands with white clover and no more than 100 kg N ha−1 yr−1.

Notes: The aim of the investigation was to determine the influence of variations in thickness and colour of agricultural plastic film on silage preservation conditions and grass silage quality. For this purpose, 30 cylindrical plastic containers (mini-silos; 0·3 m3) were filled with chopped grass and covered with five films of different thickness and colour: 90 μm, white; 125 μm, green; 150 μm, black; 200 μm, green and 200 μm, white. Four replications of each film type were placed in the open air. Two replications were housed indoors and exposed to an ‘artificial sky’ in a test apparatus. The surface temperature of the films was found to be strongly dependent on film thickness and colour. Results of the chemical analysis of silages did not reveal any significant influence of the films. This was also the case when restricting the analysis to the uppermost silage layer. The results showed that under the conditions of this experiment, well preserved forage can be produced with films of differing colour, as well as of lesser thickness.

Notes: Narrow-leaved bird's-foot-trefoil (Lotus tenuis) is a perennial forage legume adapted to waterlogged and heavy and infertile soils and can replace alfalfa (Medicago sativa) in areas with these soils in Argentina. Its seeds are hard and water-impermeable but the effects of environmental factors on seed dormancy and germination are not known. The objective was to evaluate the hypothesis that water availability during seed development and maturation affects the degree of hardseededness in L. tenuis by changing seed coat properties, conditioning water uptake through the seed coat; and subsequently affecting dormancy, germination and speed of germination. Seeds were harvested in December/January and in February in both 1993/1994 and 1994/1995 from a permanent pasture of L. tenuis growing in a Hapludol soil in San Miguel del Monte province of Buenos Aires. Environmental conditions of each anthesis-harvest period were determined. Seeds of each harvest were subjected to chilling, washing and mechanical scarification. After 12 months seeds from each harvest were observed in a scanning electron microscope. The water deficit of the soil and relative humidity were greater in the second than the first anthesis-harvest period in both seasons. In 1993/1994 the control treatment in December had a higher germination rate than the February control seeds (0·40 vs. 0·20) and a faster germination rate. Mechanical scarification and chilling significantly enhanced the germination rate (0·95) and its speed in seeds of both harvests. Low temperatures significantly enhanced germination rate, starting after 60 d for the seeds harvested in December, and 90 d for the seeds harvested in February. In 1994/1995 the results were similar but both the January and February control treatments had higher germination rates (0·60 vs. 0·40) than in the previous year. Seeds harvested in February were more dormant in both years. These differences could be explained by the conditions in February anthesis-harvest period in both years that could have hastened the natural dehydration process of seed, changing integument structure and enhancing its impermeability.

Notes: In a replicated field experiment carried out in Northern Ireland in 1998, the effects of sowing date (17 April, 5 May, 19 May and 1 June), cultivar of forage maize (Hudson and Diamant) and treatments with no mulch (NP), total cover plastic mulch (TC), TC plastic mulch removed at eight-leaf growth stage (EL) and punch plastic mulch (PU) on the rate of development of the crop and the accumulation of dry matter (DM) in the whole plant and cobs were described. Soil and air temperatures under the mulch treatments and in the open were recorded and the daily accumulation of Ontario heat units (OUs) calculated for each treatment based on the air temperatures experienced by the crop for the periods that it was under plastic mulch and in the open.The interval from sowing to emergence was proportional to the accumulated heat units above a soil base temperature of 8·2°C. The phenology of leaf emergence varied widely in terms of calendar date across the sowing date and plastic mulch treatments but relative to adjusted OUs the treatments were more closely aligned. Treatment PU advanced the crop less than the other mulch treatments relative to calendar date but, relative to OUs, more than these treatments. Physical damage to plants emerging through the TC treatment and air temperatures exceeding 40°C during the first month under treatments TC and EL did not appear to retard physiological development. The total adjusted OUs to reach 50% silking ranged from 1432 to 1753. Close relationships were found between the total OUs from silking to harvest and the whole crop DM content, cob DM content, cob yield and starch concentration of the whole crop at harvest so that differences between the treatments could largely be accounted for by the differences in silking date. It was concluded that the OU system can provide a reasonable model of maize growth for crops sown under TC plastic mulch providing air temperatures under the plastic are used for the period that the crop experiences them. However, the OU system is less reliable for crops grown under punch plastic because of the soil warming effect of the mulch that is not taken into account by the OU system.

Notes: Three Lolium perenne L. genotypes collected from different natural habitats were tested for the effects of their fungal endophyte Neotyphodium spp. on plant growth and seed yield. Half the clones of the originally infected plants were subjected to fungicide treatment to eradicate the endophytes. In an experiment, the clones were planted separately into pots and were either watered adequately or subjected to drought stress. In the genotype collected from a dry site, the endophyte infection reduced plant growth at an adequate water supply, but increased regrowth under drought. In the genotype from a periodically either flooded or dry site, endophyte infection significantly promoted the development of reproductive tillers and seed production (effects which are associated with adaptation to drought). In contrast, the genotype that originated from a wet site showed higher sensitivity to drought stress when endophyte infection was present. The results suggest that environmental conditions in the original habitat of the plants may influence the symbiotic interaction between plant and fungus, probably through natural selection. However, endophyte-induced increases in root dry weight and root/shoot ratio were recorded for all three genotypes. These features could be beneficial for plant persistence, especially on sites where water is the growth-limiting factor.

Notes: To test whether or not the ‘stay-green’ (SG) characteristic confers benefits in terms of crop yield or distribution of dry matter (DM) in selected forage maize cultivars, an experiment was conducted in 1998 and 1999 at two sites in England: Writtle College, Essex and the University of Leeds, West Yorkshire. Five SG and five conventional (C) cultivars of forage maize were grown in replicated field-scale plots at each site in both years. One-metre lengths of single rows in each plot were harvested by hand, leaving a 20-cm stubble, on four occasions each year over 3-week periods (harvest 1 to harvest 4), prior to the harvest of the remainder of the fields. Plants were chopped, mixed and a subsample taken for determination of DM content by oven-drying. Mean yields of whole plant DM were similar between SG and C cultivars. Both yield of DM and proportion of ear in the total plant DM increased from harvest 1 to harvest 4 (P 〈 0·01). The increase in DM yield between harvest 1 and harvest 4 was greater for C than for SG cultivars (P 〈 0·05). Within sites there were no differences in the concentration of whole plant DM between SG and C cultivars, which increased from harvest 1 to harvest 4 (P 〈 0·001). The proportion of ear DM in the whole plant DM tended to be higher for C than for SG cultivars in both years and increased (P 〈 0·001) from harvest 1 to harvest 4. The concentration of DM in the ear fraction was higher (P 〈 0·05) for C than for SG cultivars. We conclude that differences between SG and C cultivars of forage maize are likely to be relatively small when grown in the English climate and harvested after the same growing period.

Notes: Bite depth was measured in four experiments in which grazing cows were offered, individually, patches of perennial ryegrass swards, typically 0·9 m × 0·9 m, of contrasting structural composition within linear sequences of eighteen to twenty-seven patches. Bite depths were analysed in relation to the independent effects of pseudo-stem height, re-growth depth, stubble height and sward height. In vegetative swards comprising predominantly leaf, with re-growth and stubble strata of vegetative origin, bite depth was strongly related to sward height. However, when the leaf–stem contrast between strata increased, bite depth was strongly correlated with the depth of re-growth. Cows were observed to penetrate into a mature stubble stratum with increasing sward height, indicating that stubble height is only a partial regulator of bite depth. In an experiment designed to investigate the independent effects of pseudo-stem and sward height, pseudo-stem was only a partial regulator of bite depth. Evidence to support the concept that bite depth is a fixed proportion of sward height across swards of different structure was inconsistent, but there was evidence of a maximum bite depth of 0·70 of sward height. There were also indications that bite depth was conditioned by the number of bites removed. This suggested that cows initially took a cautious approach to grazing, building up bite depth with feedback over the first 20–30 bites in a new patch. Behaviour at the current patch was not affected by the characteristics of the preceding or succeeding patch in sequence.

Notes: A sulphur (S)-deficient top soil was used in a pot experiment to investigate the effect of S supply on shoot and root growth and development in alfalfa (Medicago sativa L.). The treatments consisted of three rates of addition of S: 0, 20 and 40 mg kg−1 soil and each was replicated four times. Alfalfa was harvested at 15, 30, 45, 60 and 75 d after seedling emergence.By the end of the experiment, plants with S supply had a significantly larger leaf area, heavier leaf, shoot and root dry weight per pot than controls. The effects of adding S also significantly increased plant height, basal stem diameter, chlorophyll concentration of young leaves, root length and root surface area compared with controls. The effects of S were greater on shoots than on roots. The ratio of root to shoot dry weight was 0·47 when S was supplied and 0·88 without added S, indicating that c. 0·32 and 0·47 of the total net photosynthate, produced with or without S supply, respectively, were used for the development of roots. Overall, overcoming S deficiency resulted in a significant increase in shoot and root growth.

