ALBERT

Notes: The Susunai Complex of southeast Sakhalin represents a subduction-related accretionary complex of pelitic and basic rocks. Two stages of metamorphism are recognized: (1) a local, low-P/T event characterized by Si-poor calcic amphiboles; (2) a regional, high-P/T event characterized by pumpellyite, actinolite, epidote, sodic amphibole, sodic pyroxene, stilpnomelane and aragonite. The major mineral assemblages of the high-P/T Susunai metabasites contain pumpellyite + epidote + actinolite + chlorite, epidote + actinolite + chlorite, epidote + Na-amphibole + Na-pyroxene + chlorite-(-haematite. The Na-amphibole is commonly magnesioriebeckite. The Na-pyroxene is jadeite-poor aegirine to aegirine-augite. Application of empirically and experimentally based thermobarometers suggests peak conditions of T= 250–300C, P= 4.7–6 kbar. Textural relationships in Susunai metabasite samples and a petrogenetic grid calculated for the Fe3+-rich basaltic system suggest that pressure and temperature increased during prograde metamorphism.

Notes: In the Llano Uplift of central Texas (USA), prograde homogenization of garnet growth zoning took place during moderate-to high-pressure dynamothermal metamorphism over a narrow temperature range near the transition from the amphibolite to the granulite facies. This subtle record of early dynamothermal metamorphism survived subsequent static metamorphism at low pressures in the middle-amphibolite facies, despite the destruction of most high-pressure mineral assemblages that originated in the early metamorphic episode. Geographically systematic variations in the degree of homogenization indicate that the uplift as a whole underwent high-pressure metamorphism, in accord with emerging tectonic models for the mid-Proterozoic evolution of the southern margin of the North American continent.

Notes: Chemical disequilibrium exists between all phases of the Alpe Arami garnet-peridotite body (Ticino, Switzerland) which hampers the evaluation of P-T conditions of origin, yet disequilibrium offers the inherent possibility to derive a P-T-t path for this mantle slice. We tried to tackle this problem by carrying out new mineral analyses and taking diffusion rates and bulk-rock compositional effects into consideration. Peak metamorphic conditions from mineral core compositions were estimated as 112050C/50.2 GPa. These values are significantly higher than previously published results and were determined from a combination of the O'Neill & Wood (1979) Fe/Mg garnet-olivine exchange thermometer and the Al-in-orthopyroxene barometer (Brey & Köhler, 1990), and are supported by the Ca/Cr ratios in garnet, which are in accord with these conditions. Details of the exhumation path were derived from (1) rim compositions of minerals that yield a first retrograde stage of 720 50C/2 0.25 GPa (2) a spinel lherzolite assemblage in narrow shear zones (tectonic phase F0″, after Möckel, 1969) which documents a second retrograde stage at 500–600C/0.8-l.5 GPa. The Ca content in olivine (Köhler & Brey, 1989) can be used to evaluate further P-T conditions along the retrograde path. We measured very low values (30–40 ppm Ca) in the cores of olivine and a remarkable increase towards the rim (120 ppm). The low core values may reflect an equilibrium stage during the main Alpine metamorphism. The increasing values towards the olivine rims probably represent a late-stage heating event. The initial cooling rates for the peridotite body are between 2700 and 5100C Ma-1, depending on which diffusion data are used.

Notes: The High Himalayan Crystallines (HHC) of Bhutan were penetratively deformed, intruded by leucogranite and metamorphosed during the collision of the Indian and Asian plates. Metamorphic reaction textures in the HHC show that it experienced decompression while maintaining a laterally heterogeneous, and locally inverted, internal temperature range of c.600–750C. This thermal structure was produced by thrusting hot, migmatitic rocks over lower-grade rocks within the HHC and by the advection of heat from the intrusion of leucogranite dykes and sills during decompression. A variable velocity field within the HHC during exhumation and extrusion between India and Tibet caused the inversion of top to the south sense of shear present throughout most of the HHC to top down to the north shear near its top.

Notes: The Tormes Gneissic Dome (TGD, NW sector of the Iberian Massif, Spain) is a high-grade metamorphic complex affected by a major episode of extensional deformation (D2). The syn-D2 P-T path of the Lower Unit of the TGD was deduced from the analysis of reaction textures related to superimposed fabrics developed during exhumation, analysis of mineral zoning and thermobarometric calculations. It comprises an initial phase of decompression, determined using the tweequ thermobarometric technique, from 6.4–8.1 kbar at 735–750C (upper structural levels) and 7.2 kbar at 770C (lower structural levels) to 3.3–3.9 kbar and 645–680C. This evolution is consistent with the observed sequence of melting reactions and the generation of garnet-and cordierite-bearing anatectic granitoids. The later part of the syn-D2 P-T path consisted of almost isobaric cooling associated with the thermal re-equilibration of the unit in the new structural position. This segment of the P-T path is recorded by assemblages with And + Bt + Ms and Ms + Chi + Ab related to the later mylonitic S2 fabrics, which indicate retrogression to low-amphibolite and greenschist facies conditions.

Notes: Eclogite-grade metamorphism of the Seve Nappe Complex (SNC) in Norrbotten, Sweden, records the attempted subduction of the Baltic continental margin during the early Palaeozoic evolution of the Iapetus Ocean. Metamorphic titanite sampled from several calcsilicate gneisses of the SNC in Norrbotten occurs as part of a prograde, eclogite facies metamorphic mineral assemblage and yields concordant to nearly concordant U/Pb ages of 500–475 Ma. Later structural disruption of these rocks occurred during the Siluro-Devonian Scandian phase of the Caledonide orogeny, but the U/Pb systematics show no evidence of a second generation (metamorphic or recrystallized) of titanite, or of post-Early Ordovician disturbance through Pb loss. Hence the U/Pb ages are believed to record the time of prograde mineral growth during eclogite facies metamorphism of the SNC.These results support earlier Sm/Nd and 40Ar/39Ar studies indicating an Early Ordovician metamorphic age for the eclogitic Norrbotten SNC, and confirm the Early Ordovician destruction of at least this segment of the Palaeozoic passive margin of Baltica. These results indicate that the SNC in the northern Scandinavian Caledonides was subducted and metamorphosed to high grade some 50–70 Myr prior to the high-grade metamorphism of the SNC in the central Scandinavian Caledonides. This result requires significantly different early Palaeozoic tectonic histories for rocks mapped as SNC in the northern Caledonides and those in the central Caledonides, despite a seemingly similar tectonostratigraphic position and broadly similar high-grade metamorphism.