Notes: Kudzu [Pueraria lobata (Willd.) Ohwi.], a vigorous, perennial warm-season legume, grows widely throughout the south-eastern United States, predominantly as a volunteer species. It is tolerant of drought and acidic, infertile soils and may have potential as a low-input forage for livestock. A field experiment was undertaken to determine the effects of cutting date and frequency on yield and nutritive value of kudzu (20-year-old stand with no fertilizer or lime inputs) in central Georgia. The cutting treatments included an uncut control, and plots cut once (September), twice (July and September), and three times (June, July, and September) during the 1994 growing season. Dry matter (DM) production and forage quality were determined for total herbage, leaf and stem tissues from quadrat samples taken on all plots in June, July, September, and November (after a killing frost) in 1994, and in June, 1995. Total herbage and leaf DM production was highest for the three-harvest system and lowest in the no-cut control plots in 1994, but these results were reversed in the harvest made in 1995. Total herbage production and crude protein concentrations were similar in kudzu cut in the initial summer harvest (either June, July, or September) during the first year. Whole plant and stem in vitro dry matter digestibility (IVDMD) in these samples declined throughout the growing season, while leaf IVDMD was unchanged until the first frost. Kudzu has the potential to be a low-input forage for livestock, particularly as supplemental drought feed, or as a protein bank for summer or autumn grazing.

Notes: Abstract Cerastium holosteoides is a short-lived plant often found in small proportions on dry and mesotropic semi-natural, species-rich grassland communities. To obtain more information about its nutritive value, two experiments on Arrhenatheretum elatioris grassland were carried out to examine the effect of harvest date on in vitro organic matter digestibility (IVOMD), neutral-detergent fibre (NDF), acid-detergent fibre (ADF), acid-detergent lignin (ADL), estimated net energy for lactation (NEL) and crude protein (CP) concentrations of C. holosteoides, and selection of this plant by dairy cows grazing on semi-natural grassland. C. holosteoides starts flowering in spring and continuously develops new flowers on new branches throughout the summer. Harvests were made in relation to particular growth stages of Dactylis glomerata present in the sward: (A) tillering; (B) stem elongation; (C) ear emergence; (D) flowering; and (E) ripening.Chemical composition and nutritive value were evaluated in 1998 and 1999. With advancing maturity, IVOMD of C. holosteoides decreased from 0·771 at growth stage A to 0·485 at growth stage E. At the same time, CP concentration decreased from 153 to 69 g kg−1 dry matter (DM) and estimated NEL concentration from 6·00 to 4·07 MJ kg−1 DM. With advancing maturity, there was a significant increase in NDF, ADF and ADL concentrations. In the summer harvest season, C. holosteoides contained significantly higher NDF, ADF and ADL concentrations, lower NEL concentration and had a lower IVOMD value than in the spring. Differences between years were also found for IVOMD and for NDF, ADF, ADL and NEL concentrations.In a grazing experiment in the year 1999, at growth stage B, Simmental cows grazed an A. elatioris sward in which the main species was D. glomerata (0·092), and the proportion of C. holosteoides was 0·034. C. holosteoides was, on average, grazed by cows to the same relative extent as other species in the sward.

Notes: Abstract Two experiments were carried out to evaluate the performance of blends of three white clover (Trifolium repens L.) varieties in comparison with the component varieties and three other varieties sown individually in a mixture with perennial ryegrass (Lolium perenne L.). The plots were grazed rotationally in Experiment 1 by cattle and sheep and in Experiment 2 by sheep alone. In both experiments, the blend was composed of three medium-leaved varieties (AberDai, AberVantage and AberHerald), but with different relative contributions of the three varieties in the two experiments. Dry matter (DM) yields of white clover and perennial ryegrass were assessed in replicate plots for two years (1999 and 2000) after the establishment year. In Experiment 1, there was no significant difference between the DM yields of white clover or perennial ryegrass in either year. The decline in DM yield of white clover between years that was observed for some varieties was not found for the blend. In Experiment 2, significant differences were found in DM yields of white clover in both years. In 1999, AberDai had the highest DM yield. In 2000, AberHerald and AberVantage had the highest DM yields, and AberDai showed a decline in DM yield that was mirrored by the mean for all the white clover varieties. In both experiments, the blend did not show significantly higher DM yield than one or more of its components; indeed, in Experiment 2, it was significantly lower yielding than AberDai in 1999. However, where one component of the blend declined in DM yield between years, this was compensated for by an increase in the yield of another component. These preliminary findings suggest that the yield stability of blends may give them a potential role in agricultural practice.

Notes: Daily net canopy photosynthesis (Pn) of cocksfoot (Dactylis glomerata L.) was predicted for combinations of temperature, herbage nitrogen (N) concentration and water status from the integration of models of leaf photosynthesis of the light-saturated photosynthetic rate (Pmax), photosynthetic efficiency (α) and the degree of curvature (θ) of leaf light-response curves. The effect on Pn, maximum Pn (Pn max) and the optimum leaf area index (LAI at Pn max) was examined when any one of these factors was limiting. The ranges that gave the optimum values of Pn (Pn max = 30·8–33·5 g CO2m−2 d−1) for temperature (19–22°C) and N concentration (40–50 g N kg−1 DM) were smaller than those for net leaf photosynthesis. Also, Pn fell to 0 at a lower level of water stress (pre-dawn leaf water potential, ψlp = −12·5 bar) than for Pmax. The canopy photosynthesis model was then used to compare predicted and measured dry matter (DM) production for cocksfoot pastures grown under a diverse range of environmental conditions with field data from New Zealand and Argentina. To predict DM production leaf area index and leaf canopy angle were included from field measurements. The model explained about 0·85 of the variation in cocksfoot DM production for the range of 6·5–134 kg DM ha−1 d−1. The canopy model overestimated the DM production by 0·10 which indicates that a further Pmax function for leaves of different ages and a partitioning sub-model may be needed to improve predictions of DM production.

Notes: The aim was to compare the effects of additives on direct cut silages of pure timothy and timothy mixed with tetraploid red clover. First and second growth cuts were ensiled during three consecutive years, 1994, 1995 and 1996, either without any additive or with the addition of formic acid, or lactic acid bacteria in combination with molasses. Effects of the additives on the degradation characteristics of the herbage and the silages were analysed using an automatic in vitro gas production (GP) technique. At the end of the in vitro procedures, organic matter and neutral-detergent fibre (NDF) degradabilities were determined.The tetraploid red clover persisted in the leys during the 3 years and was the dominant species at the second growth in the mixed leys. The herbage from the mixed crops had lower dry-matter contents, higher crude protein concentrations and higher buffering capacity compared with the pure timothy at both cuts. In general, the additives reduced pH, and the concentrations of ammonium-N and acetic acid in the silages. The treated silages had a more rapid faster GP in both crops.The silages from the mixed crop benefited more from the additives compared with the grass silages. The additives affected the soluble fractions as well as the NDF degradability of the silages of the mixed crop more than those fractions of the grass silages. The addition of molasses in combination with a commercial inocula resulted in increased production of lactic acid and ethanol in silages from both crops. The silages without additives could not meet the requirements for good silages according to the standards of the Swedish dairy industry.

Notes: Interspecific hybridization with the close relative Trifolium nigrescens Viv. (Ball clover) is a possible strategy to increase the seed yield potential of white clover (T. repens L.). Fertile F1 plants have been used as the basis for several generations of backcrossing using T. repens as the recurrent parent. Forage quality of the parental species and backcross hybrids when grown in mixtures with perennial ryegrass (Lolium perenne L.) was compared in field plots over three harvest years. The dry-matter digestibility (DMD) and crude protein (CP) concentration of the legume fraction was greater than that of perennial ryegrass, but the water-soluble carbohydrate (WSC) concentration of the legume components was lower than that of perennial ryegrass. Differences in forage quality between T. repens and the backcross hybrids were relatively small. The WSC concentration of the backcrosses was less than T. repens but the CP concentration was greater. Significant differences in the forage quality of the companion grass were observed when grown with the parental species and the hybrids; however, these differences were attributed to the plots with T. nigrescens and the F1 plants, where the clover content was low. Few differences in the forage quality of the grass were measured when grown with T. repens and the backcross hybrids. The impact of these results on the use of these hybrids in cultivar development programmes is discussed.

Notes: The aim was to study the effects of white clover cultivar and combinations with perennial ryegrass cultivars on seedling establishment in autumn-sown swards and on winter survival of seedlings. Large-leaved white clover cv. Alice and small-leaved white clover cv. Gwenda, and an erect and a prostrate perennial ryegrass cultivar were sown in autumn in pure stands and as four binary grass-clover mixtures. Mixtures of white clover cv. Huia and Aberherald with perennial ryegrass were also sown. Companion grasses had no significant impact on the establishment of white clover. The number of seedlings of white clover cv. Alice in mixtures (335 m−2) was higher than cv. Gwenda (183 m−2) and pure swards had similar white clover population densities as mixed swards. White clover cv. Huia tended to have more seedlings than Aberherald (355 and 205 m−2 respectively). No stolons were produced prior to a severe winter, because of the late sowing date. Winter survival of clover seedlings was 0·56 in mixtures and 0·69 in pure stands, irrespective of white clover or companion grass cultivar. Stolon development of white clover in autumn is often considered essential for overwintering survival and spring growth. In this study, there was considerable survival of the non-stoloniferous tap-rooted seedlings of all four clover cultivars despite a severe winter.

Notes: The recycling of sewage sludge or biosolids to grassland is strategically important in the European Union (EU) and its use is tightly regulated to control the risk of pathogen transfer to animals and the food chain. Sewage sludges not only contain valuable concentrations of beneficial nutrients, but also elevated concentrations of potentially toxic metals (PTM) compared with average background concentrations in the soil. The EC and UK regulations refer to six PTM, Cd, Pb, Cu, Zn, Ni and Hg, with provisional regulations for Cr, that have to be controlled to prevent detrimental effects on soil and animal health. Despite these regulations, there is still a danger that grazing animals may ingest elevated concentrations of PTM. Biosolids may adhere to herbage after the surface application of sewage sludge to grassland. The repeated surface application of sewage sludge to grassland can lead to elevated concentrations of PTM at the soil surface that may be ingested, together with soil and herbage, by grazing ruminants. This may lead to accumulation of Cd or Pb in liver or kidney. The risk to the human food chain is considered to be low, but the impact on the environment is still unknown. There is little information, for example, on the amount of soil and PTMs that may become incorporated into conserved grass. At present EU and UK legislation and voluntary codes of practice have been developed to protect animal from pathogens in sewage sludge and to minimize any potential risks from accumulation of PTM. The background and implementation of the legislation are examined in this review, and the source and mechanisms of accumulation of PTM by the grazing animal are evaluated.

Notes: Six mid-lactation multiparous Holstein–Friesian dairy cows were used to examine the potential of a fermented whole-crop barley (Hordeum vulgare)/kale (Brassica oleracea) bi-crop as a feed compared with a first-cut perennial ryegrass silage. The barley/kale bi-crop was grown as a strip intercrop, and was harvested and ensiled as an intimate mixture [0·80 barley and 0·20 kale on a dry-matter (DM) basis]. Animals were offered ad libitum access to one of three experimental diets in a duplicated Latin Square design experiment: (i) Bi-crop (the barley/kale bi-crop); (ii) Grass (the grass silage); and (iii) Mix (a 1:1 fresh mixture of Bi-crop and Grass). All animals also received a standard dairy concentrate at a rate of 4 kg d−1 in equal portions at each of two milkings. The Bi-crop and Grass silages contained 346 and 293 g DM kg−1, 108 and 168 g crude protein kg−1 DM, 268 and 36 g starch kg−1 DM, and had pH values of 3·87 and 3·80 respectively. Animals offered the two bi-crop silage-containing diets consumed more forage DM than those offered grass silage (14·6, 14·9 and 12·6 kg DM d−1 for Bi-crop, Mix and Grass respectively; s.e.d. 0·45, P 〈 0·01) and yielded more milk (24·0, 23·9, 22·6 kg d−1 for Bi-crop, Mix and Grass respectively; s.e.d. 0·26, P 〈 0·01). However, differences in the partitioning of dietary nitrogen towards milk protein and away from excretion in urine suggest a more efficient (rumen) utilization of feed protein by animals offered diets containing the bi-crop silage. It is concluded that, despite having a low crude protein concentration, barley/kale bi-crop silage offers excellent potential as a feed for lactating dairy cows.

Notes: Plant roots influence the biological, chemical and physical properties of rhizosphere soil. These effects are a consequence of their growth, their activity and the exudation of organic compounds from them. In natural ecosystems, the linkages between inputs of carbon from plants and microbial activity driven by these inputs are central to our understanding of nutrient cycling in soil and the productivity of these systems. This coupling of plant and microbial productivity is also of increasing importance in agriculture, where the shift towards low-input systems increases the dependence of plant production on nutrient cycling, as opposed to fertilizers. This review considers the processes by which plants can influence the cycling of nutrients in soil, and in particular the importance of organic inputs from roots in driving microbially mediated transformations of N. This coupling of plant inputs to the functioning of the microbial community is beneficial for acquisition of N by plants, particularly in low-input systems. This occurs through stimulation of microbes that produce exoenzymes that degrade organic matter, and by promoting cycling of N immobilized in the microbial biomass via predation by protozoa. Also, plants increase the cycling of N by changes in exudation in response to nitrogen supply around roots, and in response to browsing by herbivores. Plants can release compounds in exudates that directly affect the expression of genes in microbes, and this may be an important way of controlling their function to the benefit of the plant.

Notes: It seems possible that soil potential nitrification rates (PNRs) are determined by the size and structure of both the eubacterial and nitrifier populations. We have examined this possibility by comparing the structure of the eubacterial community with the subcomponents and dynamics of the ammonium-oxidizer population, within and between three arable fields. PNRs were significantly different between the three fields and also showed significantly different temporal patterns within each field. The use of eubacterial primers in polymerase chain reaction–denaturing gel gradient electrophoresis (PCR–DGGE) analyses indicated that the bacterial community structure in each field was significantly different from that in the others, and that the bacterial components of these communities changed with time through the season. In contrast, PCR–DGGE analyses specific to ammonium oxidizers suggested that the populations in all three fields were similar in types and did not vary with time. Competitive PCR suggested that there were large and biologically significant differences in the size of the nitrifier population between the three fields, but that within each individual field populations did not change over time. Sequencing identified the ammonium oxidizers in the Nitrosospira spp. cluster. There was also no relation between the size of the nitrifier populations and PNR. Functional expression, as PNR, apparently responded to changes in eubacterial community structure.

Notes: The diversity and functional type of plants can affect the microbial biomass in the soil, its respiratory activity and the diversity of its bacterial population. We have studied these effects in microcosms of reconstituted limestone grassland containing (i) a 12-species mixture of graminoids and forbs, (ii) a monoculture of the sedge Carex flacca, (iii) a monoculture of the grass Festuca ovina, and (iv) similar soil without plants. Microbial biomass was significantly greater in soil under monocultures of F. ovina than in the other microcosms. Basal respiration was largest in the F. ovina and mixed-species treatments where values were more than double those in the C. flacca and bare soil microcosms. The basal respiration was strongly linearly related to plant productivity (r = 0.89). Analysis of the active bacterial population by denaturing gradient gel electrophoresis of 16S rRNA revealed its diversity to be significantly greater in the C. flacca and bare soil treatments than in the F. ovina or mixed-species microcosms. This suggests that the functional type of plants has a strong influence on the composition of the bacterial community. We hypothesize that the discriminating functional attribute leading to a reduction of bacterial diversity in these microcosms was the presence in the F. ovina and mixed-plant communities of an active arbuscular–mycorrhizal mycelium that is absent from bare soil and monocultures of C. flacca.

Notes: The production of fine roots is one of the principal means by which carbon, fixed during photosynthesis, enters the soil, and quantifying the production for particular combinations of environmental and biotic factors is important for predicting the sequestration of carbon in the soils of grassland ecosystems. Arbuscular mycorrhizal fungi (AMF) can have a major effect on the production of roots, and we studied how colonization by AMF affects the lifespan of roots. Twenty per cent of control roots of Trifolium repens survived for longer than 42 days whereas 37% survived that long in AMF-colonized plants. The overall survival of the roots of Lolium perenne was less than in T. repens: around 10% of roots survived beyond 42 days and this was not affected by AMF colonization. Previous studies have shown that lifespans of roots can be affected by temperature. We tested the hypothesis that these observations are linked to a change in the morphology of the root system caused by temperature and also by AMF. We found that inoculation with AMF in a microcosm study using Plantago lanceolata grown at various temperatures, with and without AMF, showed no clear effect of AMF on branching patterns. Temperature had a significant effect on total lengths, numbers and branching rates of some higher orders of roots. Total lengths of both secondary and tertiary roots grown at 27°C were about double those of plants grown at 15°C. Colonization by AMF tended to reduce this effect. Evidently the effect of colonization by AMF on root lifespan depends on the species. Increased branching, and thus a greater proportion of ephemeral roots, was responsible for shortening the lives of the roots at increased temperature, which suggests a strong link between lifespan and morphology.