Notes: A suite of garnet-wollastonite-scapolite-bearing calcsilicate granulites from the Eastern Ghats has been investigated to document the controls of mineral reactions during the metamorphic evolution of the deep continental crust. The rocks studied show heterogeneity in modal mineralogy and phase compositions in millimetre-sized domains. Textural relations, and the compositional plots of the phases, established that the clinopyroxene exerts a strong influence on the formation and composition of garnet in the complex natural system. P-T estimates using the vapour-independent equilibria involving garnet define a near isobaric cooling path from c. 850C at c. 5.5–5.2 kbar. The deduced trajectory tallies well with the terminal segment of the overall retrograde P-T path construed from the associated rocks using well-calibrated thermobarometers. The ubiquitous occurrence of wollastonite and scapolite in the main calcsilicate body suggests low aCO2 during peak metamorphic condition. Fluid compositions constrained from mineral-fluid equilibria of the garnet-bearing assemblages show domainal variations as a function of the compositions of the solid phases, e.g. garnet and clinopyroxene. A quantitative log/CO2-log/O2 diagram has been constructed to depict the stability of the different calcsilicate assemblages as functions of the compositions and the behaviour of these fugitive species. The results of the mineral-fluid equilibria and the quantitative fluid/rock ratio calculations, in conjunction with the topological constraints, imply vapour-deficient meta-morphism in the rocks studied. It is argued that fO2 during peak metamorphism was monitored by the ambient fO2. Subsequently, during retrogression, different domains evolved independently, whereas the fluid composition was controlled by the mineral-fluid equilibria.

Notes: The Mallee Bore area in the northern Harts Range of central Australia underwent high-temperature, medium-to high-pressure granulite facies metamorphism. Individual geothermometers and geobarometers and average P-T calculations using the program Thermocalc suggest that peak metamorphic conditions were 705–810C and 8–12 kbar. Partial melting of both metasedimentary and meta-igneous rocks, forming garnet-bearing restites, occurred under peak metamorphic conditions. Comparison with partial melting experiments suggests that vapour-absent melting in metabasic and metapelitic rocks with compositions close to those of rocks in the Mallee Bore area occurs at 800–875C and 〉9–10 kbar. The lower temperatures obtained from geothermometry imply that mineral compositions were reset during cooling. Following the metamorphic peak, the rocks underwent local mylonitization at 680–730C and 5.8–7.7 kbar. After mylonitization ceased, garnet retrogressed locally to biotite, which was probably caused by fluids exsolving from crystallizing melts. These three events are interpreted as different stages of a single, continuous, clockwise P-T path. The metamorphism at Mallee Bore probably occurred during the 1745–1730 Ma Late Strangways Orogeny, and the area escaped significant crustal reworking during the Anmatjira and Alice Springs events that locally reached amphibolite facies conditions elsewhere in the Harts Ranges.

Notes: X-ray diffraction (XRD) patterns from nominally β-SiC specimens often differ from those expected for the cubic crystal structure. These differences include the presence of additional peaks, enhanced background intensities, peak broadening, changes in relative peak heights, and shifts in peak positions. It has long been recognized that they are due to the presence of stacking faults, and models relating the experimental observations to stacking fault population have continued to evolve. The presence and relative magnitude of these features vary among different β-SiC specimens. In this work, computer simulations were used to show that the variations are closely related to differences in the type and spatial distribution of stacking faults in each specimen. In these simulations, stacking sequences were generated using a selectively activated 1-D Ising model with a Boltzmann-type probability function for specifying errors, which allows a wide variety of fault configurations to be generated. Direct correlations between different features in the XRD data to the underlying fault population are demonstrated, which are discussed in this paper. It is also shown that this computer model is general, in the sense that many of the models presented in prior work can be interpreted as limiting cases of it.

Notes: Abstract. Crops grown on virgin upland Vertisols of Zambia, are reported to perform rather poorly. However, subsoiling followed by repeated cultivation over two years apparently improves crop growth. Highest yields were recorded under long-term cultivation (12 years). To evaluate the reasons for these differences in crop response to Vertisol management, physical and hydrodynamic characteristics of soil profiles were studied in three soil management systems. The management systems were: uncultivated or virgin land; land cultivated for two years; and land cultivated for 12 years. The mean soil aggregate size decreased with increased time of cultivation, mostly due to the decrease of the largest sized aggregates. The surface horizon dried more slowly on the long-term cultivation plot. A comparison of the hydraulic conductivities indicated that water intake in the deeper layers improved with increased period in cultivation. Oxygen diffusion measurements showed good aeration at field capacity, to a depth of 0.32m on the long-term cultivation plots, but only to 0.17 m and 0.25 m for 2 years cultivation and virgin plots respectively. Repeated cultivation was beneficial in improving surface soil tilth and in improving subsurface drainage, thus removing the problem of a perched water table which occurred close to the soil surface under natural conditions.

Notes: Abstract. The chemical extractability of heavy metals introduced into the soil during 7 years application of sewage sludge, composted municipal solid waste and sheep manure, and their availability to citrus plants were studied. The total content of metals in the soil (0-20 cm)was increased by the use of sludges and compost, but only the Ni content in the saturation extracts of soil was significantly increased. Total Cd, Cr, Cu, Ni, Pb, and Zn were sequentially fractionated into water-soluble plus exchangeable, organically bound, carbonate-associated, and residual fractions. Most of the heavy metals were present in carbonate and residual fractions, although substantial amounts of water-soluble plus exchangeable Cd, and organically bound Cu and Ni were found. No significant increases in the metal contents in leaves and orange fruits were observed, with the exception of Pb in leaves. Several statistically significant correlations between metal content in plants, metal content in soil fractions, and chemical characteristics of soil were also found.

Notes: Book reviewed in this article: Human impact on Erosion and Sedimentation By D. E. Walling & J.-L. Probst (editors).

Notes: Book reviewed in this article: Soil erosion by water in Africa: Principles, Prediction and Protection By D. Nill, U. Schwertmann, U. Sabel-Koscella, M. Bernhard & J. Breuer.

Notes: Abstract. To provide a practical aid to improving fertilizer practice a mechanistic model was developed that can be readily calibrated for widely different crops. Most of the inputs are easy to obtain and the others, the amounts of fixed soil-K and the velocity constants for fixation and release of soil-K, can be readily measured by a novel procedure which is described.The model calculates for each day the potential increase in plant weight and the increment in root length, from the current plant mass, its %K and pan evaporation. It calculates the maximum amount of K that could be transported through soil to the root surfaces. It modifies this potential uptake by taking account of the ‘feedback’ of plant K on root absorption to give the actual uptake and a new %K in the plant. It calculates the radii of the depletion zones around each root increment and the interchange between the solution, exchangeable and fixed-K in these zones and also in the undepleted regions of soil. Routines are included for the effects of weather on the various processes. Differences between species are accommodated by selecting one of three algorithms for root growth and by adjusting the values of two crop-K parameters that define the decline in a critical and a maximum possible %K with increase in plant mass per unit area.A simplified version of the model runs interactively on the Internet at:

Notes: Abstract. The effect of rate and timing of autumn/winter straw incorporation on the immobilization of spring-applied N-fertilizer are studied. The immobilization of 15N-labelled fertilizer by straw was determined in pot trials with a sandy loam soil (Wick series) collected from two field experiments. In experiment 1, straw was incorporated at four different rates in the autumn; experiment 2 had a fixed rate of straw (7.5 t/ha) incorporated at monthly intervals from September to March. Immobilization in spring was not enhanced when only stubble was incorporated in autumn. However, autumn incorporation of 7.5 t/ha straw resulted in a significant increase in the immobilization of spring-applied N, equivalent to 10 kg/ha; when 15 t/ha straw was incorporated, immobilization increased to 18 kg/ha. The enhancement of immobilization, immediately following fertilizer application, was dependent on the extent of straw decomposition prior to N application. Thus immobilization was related to cumulative thermal time (day °C above 0°C; Tsum between the date of straw incorporation and fertilizer application). Straw which had been incorporated for Tsum 〉 1200 no longer caused appreciable immobilization of spring fertilizer.

Notes: Book reviewed in this article: Erosion and sediment yield: global and regional perspectives Edited by D. E. Walling and B. W. Webb.

Notes: Abstract. The restorative ability of herbaceous (Psophocarpus palustris, Pueraria phaseoloides) and woody (Leucaena leucocephala, Senna siamea, Acacia leptocarpa, Acacia auriculiformis) legume species and of natural regrowth was studied on an eroded and compacted Oxic Paleustalf in southwestern Nigeria. Compared to the control treatment that was continuously cropped for 15 years, four years of fallowing significantly improved test crop yields. However, fallowing with the above species did not substantially improve soil properties, particularly soil bulk density. A longer fallow period may be needed to amend soil physical conditions of this degraded Alfisol. Soil chemical properties were greatly improved following land clearing and plant biomass burning in 1993. However, the residual effect of burning on soil fertility was insignificant in the second cropping year. Among the fallow species, P. palustris and natural fallow showed the best residual effect on test crop performance. Despite the high biomass and nutrient yields of S. siamea and A. auriculiformis, test crop yields on these plots were low due to the border effects from the uncleared and fallowed subplots.

Notes: Abstract. To study the influence of different vegetation species and plant properties on the generation of surface runoff and soil erosion in south east Spain, a series of rainfall simulation experiments was conducted on small (c. 1.5 m2) plots. These were carried out in October 1993 and May 1994 on two sites close to Murcia. Six vegetation types were studied, with some at different stages of maturity, giving a total of nine vegetation treatments and two bare soil treatments. Four replicates of each treatment were exposed to a rainstorm of 120 mm/h for 15 minutes. The results of the experiments show that there are few significant differences in the ability of the vegetation types studied to control runoff or soil erosion. Of the plant properties considered, only plant canopy cover showed a significant relationship with soil loss and runoff with the greatest reduction in soil loss taking place at canopy covers greater than 30%. The implications of this research are that future efforts should be directed at developing ecological successions and revegetation methods which promote a substantial and sustainable canopy cover.

Notes: Abstract. The effect of superficial liming of acidic forest soils on CO2 and N2O emissions and CH4 uptake was investigated with closed chambers in two deciduous and two spruce forests, by weekly to biweekly measurements over at least one year. The flux rates of untreated areas varied between 1.94 and 4.38 t CO2-C/ha per y, 0.28 and 2.15 kg/N2O-N/ha per y and between 0.15 and 1.06 kg CH4-C/ha per y. Liming had no clear effect on CO2 emissions which may change in the long-term with decreasing root turnover and increasing C-mineralization. Apart from one exception, liming resulted in a reduction of N2O emissions by 9 to 62% and in an increase of CH4 uptake by 26 to 580%. The variability in N2O emissions between the forest sites could not be explained. In contrast, the variability of annual CH4 uptake rates could be explained by N content (r2= 0.82), C content (r2= 0.77), bulk density (r2= 60), pore space (r2= 0.59) and pH (r2= 0.40) of mineral soil at a depth of 0 to 10 cm, and by the quantity of material in the organic layer (r2= 0.66). Experiments with undisturbed columns of the same soils showed that between 1 and 73% of the total N2O emissions came from the organic layer. However, atmospheric CH4 was not oxidized in this layer, which represents a diffusion barrier for atmospheric CH4. When this barrier was removed, CH4 uptake by the mineral soil increased by 25 to 171%. These results suggest that liming of acidic forest soils causes a reduction of the greenhouse gases N2O and CH4 in the atmosphere, due to changes in the chemical, biological, and physical condition of the soils.