Notes: The behaviour and fate of trace metals, in particular lead and cadmium, when they contaminate the soil as atmospheric fall-out are not well understood. To improve our understanding, we incorporated pure compounds of lead and cadmium into samples taken from surface horizons of three chemically contrasting soils and monitored the changes in their speciation by analysing the soil solution. In most instances the concentrations of trace metals in solution were maximal during the first few days after mixing the contaminants with the soil, and depended strongly on soil type. The exception was when the contaminant was added as sulphide particles. The initial speciation of metals also influenced their solubility, following a decreasing order which did not depend on the soil type:〈displayedItem type="mathematics" xml:id="m1" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:13510754:EJSS527:EJSS_527_m1"/〉〈displayedItem type="mathematics" xml:id="m2" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:13510754:EJSS527:EJSS_527_m2"/〉Lead sulphide was progressively oxidized, but cadmium sulphide was hardly dissolved. When lead was added as sulphate, between 10 and 20% of lead particles dissolved, regardless of the soil type. For the other species, dissolution was enhanced at lower soil pH. Thermodynamic calculations with the WinHumic V program indicated that the solution was not saturated with respect to lead sulphate. We conclude that dissolution must be limited by the adsorption of inhibitors on reactive surfaces. The calculations also showed that precipitation of chloropyromorphite probably controls lead concentration in leachate from the acid organic soil. Finally, both soil type and initial speciation of contaminants control the behaviour of trace metals in soils for a time greater than a cropping season and must be considered for understanding their environmental impact.

Notes: Sewage sludge is increasingly used as an organic amendment to soil, especially to soil containing little organic matter. However, little is known about the utility of this organic amendment in the reclamation of soil polluted with heavy metals. We studied the effects of adding sewage sludge on enzymatic activities of a semi-arid soil contaminated with Cd or Ni in the laboratory. The activities of urease, phosphatase, β-glucosidase and protease-BAA were measured in soil containing concentrations of Cd or Ni in the range 0–8000 mg kg−1 soil, and their inhibition was compared with those of the enzymatic activities in the same soil amended with sewage sludge and containing similar concentrations of the heavy metals. The inhibition was tested for three different incubation times to determine changes in the effect of the heavy metals on hydrolase activity with the time elapsed after contamination. Ecological dose (ED) values of Cd and Ni were calculated from three mathematical models which described the inhibition of the enzymatic activities with increasing concentrations of heavy metal in the soil. For urease and phosphatase activities, the ED values for Cd and Ni increased after application of sewage sludge to soil, indicating a decrease in Cd and Ni toxicity. The other two enzymes (β-glucosidase and protease-BAA) were less sensitive to Cd or Ni contamination, and it was more difficult to determine whether addition of sewage sludge had affected the inhibition of these enzymes by the heavy metals.

Notes: Current wet chemical methods for the speciation of sulphur (S) in soils are inaccurate and do not allow one to assess the S speciation of individual soil particles and colloids. X-ray microscopy and Near Edge X-ray Absorption Fine structure Spectroscopy (NEXAFS) can be used to study individual species of S at the K-adsorption edge. We have used these techniques to identify and quantify S species in bulk soil, soil particles and colloids from Oh and Bh horizons of two forested Podzols. The partitioning of soil sulphur as determined on bulk samples of the Oh horizons by X-ray spectromicroscopy agreed fairly well with the results of a conventional S speciation for the soil at Schluchsee, and reasonably well for that at Rotherdbach. The NEXAFS analyses on individual soil particles revealed that they are richer in reduced organic sulphur than the bulk soil for the Schluchsee Oh and richer in sulphate for Rotherdbach Oh. The techniques can be used reliably to separate and quantify sulphur species with different oxidation states in the soil. The combination of X-ray transmission and sulphur fluorescence images with unfocused and focused NEXAFS spectra at the K-adsorption edge of sulphur at specific microsites allowed us to compare the distribution of S species in bulk soil with that of distinct soil particles and soil colloids. Moreover, we can use it to assess the spatial distribution of different S species on soil particles on a scale of a few hundred nanometres.

Notes: Tillage redistributes soil and contributes significantly to the within-field soil variation, especially on topographically complex terrain. Although the basic principles of the redistribution are well understood, models for simulating the redistribution are poor predictors. This paper presents a modelling structure that allows a simulation of the redistribution of soil constituents on complex topographies for various tillage implements. The model simulates the redistribution of soil constituents by convoluting the probability distribution of the tillage displacement with the spatial distribution of the soil constituents. The probability distributions in two dimensions are derived from a series of tillage experiments conducted with a mouldboard plough at various positions in the landscape. Furthermore, the effects of topography and tillage direction on the probability distributions were characterized and implemented in the model. A first application showed that the direction of tillage significantly affects the long-term redistribution of soil constituents. The inclusion of other implements in the model was explored, and we found that data in the literature could be used for simulating the long-term effects of tillage.

Notes: The dynamics and function of humus forms in tropical forests are still poorly understood. Humus profiles in two secondary semi-evergreen woodlands in Guadeloupe (French West Indies) were analysed micromorphologically. The humus forms are described under the canopy of five dominant tree species at two sites: under Pisonia subcordata and Bursera simaruba in a secondary forest on a Leptosol (Rendzina), and under Swietenia macrophylla, Tabebuia heterophylla and B. simaruba in a plantation on a calcareous Vertisol.In the secondary forest, two distinct humus forms were observed. A calcareous Amphimull, characterized by an OH horizon comprising the faecal pellets of millipedes, is formed under the canopy of P. subcordata, which produces a litter that is rich in nitrogen. A Dysmull with a thick root mat (OFRh horizon) develops under the canopy of B. simaruba, which produces a litter rich in lignin and phenol that is consumed slowly by the soil fauna. In the plantation on the Vertisol, the activity of the endoanecic earthworm Polypheretima elongata has led to the rapid disappearance of litter and the mixing of organic and mineral material. The humus form is a Eumull and is similar under all three tree species present.

Notes: Understanding mechanisms of microaggregate formation in soils requires knowledge of their exact size distribution. With this in mind, we have used X-ray attenuation to determine the size distributions of microaggregates and primary particles in the range 0.2–63 μm, with a resolution of 100 size increments. Ten arable and grassland soils with organic C contents ranging from 14.7 to 37.7 g kg−1 were analysed. They were subjected to ultrasound at 52 J ml−1 which destroyed most aggregates 〉 63 μm to give microaggregates in the size range 1–63 μm. The size distribution of microaggregates differed significantly from that of primary particles and was largely independent of their organic C content. Microaggregates were most abundant in 19 of the 100 size increments, contributing to 92% of the major peaks of the size distribution. These preferred increments differed from those of primary particles, but the order for the two was similar. Further analysis of the size distribution revealed a larger mean weight diameter of microaggregates, depending on the size distribution of primary particles. The results suggest a major effect of the size distribution of primary particles on microaggregation, whereas land use seems to have a negligible effect. The proportion of mechanically dispersible clay decreased with increasing C content and indicates structural stability at the microscale.

Notes: What processes control the accumulation and storage of carbon (C) in the mineral subsoil beneath peat? To find out we investigated four podzolic mineral subsoil profiles from forest and beneath peat in Lakkasuo mire in central boreal Finland. The amount of C in the mineral subsoil ranged from 3.9 to 8.1 kg m−2 over a thickness of 70 cm and that in the organic horizons ranged from 1.8 to 144 kg m−2. Rates of increase of subsoil C were initially large (14 g m−2 year−1) as the upland forest soil was paludified, but decreased to 〈 2 g m−2 year−1 from 150 to 3000 years. The subsoils retained extractable aluminium (Al) but lost iron (Fe) as the surrounding forest podzols were paludified beneath the peat. A stepwise, ordinary least-squares regression indicated a strong relation (R2 = 0.91) between organic C concentration of 26 podzolic subsoil samples and dithionite–citrate–bicarbonate-extractable Fe (negative), ammonium oxalate-extractable Al (positive) and null-point concentration of dissolved organic C (DOCnp) (positive). We examined the ability of the subsoil samples to sorb dissolved organic C from a solution derived from peat. Null-point concentration of dissolved C (DOCnp) ranged from 35 to 83 mg l−1, and generally decreased from the upper to the lower parts of the profiles (average E, B and C horizon DOCnp concentrations of 64, 47 and 42 mg l−1). The DOCnp was positively correlated with percentage of soil C and silt and clay content. The concentration of dissolved organic C in pore water in the peat ranged from 12 to 60 mg l−1 (average 33 mg l−1), suggesting that the sorptive capacity of the subsoil horizons for C had been exhausted. We suggest that the increase of C contents in the subsoil beneath mires is related to adsorption of dissolved organic C and slow mineralization under anaerobic conditions.