Notes: Abstract. Agricultural soils, having been depleted of much of their native carbon stocks, have a significant CO2 sink capacity. Global estimates of this sink capacity are in the order of 20-30 Pg C over the next 50-100 years. Management practices to build up soil C must increase the input of organic matter to soil and/or decrease soil organic matter decomposition rates. The most appropriate management practices to increase soil C vary regionally, dependent on both environmental and socioeconomic factors.In temperate regions, key strategies involve increasing cropping frequency and reducing bare fallow, increasing the use of perennial forages (including N-fixing species) in crop rotations, retaining crop residues and reducing or eliminating tillage (i.e. no-till). In North America and Europe, conversion of marginal arable land to permanent perennial vegetation, to protect fragile soils and landscapes and/or reduce agricultural surpluses, provides additional opportunities for C sequestration.In the tropics, increasing C inputs to soil through improving the fertility and productivity of cropland and pastures is essential. In extensive systems with vegetated fallow periods (e.g. shifting cultivation), planted fallows and cover crops can increase C levels over the cropping cycle. Use of no-till, green manures and agroforestry are other beneficial practices. Overall, improving the productivity and sustainability of existing agricultural lands is crucial to help reduce the rate of new land clearing, from which large amounts of CO2 from biomass and soil are emitted to the atmosphere.Some regional analyses of soil C sequestration and sequestration potential have been performed, mainly for temperate industrialized countries. More are needed, especially for the tropics, to capture region-specific interactions between climate, soil and management resources that are lost in global level assessments.By itself, C sequestration in agricultural soils can make only modest contributions (e.g. 3-6% of total fossil C emissions) to mitigating greenhouse gas emissions. However, effective mitigation policies will not be based on any single ‘magic bullet’ solutions, but rather on many modest reductions which are economically efficient and which confer additional benefits to society. In this context, soil C sequestration is a significant mitigation option. Additional advantages of pursuing strategies to increase soil C are the added benefits of improved soil quality for improving agricultural productivity and sustainability.

Notes: Abstract. Field measurement of landfill methane (CH4) emissions indicates natural variability spanning more than seven orders of magnitude, from less than 0.0004 to more than 4000 g/m2 per day. This wide range reflects net emissions resulting from production (methanogenesis), consumption (methanotrophic oxidation), and gaseous transport processes. The determination of an ‘average’ emission rate for a given field site requires sampling designs and statistical techniques which consider spatial and temporal variability. Moreover, particularly at sites with pumped gas recovery systems, it is possible for methanotrophic microorganisms in aerated cover soils to oxidize all of the CH4 from landfill sources below and, additionally, to oxidize CH4 diffusing into cover soils from atmospheric sources above. In such cases, a reversed soil gas concentration gradient is observed in shallow cover soils, indicating bidirectional diffusional transport to the depth of optimum CH4 oxidation. Rates of landfill CH4 oxidation from field and laboratory incubation studies range up to 166 g/m2 per day, among the highest for any natural setting, providing an effective natural control on net emissions. It has been shown that methanotrophs in landfill soils can adapt rapidly to elevated CH4 concentrations with increased rates of CH4 oxidation related to depth of oxygen penetration, soil moisture, and the nutrient status of the soil.Estimates of worldwide landfill CH4 emissions to the atmosphere have ranged from 9 to 70 Tg/y, differing mainly in assumed CH4 yields from estimated quantities of landfilled refuse. At highly controlled landfill sites in developed countries, landfill CH4 is often collected via vertical wells or horizontal collectors. Recovery of landfill CH4 through engineered systems can provide both environmental and energy benefits by mitigating subsurface migration, reducing surface emissions, and providing an alternative energy resource for industrial boiler use, on-site electrical generation, or upgrading to a substitute natural gas. Manipulation of landfill cover soils to maximize their oxidation potential could provide a complementary strategy for controlling CH4 emissions, particularly at older sites where the CH4 concentration in landfill gas is too low for energy recovery or flaring. For the future, it is necessary to better quantify net emissions relative to rates of CH4 production, oxidation, and transport. Field measurements, manipulative studies, and model development are currently underway at various spatial scales in several countries

Notes: Book Reviewed in this article: Phosphorus loss from soil to water: Edited by H. Tunney, O. T. Carton, P. C.

Notes: Abstract. Variously timed sub-optimal irrigation strategies were applied to sugarbeet grown on a light soil (loamy sand or sandy loam) over four seasons (1991 to 1994) to investigate the effect on crop growth and nitrate leaching risk. Data from the two dry seasons, (1991 and 1994) are reported here. In the driest year (1991) soil mineral N levels after autumn harvest were negatively related to crop water use (P 〈 0.05). In this season, there was little drainage from the soil profile, and full irrigation reduced residual soil N by 31 kg N/ha (0-90 cm) compared with the unirrigated treatment (79 kg N/ha). The potential for N leaching during the ensuing winter was consequently more than halved. In 1991 and 1994 there was a strong positive linear relationship between dry matter yield, N uptake and water use, but a negative relationship between plant N concentration and water use. These relationships were a function of the severity and not the timing of drought. The additional N uptake associated with increased irrigation and crop water use was biased towards a large concentration in the aboveground crop (tops), which are normally returned to the soil. The C:N ratio of sugarbeet tops was affected by crop water supply with droughted crops having lower values. This would also influence N release and subsequent leaching risk. However, the effects of drought on N leaching risk were relatively small when compared with other root crops such as potatoes.

Notes: Abstract. The effects of tree crops on the soil physical properties of former agricultural land were compared with those of ley in a rotation with cereals on adjacent sites. Five sites in southern Sweden were investigated focussing on soil water retention characteristics, dry bulk density, macroporosity and saturated hydraulic conductivity. Three of the sites were on light textured soils and two on clay soils. The tree crops were 30 to 35-year-old hybrid aspen, Populus deltoides, and silver birch, Betula pendula, and the ley crops were one to five years old.The light-textured soils under tree crops showed bimodal pore size distributions in the macropore region, whereas under ley crops they showed unimodal distributions. Dry bulk densities were generally smaller and the macroporosities larger under tree crops compared with leyicereal crops. Saturated hydraulic conductivities tended to be larger under tree crops. Slopes of the linear regression lines between saturated hydraulic conductivity and each of the parameters dry bulk density, porosity and macroporosity were steeper in the soil under agricultural crops than under tree crops.Observed differences in physical properties were considered to be an effect of land use, which had brought about changes in aggregate stability, pore size distribution and pore continuity.

Notes: Abstract. Phosphorus concentrations and outputs have been compared and contrasted in six small agricultural catchments in the west and northeast of Scotland. The loss of P from soils to stream waters was more from catchments with intensive dairy cattle farming in the west than from the less intensively stocked/arable catchments in the northeast, with striking differences being seen between the two regions. In the northeast, intensive animal farming caused less P loss in drainage water than arable management.Larger mean annual concentrations were seen in the west (0.076-0.142 mg PO4-P/l as molybdate-reactive phosphate–MRP) compared with the northeast (0.012-0.025 mg PO4-P/l), a feature caused by the combination of limited P-retention in the western Gleysols and smaller inputs to the largely-podzolic northeastern catchments. Stream concentrations were decreased by dilution during winter storm flows and increased during summer baseflow and at the beginning of soil rewetting in autumn.

Notes: Book Reviewed in this article: Freshwater Contamination By B. Webb (editor).