Notes: The acidic soils of temperate forests and some pastures on former forest land characteristically contain large amounts of aluminium and hydrogen ions and small amounts of calcium and magnesium ions. The relative importance of these potential toxicity factors are assessed from published data from soils collected in the United States and Europe. Activities of ions in the soil solutions and at the surfaces of root-cell plasma membranes were computed with electrostatic models. Activities of Al3+ in soil solutions ({Al3+}) peaked at pH 4.1, and Al3+ activities at the surface of the plasma membrane ({Al3+}0) achieved a broad maximum between pH 4.1 and 4.8; thus, Al3+ intoxication is likely to be more severe in soils at pH 4.1 than in more acidic ones. Intoxication (assessed by root elongation) correlated somewhat ambiguously with ion activities, but Al3+- and H+-induced depletion of Ca2+ and Mg2+, or both, from the cell surface appears to play a role in toxicity. By contrast, experiments in solution culture, where intercorrelation among {Al3+}, {H+}, and {Ca2+} could be avoided, clearly demonstrated the following extrinsic and intrinsic effects. 1 The ions Al3+ and H+ are intrinsic toxicants. 2 They are also extrinsic toxicants because of the electrostatic displacement of Ca2+ from the surface of the plasma membrane. 3 They are extrinsic ameliorants because each electrostatically displaces the other from the surface of the plasma membrane. 4 The ion Ca2+ is an extrinsic ameliorant because of the electrostatic displacement of Al3+ and H+ from the surface of the plasma membrane. 5 It is an intrinsic ameliorant of intrinsic H+ toxicity, but not intrinsic Al3+ toxicity. 6 It meets an intrinsic requirement. 7 The ion Mg2+ resembles Ca2+ in item 4 but not items 5 and 6 in short-term cultures.In acidic soils, Al3+ may prevent H+ from becoming an intrinsic toxicant (item 3) and may induce an insufficiency of Ca2+ and Mg2+ (item 2). These findings have implications for the mechanisms by which woodland plants tolerate very acidic soils.

Notes: To investigate the mechanisms by which rice plants growing in alternately flooded and drained soils absorb soil phosphate, we grew rice in moist, flooded and flooded then moist soils, and compared the measured uptake of phosphorus (P) with that calculated using a mathematical model of uptake allowing for solubilization by various means. The theory and equations for the model are given, together with a method for solving diffusion equations near roots in a root system of increasing density. The diffusion coefficients and buffer powers of P in the soil under the different water regimes are measured by following diffusion of P to a resin sink, and the parameters describing solubilization are estimated from previously published results. In all the water regimes studied, the plants relied upon solubilization for most of their P. The roots were not mycorrhizal, as they will often not be in intermittently flooded soils. In the flooded soil, uptake was three times that in the moist soil, and was consistent with solubilization by acidification caused by roots as a result of oxidation of iron and imbalance between the intake of cations and anions. In the moist soil, the uptake was consistent with solubilization by excretion of organic anions from the roots. In the flooded then moist soil, uptake declined sharply as the soil dried because P became immobilized in the soil. However, the final uptake was similar to that in the continuously moist soil, indicating that some of the immobilized P was re-solubilized by roots, possibly by excretion of organic anions.

Notes: Rapid T1ρH relaxation and inefficient cross-polarization have long been known to affect quantitation in solid-state 13C cross-polarization (CP) NMR spectra of soil organic matter. We have developed two new techniques to overcome these problems. The first, spin accounting, enables accurate gauging of how quantitative a spectrum is likely to be. The result is expressed as the percentage of potential NMR signal that can be accounted for (Cobs). Spin accounting improves on the established spin counting technique by correcting for rapid T1ρH relaxation and inefficient cross-polarization. Spin accounting identifies three components: one that is well represented in CP spectra, one that is under-represented in CP spectra due to rapid T1ρH relaxation, and one that is under-represented in CP spectra due to inefficient cross-polarization. For a range of eight de-ashed soils, Cobs was in the range 83–106%, indicating that virtually all potential signal could be accounted for after correcting for rapid T1ρH relaxation and inefficient cross-polarization. The second new technique, RESTORE (REstoration of Spectra via TCH and T One Rho (T1ρH) Editing), generates subspectra for the three components identified in spin accounting. The sum of the three RESTORE subspectra is essentially a corrected CP spectrum. The RESTORE spectra of all eight soils more closely resembled the corresponding, and presumably quantitative, Bloch decay spectra than did the CP spectra. RESTORE identifies the types of structures underestimated by CP, and the cause of their underestimation. Rapid T1ρH relaxation most affected carbonyl and carbohydrate carbons, whereas inefficient cross-polarization most affected aromatic carbons.

Notes: Simulation models of net mineralization of nitrogen (N) in soil need to be able to incorporate the effect of soil water. Our objective was to identify and define the best way of expressing soil water and its effect on net mineralization across a range of soil types. We collated data from 12 laboratory incubation studies, including a total of 33 different soils, where rates of net mineralization of N were determined from the net accumulation of mineral N under a range of water contents at near-optimal temperatures. Measurements of water potential and limits of water content observed in the field were available for most of these soils. The percentage of pore space filled with water was estimated from measurements of soil bulk density. We found that relative water content, particularly when expressed relative to an upper and lower limit of water content observed in the field, was the best descriptor for net mineralization. The next best descriptions were soil water potential, water content relative to the optimal water content for mineralization, and percentage of pore space filled with water, with water content alone being poor. Although various functions may be used to describe the relation between relative water content and net mineralization of N, an equation for a sigmoidal curve provided the best fit, and explained 78% of the variation.

Notes: After the Chernobyl accident in 1986 the fate of radiocaesium from the fallout became of pressing concern. Specific soil amendments, as K fertilizer and specific clay minerals, promised to mitigate the worst effects. We therefore investigated the influence of bentonite and the K status of the soil on the radiocaesium equilibria in soil and on its availability to ryegrass.A sample of a sandy soil was contaminated with 134Cs and amended with K and Ca salts (0–0.97 mmol kg−1) and K bentonite (0–2%). After 4 weeks' incubation of the soil mixtures, ryegrass was grown for 18 weeks in a pot trial and harvested on seven occasions. No significant treatment effects on 134Cs activity concentrations were found at the first and second harvest. From the third harvest onwards, however, 134Cs activity concentrations in the grass were reduced up to twofold (P 〈 0.05) by increasing rates of K bentonite. Adsorption studies with 137Cs revealed that the radiocaesium interception potential (RIP) of the soil–bentonite mixtures (〉 1% bentonite) increased about 10-fold during plant growth. The RIP of the K bentonite after plant growth was up to 10 times larger than that of pure illite. The formation of specific Cs sorption sites is ascribed to the in situ illitization of the K bentonite. The increase in RIP during plant growth is reflected in a decrease in exchangeable K+ at 2% K bentonite of about 18%. Radiocaesium concentrations in grass could be reliably predicted from the Cs+ and K+ concentrations in the soil solution. Adding K bentonite to a soil contaminated with radiocaesium is effective in fixing Cs in the soil.

Notes: The dynamics of biological denitrification in riparian soil is still poorly understood. We studied the spring-time pattern of denitrifying enzyme activity (DEA) and the rate of denitrification (DNT) in two hydromorphic riparian soils, one a mollic Gleysol and the other a terric Histosol. The average DEA ranged from 73 to 1232 ng N g−1 hour−1, and DNT ranged from 4 to 36 ng N g−1 hour−1. Both DEA and DNT diminished with increasing depth in both soil types. This decrease corresponded to a decrease in total and K2SO4-extractable organic carbon and K2SO4-extractable mineral nitrogen. The DEA and DNT differed in their dynamics. The former had no evident pattern in subsurface horizons but increased with temperature at the end of spring in surface and structural horizons. The DNT diminished as the soil dried in the mollic Gleysol when the water table fell. In the terric Histosol, the water table was still too high at the end of spring to affect the DNT. The results suggest that the vertical pattern of denitrification is related to that of organic carbon content. This organic carbon content determines biological activity and the supply of carbon and nitrous oxides. In biologically active horizons temperature drives the dynamics of DEA, whereas soil moisture drives the dynamics of DNT. Our results show the importance of the dynamic soil–water relationship in controlling denitrification within the riparian zone.

Notes: To gain insight into the effect of clay mineralogy on the turnover of organic matter, we analysed the 14C activity of soil organic matter associated with clay in soils dominated by kaolinite and smectite in natural savanna systems in seven countries. Assuming that carbon inputs and outputs are in equilibrium in such soils, we took the 14C age as mean residence time of the organic matter. We corrected the 14C activity for the Suess effect, Bomb effect and difference between date of sampling and date of 14C measurement. Organic matter associated with kaolinite turned over fast (360 years on average). Organic matter associated with smectite turned over relatively slowly, with an average mean residence time for the whole clay-size fraction of 1100 years. Multiple linear regression indicates that clay mineralogy is the main factor explaining differences in the mean residence time of the organic matter extracted.