Notes: Book Reviewed in this article: Biotechnical and soil bioengineering slope stabilization. A practical guide for erosion control By D. H. Gray & R. B. Sotir.

Notes: Abstract. This paper reports results from a four year study to investigate the suitability of porous ceramic cups to measure solute leaching on shallow chalk soils. Measurements were carried out in one field following surface applications of nitrate and bromide tracers and in two fields after only bromide was applied. Soil water samples were collected from porous cups at 30,60 and 90cm depth after every 25 mm of drainage, and soil samples from 0–30, 30–60 and 60–90 cm were collected monthly eachwinter. Soil matric suctions andvolumetric moisture content were measured in one winter. Leaching losses, measured with ceramic cups were compared with those measured by soil analysis. Porous cups installed in chalk at 60 and 90 cm depth were only able to collect samples regularly when soil matric suctions were less than 15 kPa. Water held at such low suctions is likely to move quickly through relatively large fissures in the chalk. The slow rate of equilibration between solute concentrations in water moving in macrofissures and those in water moving through micropores of the chalk matrix, means that porous cups may not provide good estimates of leaching losses if they are installed in chalk rock.

Notes: Abstract. Nitrate leaching after one year of a cut grass/clover ley was measured in two succeeding years to investigate how the postponing of ploughing leys from early to late autumn or spring, in combination with spring or winter cereals affected leaching of nitrate. The experiment was conducted as three field trials, two on a coarse sandy soil and one on a sandy loam soil. For calculation of nitrate leaching, soil water samples were taken using ceramic suction cups. The experiments started in spring in a first year ley and ended in spring three years later. Total nitrate leaching for the three year periods for each trial ranged between 160–254 and 189–254 kg N/ha on the coarse sand and 129–233 kg N/ha on the sandy loam. The results showed that winter wheat (Triticum aestivum L.) did not have the potential for taking up the mineralized N in autumn after early autumn ploughing of grass/clover leys, and that the least leaching was generally found when ploughing was postponed until spring, and when winter rye (Secale cereale L.) was grown as the second crop rather than spring barley (Hordeum vulgare L.). Nevertheless, leaching was generally high in the winter period even when winter rye was grown. On these soil types ploughing out should be postponed, whenever possible, to spring. Crop systems that maximize the utilization of mineralized N and thereby minimize nitrate leaching need to be further developed. Based on N balances, the data were further used to estimate the biological N fixation by the clover.

Notes: Abstract. Ceramic suction cups were used to obtain samples of soil solution from permanently grazed swards receiving 200 kg N/ha/y. The suction cups were installed in 1 ha plots at 10, 30 and 60 an depth in a poorly drained, heavy clay soil in S. W. England. The plots were hydrologically isolated from each other by perimeter drains which channelled surface runoff water into v-notch weirs. In one treatment, artificial drainage by a system of field and mole drains also converged to outfalls through v-notch weirs, which enabled samples to be taken. Nitrate and a range of other ionic constituents were examined over a 12 month period in soil solutions taken from the suction cups and compared with leachate obtained from the field drains and surface channels. Field drain samples frequently exceeded the EC limit of 11.3 mg nitrate-N/1, but concentrations in suction cups obtained during the same period did not, and were up to ten-fold less. Although correlations for ions were found between different sampling depths and drainage samples, no clear patterns emerged. It was concluded that suction cups were inappropriate for the determination of the overall leaching losses in this soil type, but provided useful data on changes in ionic concentrations which occurred in different soil horizons through to drainage outfalls.

Notes: Abstract. The impact of soil erosion on soil productivity was estimated for a Rhodic Ferralsol and a Eutric Cambisol in Santa Catarina, southern Brazil. Over equivalent periods, total soil losses were an order of magnitude different (868 and 68 t/ha respectively on the bare soil control), yet the impact on maize yield per tonne of soil lost was far greater at the Cambisol site with less erosion. Similar interesting contrasts between sites were found for the other measures of impact with decline in pH and phosphorus and increase in free aluminium being the most obvious induced soil differences. The results demonstrate the variable nature of erosion impact according to soil type and they highlight the importance of examining a number of measures of impact before pronouncing on the sustainability of any particular agricultural practice.

Notes: Abstract. Mubangwe Farm, northern Malawi, was brought into cultivation from savanna vegetation with Brachystegia between 1970 and 1983 to produce tobacco, maize and groundnuts. Because of poor yields even with inputs of lime, N, P and K the fields were soon abandoned. The soils were only moderately acidic with little likelihood of Al toxicity. They held only small amounts of exchangeable Ca2+ (down to 0.01 cmolc/kg) particularly at depth. Phosphorus availability was low particularly in the subsoil. A minus-one pot experiment showed that the growth of sorghum in topsoil samples was limited by lack of N, P, S and Ca. The lower availabilities of P and Ca in the subsoil are therefore likely to be major limitations to growth, allowing only limited root penetration. The loamy sand to sandy clay soils generally had small available water capacities (down to 0.07 cm3/cm3) which, with restricted root development, may have lead to drought in dry periods during the growing season. The findings emphasize the need to measure both subsoil and topsoil properties when new areas of land are being developed for crop production.

Notes: Abstract. Nitrogen (N) leaching losses from a shallow limestone soil growing a five course combinable croprotation (oilseed rape, wheat, peas, wheat, barley) were measured from 1990 until 1995 using porous ceramic cups, at 60 cm depth, and drainage estimates. The crops were grown with three husbandry systems and two levels of N fertilizer. The husbandry systems were designed to reflect local practice (Standard), the best possible techniques to reduce N loss (Protective) and an Intermediate system which was a compromise between the two. Nitrogen was applied at full and half recommended rates. Drainage started during September in four years and November in one year, with above average drainage in three years. Losses of N were largest after peas (58 kg/ha) and oilseed rape (42 kg/ha), and least (17 kg/ha) before peas sown in spring after a cover crop. Over five years, the Protective management system, which used early sowing and shallow cultivation wherever possible, lost least N (31 kg/ha/y) and the Standard system, with conventional drilling dates and ploughing as the primary cultivation, lost most (49 kg/ha/y). Halving the N fertilizer decreased N loss by 11 kg/ha/y, averaged over the rotation. None of the treatments gave mean drainage water nitrate concentrations of less than 50 mg/l, averaged over the five years. Changes to arable cropping alone will not eliminate the need for other measures to control nitrate concen-trations in public drinking water supplies.

Notes: Abstract. Soil salinity and alkalinity reduce plant production and alter species composition of meadow grasslands in western Jilin Province, China. This study was designed to compare the survival and growth of three grass species (Aneumlepidium chinense, Puccinellia tenuijlora and Hordeum brevisubulatum) transplanted into saline-alkali soils in the field, and to evaluate the effects of gypsum amendments on soil properties and growth of these species. Gypsum treatments decreased soil pH, electrical conductivity, and chloride and sodium levels; water infiltration and calcium levels were increased. Survival of grass transplants was increased by gypsum treatments. Tiller number and height, and grass yields were all increased by the application of gypsum. Improvements in plant growth and survival with gypsum treatment appeared to be due to reduced chloride levels and increased Ca availability in the soil, and to changes in soil structure leading to improved infiltration rates. Revegetation of salinelalkaline soils in this region would be improved by application of gypsum in the range of 14–19 t/ha.

Notes: Abstract. Methane (CH4) is an important greenhouse gas. Flooded rice fields (paddies) are a significant source of atmospheric CH4; estimates of the annual emission from paddies range from less than 20 to 100 million Tg, with best estimates of 50 × 20 Tg. The emission is the net result of opposing bacterial processes: production in anaerobic microenvironments, and consumption and oxidation in aerobic microenvironments, both of which occur sequentially and concurrently in flooded rice soils. With current technologies, CH4 emission from rice fields will increase as production increases. Over the next 25 years rice production will have to increase by 65% from the present 460 Mt/y to 760 Mt/y in 2020. The current understanding of the processes controlling CH4 fluxes, rice growth and rice production is sufficient to develop mitigation technologies. Promising candidates are changes in water management, rice cultivars, fertilization, and cultural practices. A significant reduction of CH4 emission from rice fields, at the same time that rice production and productivity increase at the farm level, is feasible, although the regions where particular practices can be applied, and the trade-offs that are possible, have still to be identified.

Notes: Abstract. Increases in the emissions of globally important nitrogen (N) oxide gases have coincided with significant changes in land use in the tropics. Clearing of tropical forests and savannas for agriculture currently represents the most extensive alteration of land cover on the planet. Over the last several decades, N fertilizer use has increased globally, and in China and the developing world, use has recently surpassed that in the developed world. The potential contribution of land-use change in the tropics to the increase in N oxides is great, yet only a few studies have measured N oxide emissions after tropical land conversion. Our summary of available research shows some conversions to pastures and a few management practices, especially those using N fertilizers, increase emissions beyond those found in undisturbed ecosystems. However, not all studies show unequivocal increases in emissions. Accordingly, we call for a mechanistic understanding of the processes controlling trace gas fluxes to adequately predict under what conditions increased emissions may occur. More measurements are needed to build and test models that may improve management of N fertilizer use in tropical agricultural systems. Given the expected expansion of agriculture and increased use of N fertilizers in the tropics, increased emissions of N oxides from the tropics are likely.

Notes: Abstract. Grazing animals on managed pastures and rangelands have been identified recently as significant contributors to the global N2O budget. This paper summarizes relevant literature data on N2O emissions from dung, urine and grazed grassland, and provides an estimate of the contribution of grazing animals to the global N2O budget.The effects of grazing animals on N2O emission are brought about by the concentration of herbage N in urine and dung patches, and by the compaction of the soil due to treading and trampling. The limited amount of experimental data indicates that 0.1 to 0.7% of the N in dung and 0.1 to 3.8% of the N in urine is emitted to the atmosphere as N2O. There are no pertinent data about the effects of compaction by treading cattle on N2O emission yet. Integral effects of grazing animals have been obtained by comparing grazed pastures with mown-only grassland. Grazing derived emissions, expressed as per cent of the amount of N excreted by grazing animals in dung and urine, range from 0.2 to 9.9%, with an overall mean of 2%. Using this emission factor and data statistics from FAO for numbers of animals, the global contribution of grazing animals was estimated at 1.55 Tg N2O-N per year. This is slightly more than 10% of the global budget.

Notes: Abstract. Increases in the atmospheric concentrations of nitrous oxide (N2O) contribute to global warming and to ozone depletion in the stratosphere. Nitric oxide (NO) is a cause of acid rain and tropospheric ozone. The use of N fertilizers in agriculture has direct and indirect effects on the emissions of both these gases, which are the result of microbial nitrification and denitrification in the soil, and which are controlled principally by soil water and mineral N contents, temperature and labile organic matter.The global emission of N2O from cultivated land is now estimated at 3.5 TgN annually, of which 1.5 Tg has been directly attributed to synthetic N fertilizers, out of a total quantity applied in 1990 of about 77Tg N. This amount was 150% above the 1970 figure. The total fertilizer-induced emissions of NO are somewhere in the range 0.5-5 Tg N. Mineral N fertilizers can also be indirect as well as direct sources of N2O and NO emissions, via deposition of volatilized NH3 on natural ecosystems and denitrification of leached nitrate in subsoils, waters and sediments.IPCC currently assume an N2O emission factor of 1.25 ± 1.0% of fertilizer N applied. No allowance is made for different fertilizer types, on the basis that soil management and cropping systems, and unpredictable rainfall inputs, are more important variables. However, recent results show substantial reductions in emissions from grassland by matching fertilizer type to environmental conditions, and in arable systems by using controlled release fertilizers and nitrification inhibitors. Also, better timing and placement of N, application of the minimum amount of N to achieve satisfactory yield, and optimization of soil physical conditions, particularly avoidance of excessive wetness and compaction, would be expected to reduce the average emission factor for N2O. Some of these adjustments would also reduce NO emissions. However, increasing global fertilizer use is likely to cause an upward trend in total emissions even if these mitigating practices become widely adopted.