Notes: The objectives were to compare the effects of two plastic film systems [perforated (PP) and complete-cover (CC) systems] on the yield and quality of forage maize, and to study the effects of seeding rate on maize grown with, and without, plastic film. Between 1995 and 1998 (Experiments 1 and 2), comparisons were made of maize without plastic film systems (NP), sown through clear plastic film (PP) and covered with clear plastic film (CC). In the CC system, the plastic was removed manually from the crop. Two dates of removal (CC1 and CC2) were compared in 1995, while four removal dates (CC1, CC2, CC3 and CC4) were examined in 1996–98. In 1996–98, three sowing dates (early, mid-April; mid, early-May; late, mid-May) were also examined. Four seeding rates (78 200, 93 900, 107 000 and 126 000 seeds ha−1) were examined in two experiments (Experiment 3 in 1996 and Experiment 4 in 1996–98). No plastic was used in Experiment 3, while three plastic treatments (NP, PP and CC) were examined in Experiment 4. In the CC treatment, the plastic film was removed at the six- to eight-leaf stage.In Experiment 1, the PP treatment gave lower DM yields than the NP treatment due to frost damage which killed 0·30 of the plants in the PP treatment. Plants were undamaged by frost in both CC treatments, and the CC2 treatment (plastic removal at the six-leaf stage) gave significant increases in DM and grain yields. In Experiment 2, averaged over years and sowing dates, DM yields were significantly increased by all plastic film treatments except CC4. All plastic film treatments gave significantly earlier tassel emergence than the NP treatment, and significantly increased grain yields and contents of DM and grain. The highest yields of DM and grain were obtained from the PP system. Within the CC treatments, leaving the plastic film intact until the ten-leaf stage (CC4) gave lower yields of DM and grain than removing the plastic film at an earlier stage. Averaged over years, the largest DM yields were obtained from the CC system with early-sown material, while the yield differences between treatments with late-sown crops under this system were not significant. Highest DM and grain yields were obtained with early sowing, while late sowing gave lower contents of DM and grain, and later tassel emergence.In Experiments 3 and 4, DM and grain yields increased as seeding rate increased up to 126 000 seeds ha−1 with NP and CC plastic treatments. With the PP treatment, DM yield reached a plateau at 107 000 seeds ha−1. Seeding rate did not significantly affect DM content in either experiments but grain content declined in both experiments as seeding rate increased.

Notes: Two experiments investigated (1) the effect of stage of maturity at harvest in the first year on yield and persistency of red clover and lucerne when grown as monocultures and bi-crops, and (2) the effect of ensiling differing ratios of red clover and lucerne on forage quality and degree of proteolysis. Red clover (cv. Milvus) and lucerne (cv. Vertus) were established in triplicate plots at five sowing ratios:1·00 red clover, 0·75 red clover:0·25 lucerne, 0·50 red clover:0·50 lucerne, 0·25 red clover:0·75 lucerne and 1·00 lucerne. In year 1, plots were harvested in three strips, at different stages of plant maturity, either 11 (early), 13 (mid) or 15 (late) weeks after sowing. In years 2 and 3, the whole plot was harvested at each of four harvests taken during the growing season. The DM yield of lucerne in years 2 and 3 was higher than that of red clover, leading to increased yields from bi-crops with increasing proportions of lucerne. Strips harvested at the mid-stage of maturity in the first year on the 0·25 red clover:0·75 lucerne plots produced the highest DM yields overall. Ensiling red clover and lucerne bi-crops was found to combine the improved wilting properties of lucerne and the reduced proteolysis of ensiled red clover.

Notes: The effects of sward surface height (SSH) and daily herbage allowance (HA) on the defoliation pattern and grazing mechanics of early lactation dairy cows grazing on irrigated perennial ryegrass–white clover pasture were studied. The hypothesis tested was that SSH and HA affect intake and diet selection through their effects on the pattern of defoliation which is influenced by the resistance to prehension bites.Factorial combinations of two initial SSH (14 and 28 cm) and two daily HA (35 and 70 kg DM cow−1 d−1) were examined in a replicated experiment. The peak longitudinal tensile force required to break the sward portion encompassed in a 100 cm2 area [bite fracture force (BFF100)] was measured as an index of the resistance to prehension.The volume of herbage defoliated and herbage intake increased with SSH (P 〈 0·05) and HA (P 〈 0·01). Corresponding to an increase in HA from 35 to 70 kg DM cow−1 d−1, there was a proportional increase in the total defoliation area (TDA) and intake by 0·24 and 0·55 in the short sward compared with 0·16 and 0·32 in the tall sward respectively. The results of this experiment suggest that a consistent spatial pattern of reduction of the canopy exists during defoliation by cows and that the volume of sward canopy defoliated is the major variable affecting herbage intake.The BFF increased down the sward profile at a rate that was higher (P 〈 0·05) for the taller sward than for the shorter sward. It is proposed that a relatively lower resistance to prehension in the short sward compared with the tall sward explains the greater proportionate increase in TDA and intake corresponding to an increase in HA. The rate at which BFF100 increases down the sward profile is suggested as a sward physical variable that can influence the defoliation process. The estimated time and energy costs of prehension bites are discussed in the context that larger bites are handled more efficiently than smaller bites.

Notes: The potential of an imaging spectroscopy system with high spatial (0·16–1·45 mm2) and spectral resolution (5–13 nm) was explored for monitoring light interception and biomass of grass swards. Thirty-six Lolium perenne L. mini-swards were studied for a total of eleven consecutive growth periods. Hyperspectral images and light interception (LI) were recorded twice weekly. On two dates ground cover was scored visually (GCv). At harvest, leaf area index (LAI), fresh-matter yield and dry-matter yield (DMY) were determined. Classification of images yielded several estimates of the image ground cover (GCi) and the index of reflection intensity (IRI). The GCi was highly correlated with GCv (〈inlineGraphic alt="inline image" href="urn:x-wiley:01425242:GFS379:GFS_379_mu1" location="equation/GFS_379_mu1.gif"/〉 = 0·94), LAI (〈inlineGraphic alt="inline image" href="urn:x-wiley:01425242:GFS379:GFS_379_mu2" location="equation/GFS_379_mu2.gif"/〉 = 0·88) and LI (〈inlineGraphic alt="inline image" href="urn:x-wiley:01425242:GFS379:GFS_379_mu3" location="equation/GFS_379_mu3.gif"/〉 = 0·95, for dense swards under cloudy skies). However, the relationship between GCi and LI depended on sky conditions and sward structure. Under cloudy skies, LI was linearly related to GCi, whereas under clear skies, this relation was logistic. Regression analysis of GCi and yields showed correlations with 〈inlineGraphic alt="inline image" href="urn:x-wiley:01425242:GFS379:GFS_379_mu4" location="equation/GFS_379_mu4.gif"/〉 of between 0·75 and 0·82. The mean error of DMY estimates was 340 kg. In conclusion, estimates of GCi and IRI can be used to predict DMY, even for high yield levels (up to 3500 kg DM ha−1), allowing accurate, non-destructive monitoring of biomass and light interception of grass swards.

Notes: Abstract A survey of pesticide records of golf courses was conducted to ascertain the incidence of microdochium patch disease, the most important turf grass pathogen in the UK. Disease incidence has remained steady over the last 10 years, but a wide variation was found in the incidence between courses. On average, golf courses suffered more than seven separate attacks of the disease per annum, with two distinct patterns being found. In one, disease was confined to spring and autumn, while in the other, outbreaks occurred with a similar frequency throughout the year. A negative correlation was found to exist between arbuscular mycorrhizal (AM) fungal abundance and disease incidence, while addition of AM fungi to a putting green produced some evidence that this resulted in a reduction in pathogen attack. It is concluded that AM fungi may have potential for use in a biocontrol programme against microdochium patch in fine turf.

Notes: Abstract The implications for the agricultural productivity of the UK upland sheep systems of reducing nitrogen fertilizer application and lowering stocking rates on perennial ryegrass/white clover swards were studied over 4 years at a site in Wales. The system involved grazing ewes and lambs from birth to weaning on swards maintained at a constant height with surplus herbage made into silage, thereafter ewes and weaned lambs grazed on separate areas until the onset of winter with adjustments to the size of the areas grazed and utilizing surplus pasture areas for silage. Four stocking rates [SR 18, 15, 12 and 9 ewes ha−1 on the total area (grazed and ensiled)] and two levels of annual nitrogen fertilizer application (N 200 and 50 kg ha−1) were studied in five treatments (N200/SR18, N200/SR15, N50/SR15, N50/SR12 and N50/SR9). Average white clover content was negatively correlated with the level of annual nitrogen fertilizer application. White clover content of the swards was maintained over the duration of the experiment with an increasing proportion of clover in the swards receiving 50 kg N ha−1. Control of sward height and the contribution from white clover resulted in similar levels of lamb liveweight gain from birth to weaning in all treatments but fewer lambs reached the slaughter live weight by September at the higher stocking rates and with the lower level of fertilizer application. Three of the five treatments provided adequate winter fodder as silage (N200/SR15, N50/SR12 and N50/SR9). Because of the failure to make adequate winter fodder and the failure of white clover to fully compensate for reduction in nitrogen fertilizer application, it is concluded that nitrogen fertilizer can only be reduced on upland sheep pastures if accompanied by reduced stocking rates.

Notes: Silages were made from pure crops of perennial ryegrass, red clover and white clover over 2 years. In all but one case the silage was stored as bales. A silage additive specially adapted for bales (Kofasil UltraTM) was used for all silages and they were all of good hygienic quality. The additive contained sodium nitrite, hexamethylene, tetraamine sodium bensoate and sodium propionate. The silages were offered ad libitum, either pure or mixed [grass/clover 0·50/0·50 on a dry-matter (DM) basis] with a fixed amount (8 kg) of concentrate. Two experiments, one in each year, were performed with high-yielding multiparous dairy cows in mid-lactation, and both rumen-cannulated and intact cows were used. The experiments were carried out using an incomplete changeover design with fifteen cows and five treatments each year.The cows consumed large quantities of these silages (12·7–16·3 kg DM per cow per day). The highest intakes were obtained when the red clover and the 0·50 red clover:0·50 perennial ryegrass silage diets were offered. However, there was a difference between years. In year 1, 0·50 red clover:0·50 perennial ryegrass and 0·50 white clover:0·50 perennial ryegrass silage diets showed the highest intakes while pure perennial ryegrass and white clover silage diets gave lower intakes. In year 2 the highest intake of silage was obtained when the diet containing silage from red clover from a second cut was offered, while the silage from red clover from a first cut gave the lowest intake. The voluntary intakes of silages from white clover and perennial ryegrass were intermediate. No cases of bloat or other digestive disturbances were observed. Milk yield was significantly lower for the perennial ryegrass silage diet compared with all other diets in year 1. In year 2 milk yield was highest for the white clover silage diets and lowest for the red clover silage diets from both cuts. In year 1 there were relatively small differences in milk composition while in year 2 milk fat content was significantly lower with white clover silage diet and milk protein content was significantly higher with the perennial ryegrass diet. The overall conclusion from these experiments was that cows were able to consume large quantities of pure legume silage without serious disturbance to their metabolism. Differences in measurements of rumen metabolism were found between diets and especially between years. Milk production differences appears to be coupled to both differences in rumen physical characteristics, such as passage rate and particle size as well as differences in volatile fatty acid production in the rumen.

Notes: Plants that form ericoid mycorrhizal associations are widespread in harsh habitats. Ericoid mycorrhizal fungal endophytes are a genetically diverse group, and they appear to be able to alleviate certain environmental stresses and so facilitate the establishment and survival of Ericaceae. Some of the fungal taxa that form ericoid mycorrhizas, or at least closely related strains, also form associations with other plant hosts (trees and leafy liverworts). The functional significance of these associations and putative mycelial links between Ericaceae and other plant taxa, however, remain unclear. Evidence from environments that are contaminated by toxic metals indicates that ericoid mycorrhizal fungal endophytes, and in some instances their plant hosts, can evolve resistance to these metals. The apparent ability of these endophytes to develop resistance enables ericoid mycorrhizal plants to colonize polluted soil. This seems to be a major factor in the success of ericoid mycorrhizal taxa in a range of harsh environments.

Notes: Genetically modified plants and their residues may have direct effects on ecosystem processes. We aimed to determine the amount in soil of the insecticidal δ-endotoxin, originally from the bacterium Bacillus thuringiensis, introduced into soil by root exudates and residues from genetically modified maize, to compare the short-term rates of decay of Bt-maize and non-Bt-maize, and to determine the rate at which the toxin in Bt-maize leaves decomposes in soil. Intact soil, size fractions of soil, soluble fractions from soil and fractions of organic residues from a field where Bt-maize had been cultivated for 4 years were analysed for the Btδ-endotoxin. Traces of the δ-endotoxin were detected in the whole (unfractionated) soil, the water-soluble fractions, and some of the particle-size fractions, but it was sufficiently concentrated only in the 〉 2000-µm size fraction to be quantified. The δ-endotoxin concentrations in this fraction ranged between 0.4 and 4.4 ng toxin g−1 fraction, which equated to 70, 6 and 50 mg toxin m−2 in the 0–15, 15–30 and 30–60 cm depths, respectively (or 126 mg toxin m−2 over the 0–60 cm depth) in the field in June (early summer). The 〉 2000-µm size fraction was a mixture of light- and dark-coloured organic material and mineral material comprising sand grains and stable aggregates. For samples collected early in the growing season, most of the detected δ-endotoxin was present in the light-coloured organic material, which was comprised of primarily live roots. However, recognizable maize residues, probably from previous years' crops, also contained δ-endotoxin. In a laboratory incubation study, Bt- and non-Bt-maize residues were added to soil and incubated for 43 days. There was no detectable difference in the decomposition of plant material from the two lines of maize, as determined by CO2 production. The quantity of δ-endotoxin in the decomposing plant material and soil mixtures declined rapidly with time during the incubation, with none being detectable after 14 days. The rapid disappearance of the δ-endotoxin occurred at a rate similar to that of the water-soluble components of the maize residues. The results suggested that much of the δ-endotoxin in crop residues is highly labile and quickly decomposes in soil, but that a small fraction may be protected from decay in relatively recalcitrant residues.

Notes: This review examines the interactions between soil physical factors and the biological processes responsible for the production and consumption in soils of greenhouse gases. The release of CO2 by aerobic respiration is a non-linear function of temperature over a wide range of soil water contents, but becomes a function of water content as a soil dries out. Some of the reported variation in the temperature response may be attributable simply to measurement procedures. Lowering the water table in organic soils by drainage increases the release of soil carbon as CO2 in some but not all environments, and reduces the quantity of CH4 emitted to the atmosphere. Ebullition and diffusion through the aerenchyma of rice and plants in natural wetlands both contribute substantially to the emission of CH4; the proportion of the emissions taking place by each pathway varies seasonally. Aerated soils are a sink for atmospheric CH4, through microbial oxidation. The main control on oxidation rate is gas diffusivity, and the temperature response is small. Nitrous oxide is the third greenhouse gas produced in soils, together with NO, a precursor of tropospheric ozone (a short-lived greenhouse gas). Emission of N2O increases markedly with increasing temperature, and this is attributed to increases in the anaerobic volume fraction, brought about by an increased respiratory sink for O2. Increases in water-filled pore space also result in increased anaerobic volume; again, the outcome is an exponential increase in N2O emission. The review draws substantially on sources from beyond the normal range of soil science literature, and is intended to promote integration of ideas, not only between soil biology and soil physics, but also over a wider range of interacting disciplines.

Notes: We compared functional diversity in 6- to 150-year-old sites on two primary successional glacier forelands (Ödenwinkelkees and Rotmoosferner, Austria) and related these changes to properties of their habitat in the soil (pH, soil organic matter, mineral nitrogen, phosphorus). Comparisons were made with land undisturbed for 9500 years immediately outside the glacier foreland. The functional diversity of the soil microflora was assessed based on microbial processes (N mineralization, ammonium oxidation, arginine deaminase) as well as on the activities of soil enzymes (protease, urease, xylanase, phosphatase, arylsulphatase). On both chronosequences, functional diversity (Shannon diversity index and evenness) and enzyme activity increased up to an age of 50 years, while older soils appeared to have reached a temporary steady state. The values of microbial biomass and enzyme activity were generally smaller in the Ödenwinkel soils than in the Rotmoos sequence, indicating that primary input of carbon from plant growth was less. Functional diversity increased with increasing plant development and organic matter accumulation, explaining similarities in enzyme activity patterns in the sequences. The local climates might also have contributed to the magnitude of the changes. Our data suggest that microbial functional diversity reached stability within 50 years' succession.

Notes: The relation between the biodegradation and mineralization of soil organic matter and the bacterial solubilization and mobilization of iron in soils of the humid tropics is not clear. We therefore studied how microbial activity mobilized iron in a typical swamp soil of the humid tropics using two complementary approaches. By analysing soil water we found that the swamps (20% of the catchment) are the major sites of mineral weathering. Bacteria caused the solubilization of ferrous iron, produced ammonium, released organic soluble compounds, and caused the disappearance of nitrate. The waterlogged soil of the swamp (Gleysol) degraded and mineralized organic matter, producing CO2 and NH4+, and the amount of that activity depended on the amount, availability and quality of the organic matter. The nature and biomass of autochthonous bacteria were also important. The solubilization of iron was detected in the upper horizons (L1, 0–30 cm; L2, 30–70 cm; L3, 70–100 cm), where both iron and organic matter are available. Highly significant correlations were found between mineralization of organic matter and iron reduction. Quantitatively, we found that 100 µg of organic C being mineralized could reduce and dissolve 38, 97 and 115 µg Fe2+ in the L1, L2 and L3 horizons, respectively, during 30 days. After 30 days, there was a marked change in the relation, suggesting that lack of iron limited reduction. The coupling of iron reduction to the carbon cycle (soil organic matter biodegradation) is significant.