Notes: Abstract. The validity of the model described in Greenwood & Karpinets (1997) was tested against the results of single year, multi level K fertilizer experiments. Measurements of plant mass, %K in the plant and K activity ratio in soil had been made at harvest and at intervals during the growing season on spring wheat, summer cabbage and turnips. Reasonably good agreement was obtained between these measurements and simulated values when the two ‘crop’ parameters (defining the dependence of critical and maximum possible %K on plant mass) were adjusted for each crop. Also good agreement was generally obtained for plant weight and plant %K at harvest in less detailed experiments on 10 other crops. Values of the two ‘crop’ parameters for 12 of the crops were strongly correlated with one another suggesting that a single ‘crop’ parameter may be all that is required to define most inter-species differences in plant-K demand.Simulations with the model indicate that, in central England, no response of 10 crops to K fertilizer would be likely on soils containing more than 170 mg of 1 M ammonium nitrate extractable-K/kg of soil and having clay contents of between 15 and 45%. Shortcomings of the model and opportunities for advance are discussed.A simplified version of the model runs on the Internet at:

Notes: Abstract. As part of a study of recession farming on the ‘fadama’ lands on a segment of the Komadugu-Yobe floodplain, a survey was carried out to investigate the local farmers’ perception of soil types and management practices. The farmers are clearly aware of the differences in soil type on the fadama and they possess unique skills in managing their farm lands. The farmers classify fadama soils for recession farming by assessing soil texture and soil drainage conditions by feel and observation. Integrating such local knowledge into soil surveys will lead to better practical definition of mapping units and give soil names that have more meaning for the farmers.

Notes: Abstract. The large boreal peatland ecosystems sequester carbon and nitrogen from the atmosphere due to a low oxygen pressure in waterlogged peat. Consequently they are sinks for CO2 and strong emitters of CH4. Drainage and cultivation of peatlands allows oxygen to enter the soil, which initiates decomposition of the stored organic material, and in turn CO2 and N2O emissions increase while CH4 emissions decrease. Compared to undrained peat, draining of organic soils for agricultural purposes increases the emissions of greenhouse gases (CO2, CH4, and N2O) by roughly 1t CO2 equivalents/ha per year. Although farmed organic soils in most European countries represent a minor part of the total agricultural area, these soils contribute significantly to national greenhouse gas budgets. Consequently, farmed organic soils are potential targets for policy makers in search of socially acceptable and economically cost-efficient measures to mitigate climate gas emissions from agriculture. Despite a scarcity of knowledge about greenhouse gas emissions from these soils, this paper addresses the emissions and possible control of the three greenhouse gases by different managements of organic soils. More precise information is needed regarding the present trace gas fluxes from these soils, as well as predictions of future emissions under alternative management regimes, before any definite policies can be devised.

Notes: Abstract. The projected increase in sewage sludge used on land within many countries in the European Community will provide a major source of entry for several heavy metals into the soil. Although the application rate of sewage sludge to agricultural land is constrained by maximum annual additions of heavy metals, there is a need to know the sensitivity of those soils to heavy metal inputs which are physically suited for application. A rulebased classification using weighted parameters designed to assess the metal binding capacity of soil and the risk of groundwater pollution has been applied to soils data held within the Macaulay Land Use Research Institute's National Soils Inventory The classification uses soil pH, organic matter content, texture and soil colour as a surrogate for iron oxide concentration. The results indicate that some metals, for example cadmium and zinc are potentially more mobile in soils than others such as lead, but that the majority of soils display a strong or very strong binding capacity for all the metals. However this pattern can only be sustained if the soil pH values are maintained at their present values; a fall of one pH unit marks a dramatic shift towards the weak and moderate binding classes. The approach is largely unvalidated but does provide a useful framework for incorporating our mechanistic understanding of processes into wide area soil quality assessments and in identifying future research opportunities.

Notes: Abstract. Kriging is used to provide detailed quantitative information for a range of soil characteristics across the floodplain of the River Gambia. Application of spatial statistics to a large area with a coarse grid of data points produces spurious patterns unless the area is first partitioned into soil-geomorphic mapping units, each of which has a unique pattern of spatial variation. Even combining classical soil survey method with spatial statistics, the large short-range variability of acid sulphate soils means that single factor maps conceal a large element of uncertainty. A more robust procedure is to map the probability of occurrence of critical values of key characteristics.

Notes: Abstract. Field experiments undertaken at 14 sites, on a range of soil types, in lowland England, during the cropping years 1989–1993, tested the effectiveness of cattle or pig slurry as a source of nitrogen for cereal cropping. Slurry was applied in autumn, winter and spring, to autumn and spring sown cereal crops. Assessments included slurry nitrogen efficiency relative to N in spring applied fertilizer in terms of both grain yield and grain protein production, apparent crop recovery and content of mineral nitrogen in soil profiles. Crop response to nitrogen was poor at seven sites where high residues of soil mineral nitrogen (SMN) were present. On the seven responsive sites, spring slurry applications proved more efficient (mean 40%) as a source of N than autumn (mean 24%) or winter applications (mean 32%). These differences were smaller than reported in a number of other studies, probably as a result of relatively low excess winter rainfall, resulting in less nitrate leaching during the period of the investigation. Rapid incorporation into the topsoil of slurry applied in autumn, increased (28 kgN/ha) the SMN of samples taken early in the winter. However this increase did not lead to a consistent improvement in crop N uptake. Slurry dressings, whenever applied, can be expected to make a significant contribution to the N requirement of the succeeding crop and need to be taken into account when calculating the appropriate spring fertilizer application.

Notes: Abstract. Soils in areas with high livestock density contribute to the eutrophication of aquatic ecosystems through loss of nutrients, especially phosphorus (P). In order to identify the potential for P loss from such soils we determined phosphorus extracted by water (H2O-P), by double lactate (DL-P), and P sorption capacity (PSC) and degree of P saturation (DPS) in soil samples from two counties, one with low (Harle-catchment) and the other with very high livestock density (Vechta). Both catchments are hydrologically connected with the tidal areas of the North Sea.The mean concentrations of H2O-P (0.4mmol/kg) and DL-P (3.9 mmol/kg) were lower in the Harle-catchment than in the Vechta area (1.2 mmol/kg, 6.8mmol/kg). Although oxalate-extractable Al (Alox) and Fe (Feox) and the derived PSCs varied according to soil type and to land use, the livestock density and the resulting high concentrations of oxalate-extractable P (Pox) were shown to be the main reason for the very high DPS of up to 179% in the county of Vechta. These values exceeded DPS reported from other intensive pig feeding areas in western Europe and indicate the potential for significant P loss. Less than 40% of the variation in Pox could be explained by the routinely determined H2O-Por DL-P. Geostatistical analyses indicated that the spatial variability of Pox depended on manurial history of fields and Alox, showed still smaller-scale variability. These were the major constraints for regional assessments of P losses and eutrophication risk from agricultural soils using available soil P-test values, digital maps and geostatistical methods.