Notes: Accurate estimates of soil hydraulic properties from other soil characteristics using pedotransfer functions (PTFs) are in demand in many applications, and soil structural characteristics are natural candidates for improving PTFs. Soil survey provides mostly categorical data about soil structure. Many available characteristics such as bulk density, aggregate distribution, and penetration resistance reflect not only structural but also other soil properties. Our objective here is to provoke a discussion of the value of structural information in modelling water transport in soils. Two case studies are presented. Data from the US National Pedon Characterization database are used to estimate soil water retention from categorical field-determined structural and textural classes. Regression-tree estimates have the same accuracy as those from textural class as determined in the laboratory. Grade of structure appears to be a strong predictor of water retention at −33 kPa and −1500 kPa. Data from the UNSODA database are used to compare field and laboratory soil water retention. The field-measured retention is significantly less than that measured in the laboratory for soils with a sand content of less than 50%. This could be explained by Rieu and Sposito's theory of scaling in soil structure. Our results suggest a close relationship between structure observed at the soil horizon scale and structure at finer scales affecting water retention of soil clods. Finally we indicate research needs, including (i) quantitative characterization of the field soil structure, (ii) an across-scale modelling of soil structure to use fine-scale data for coarse-scale PTFs, (iii) the need to understand the effects of soil structure on the performance of various methods available to measure soil hydraulic properties, and (iv) further studies of ways to use soil–landscape relationships to estimate variations of soil hydraulic properties across large areas of land.

Notes: Anion retention is important in highly weathered soils that contain large amounts of iron and aluminium oxides with surfaces of variable charge. Sorption mechanisms retard anionic solute transfer through these soils. We determined the retardation factor for nitrate in highly weathered Ferralsols from New Caledonia from dynamic experiments using a transient-flow method, and we evaluated the effect of soil solution concentration and organic matter content. A simple method with sectionable tubes was used to determine the nitrate isotherm during non-steady-state water flow under unsaturated conditions. The topsoil retarded the movement of nitrate, and the sorption followed a linear isotherm. In subsoils, retardation factors were larger and increased from 1.15 to 2.05 at soil pH as the NO3–-N concentration of the input solution decreased from 71.43 to 0.35 mm, indicative of a non-linear isotherm. Positive surface charge sites were considered to be of two types: one with strong affinity for nitrate at small concentrations and one with weak affinity for adsorption of nitrate at larger concentrations. This type of isotherm with high- and low-energy sites is similar to those found for oxyanions and heavy metals. The related anion exchange capacity was larger than that usually observed in soils of variable charge. Not all exchange sites were detected with our method, and some sites were obviously not available for nitrate retention.

Notes: We present a new method of characterizing the void structures of soils from water retention curves as the primary source of data. The method avoids the problems of other current approaches, which use smoothing curves and can miss the subtleties of soil structure, and usually ignore the shielding of large pores by the small connecting throats surrounding them. In the new method, software we have named ‘Pore-Cor’ is used to generate simple three-dimensional networks of voids that have the same water retention characteristics and porosities as the soils. To find the geometry of the required networks, we have introduced a Boltzmann-annealed simplex which works in four parametric and three Boolean dimensions of parameter space. Also, a more robust measure of the difference between the experimental and simulated water retention curves has been developed. The method is applied to water retention curves for a wide range of English and Welsh soils, both experimental and generated from a pedotransfer function. The resulting simulated void structures have void sizes that change as expected across the soil texture diagram, have different structures as highlighted by the locations of retained water, but have connectivities (number of connecting throats per pore) that vary little. A wide range of other calculations of wetting and non-wetting fluid transport properties, and calculations of the behaviour of fluid-borne pollutants, are now possible. The main bar to further progress is a lack of sufficiently accurate and comprehensive data for water retention, and for saturated and unsaturated hydraulic conductivity.

Notes: Soil contamination by mixtures of petroleum hydrocarbons and heavy metals is common in urban and industrial localities. Interactions between these contaminants have an impact on the mobility and the management of contamination. We have characterized the modifications to the transport of heavy metals (Cd, Cu, Pb, Zn) in soil induced by residual light non-aqueous phase liquid (LNAPL) for two conditions of trapping. Experiments on the elution of tracers and heavy metals in columns of soil were performed with a glaciofluvial material as the soil. Tracer experiments were modelled with the mobile–immobile (MIM) system of partial differential equations. The experiments were designed to compare water flow and metal transport in LNAPL-contaminated soil with a control set. Residual LNAPL was trapped in water-saturated and dry soil to ensure preferential wettability of soil surfaces, namely either water-wet or LNAPL-wet.In water-wet soil columns, LNAPL decreased water flow by two orders of magnitude and increased the fraction of immobile water. Solute residence times (SRTs) suggested that heavy metals resided mainly in mobile water where the reaction time was sufficient to reach steady-state retention. The SRTs also indicated that a fraction of the heavy metal flux diffused to the immobile water where its retention was limited by diffusion. Retention of heavy metals was significantly greater than in the control columns. In LNAPL-wet soil columns, the obstruction of small pores and surface coating by residual LNAPL significantly decreased the attenuation capacity of the soil by decreasing the diffusion of heavy metals to immobile water and surface sites. Evidently, the individual behaviour of heavy metals can be significantly modified by non-miscible organic contaminants. These modifications can have important implications for risk evaluation, contamination management and in situ remediation of soil that is contaminated by mixtures of petroleum hydrocarbons and heavy metals.

Notes: Transport phenomena in porous media depend strongly on three-dimensional pore structures. Macropore networks enable water and solute to move preferentially through the vadose zone. A complete representation of their geometry is important for understanding soil behaviour such as preferential flow. Once we know the geometrical, topological and scaling attributes of preferential flow paths, we can begin computer simulations of water movement in the soil.The box-counting method is used in three dimensions (i.e. cube-counting algorithm) to characterize the mass fractal dimension of macropore networks using X-ray computed tomography (CT) matrices. We developed an algorithm to investigate the mass fractal dimension in three dimensions and to see how it compares with the co-dimensions obtained using the box-counting technique in two dimensions. For that purpose, macropore networks in four large undisturbed soil columns (850 mm × 77 mm diameter) were quantified and visualized, in both two and three dimensions, using X-ray CT. We observed an increasing trend between the fractal dimension and macroporosity for the four columns. Moreover, similar natural logarithm functions were obtained for the four cores by a least squares fit through plots of mass fractal dimension against macroporosity.

Notes: Aminostratigraphy has proved to be a useful approach for dating fossils from the Quaternary. In these studies the amino acids in Quaternary soil formations were determined in an attempt to establish their stratigraphical relationships and relative ages. The sampling sites are in the southwest of Poland, in the Trzebnickie Hills. Three samples of fossil soils and two of recent soils were analysed. The absolute age of the soil samples was estimated by radiocarbon dating. We found that the total amount of amino acids decreased with the increasing age of soil. The smallest amounts of amino acids were found in the oldest fossil soil of Denekamp (Vistulian) age dated 29 600 ± 760 years bp. A sample of recent loess soil contained the most total amino acids, whereas the fossil soil of Lower Atlantic age, dated 3540 ± 230 years bp, was intermediate in respect of the total amount of amino acids, oxidation state and degree of biochemical transformation. Neutral amino acids formed a majority of all the amino acids studied. The method we describe could be useful in relative chronostratigraphical identification of fossil soils.

Notes: In southwest France, much of the forest lands on sandy Spodosols has been converted to continuous maize cropping in the last few decades. To evaluate the impacts of such change on the content and properties of the soil organic matter, we compared the amount of organic carbon and 13C natural abundance in soil and particle-size separates at three locations, selected on the basis of different contents of 0–50 μm particles (clay + silt). After three decades of cultivation, the amount of carbon from the forest pools (Cf) decreased by about 60%, attributable mainly to easily degradable material in sand-sized fractions (−70%). However, a recalcitrant residue remained in soil at a constant proportion, showing that organic matter in these fractions is heterogeneous. Organic matter in the clay + silt fraction was relatively resistant, decreasing by only 20% after 30 years of cultivation. Intensive agricultural management has homogenized the characteristics of the soil and the mineralization of the organic matter, which has resulted in a long-term convergence of organic carbon from the three locations. However, small natural variations in fine particle content were associated with significant differences in the accumulation of carbon in soil. The protective capacity of the soil depended on the proportion of clay + silt fraction, which stabilized the organic matter. Furthermore, the degree of saturation of this fraction with original carbon from forest and its rate of decomposition determined the soil's capacity to accumulate newly added carbon derived from maize.