Notes: Abstract. Although gypsiferous soils cover approximately 100 million ha in the world, it is only in the past two decades that their pedogenic and agronomic properties have been better understood and their classification improved. There is still no method to assess adequately their production potential.This paper focuses on gypsum accumulation forms as diagnostic criteria for a rapid soil suitability appraisal in the field. Pseudomycelia, gypsum spots, powdery coatings and other localized in situ precipitations usually indicate soils with less than 15% gypsum. Depending on their intensity and depth of occurrence in the root zone, they define a soil environment which is suitable for semi-sensitive and semi-tolerant crops. Continuous gypsum accumulations characterize soils or horizons with high (e.g. more than 25%) gypsum contents, and these can be used only for tolerant crops.The land use potential of gypsiferous soils is primarily determined by: (a) the depth of the impermeable layer, (b)the gypsum content within the root zone, and (c) the crop tolerance level. A method is proposed to assess the land suitability of gypsiferous soils on the basis of these criteria.

Notes: A standardized dataset of derived soil properties for the 106 soil units considered on FAO-UNESCO's 1:5 million scale Soil Map of the World is presented. It was derived from a statistical analysis of the 4353 soil profiles held in the WISE (World Inventory of Soil Emission) database, which was developed at the International Soil Reference and Information Centre (ISRIC) for the geographic quantification of soil factors that control processes of global change. Median values are presented by soil unit for selected soil properties including: pH(H2O); organic carbon content; cation exchange capacity; sum of exchangeable Ca2+, Mg2+ and K+; exchangeable sodium percentage; bulk density; total porosity; available water capacity; soil drainage class; and gravel content class. Medians for these variables are presented both for the topsoil (0–30 cm) and subsoil (30–100 cm), where applicable. The data set can help to refine ratings for soil quality in global environmental models pending the availability of comprehensive georeferenced databases on soil and terrain resources such as SOTER, the World Soil and Terrain Database. In a Geographical Information System (GIS) it can be linked to the units shown on the digital Soil Map of the World through the legend code.

Notes: Abstract. The effect of grazing pressure on infiltration, runoff, and soil loss was studied on a natural pasture during the rainy season of 1995 in the Ethiopian highlands. The study was conducted at two sites with 0–4% and 4–8% slopes at the International Livestock Research Institute (ILRI) Debre Zeit research station, 50 km south of Addis Ababa. The grazing regimes were: light grazing stocked at 0.6 animal-unit-months (AUM)/ha; moderate grazing stocked at 1.8 AUM/ha; heavy grazing stocked at 3.0 AUM/ha; very heavy grazing stocked at 4.2 AUM/ha; very heavy grazing on ploughed soil stocked at 4.2 AUM/ha; and a control with no grazing. Heavy to very heavy grazing pressure significantly reduced biomass amounts, ground vegetative cover, increased surface runoff and soil loss, and reduced infiltrability of the soil. Reduction in infiltration rates was greater on soils which had been ploughed and exposed to very heavy trampling. It was observed that, for the same % vegetative cover, more soil loss occurred from plots on steep than gentle slopes, and that gentle slopes could withstand more grazing pressure without seriously affecting the ground biomass regeneration compared to steeper slopes. Thus, there is a need for developing ‘slope-specific’ grazing management schedules particularly in the highland ecozones rather than making blanket recommendations for all slopes. More research is needed to quantify annual biophysical changes in order to assess cumulative long-term effects of grazing and trampling on vegetation, soil, and hydrology of grazing lands. Modelling such effects is essential for land use planning in this fragile highland environment.

Notes: Abstract. An effective fertilizer recommendation system requires information on seasonal, soil-related and cultural variations in soil mineral nitrogen (N) and nutrient requirements of the crop. This can be provided by dynamic N turnover models, such as listed by Plentinger & Penning De Vries (1996). In this paper, we describe a survey of farmer opinion designed to ascertain what farmers want from such a decision support system. Over 100 farmers were surveyed. Surveyed farmers requested that default values be available for all model inputs. Inputs should be entered both by windows-based menu (for clarity) and tabular format (for speed), have user-selected units, and be fully supported by context-sensitive help. The system should have a hierarchical structure allowing access to fixed parameters, and be compatible with commonly used farm recording packages. Recommendations should be provided both for the field (single and optional application rates), and in tabular format across the whole farm. Simulations should be easily rerun using more recent crop and weather data. Turnover processes underlying recommendations should be illustrated by flow diagrams of flux between pools, pie charts of fertilizer fate, bar charts of movement down the soil profile and graphical plots of changes in N status against time.

Notes: Abstract. Ten chalk topsoils (0-25 cm) were repacked into columns in the laboratory. After leaching similar to one year's throughflow in the field, loss of K was equivalent to between 9 and 74kg K/ha. This represented between 3 and 30% of the initial exchangeable K with which loss was poorly correlated. Loss was dependant on the soil solution concentration and was inversely proportional to potassium buffer power.The loss of magnesium in the same columns was between 10 and 22 kg Mg/ha (6-21% of the initial exchangeable Mg). Magnesium loss was poorly correlated with exchangeable Mg.When KCl fertilizer was incorporated into the soils, the increase in leaching of potassium was 1–35% of the K addition. Application to the top of the column resulted in less leaching than when the K was incorporated. Leaching of magnesium was increased by up to 5 kg Mg/ha.Potassium leaching may be delayed by the underlying A/C horizon but pure chalk, with an extremely low buffer power for K, has little ability to retain K. Extremely calcareous topsoils were the most leaky although in practice it is the organic chalk soils on which it is most difficult to attain adequate K levels. On all chalk soils, maintenance of a high K level with K fertilizer is likely to cause unnecessary long-term leaching losses. Annual, rather than biennial, fertilizer applications are to be preferred.

Notes: Abstract. The effects of straw disposal by burning and incorporation on soil and crop nitrogen (N) supply, were investigated on two light textured soils in central (ADAS Gleadthorpe) and eastern England (Morley Research Centre) over the period 1984 to 1995. Nitrogen balance calculations showed that after 11 years of contrasting straw incorporation versus burn treatments, the cumulative N returns in straw were c. 570kg/ha at Gleadthorpe and c. 330 kg/ha at Morley However, these N returns via straw incorporation were not reflected in increased total soil N levels in autumn 1994. There were no differences (P 〉 0.05) between straw disposal treatments in autumn soil mineral N supply, readily mineralizable N or organic carbon. Similarly, there were no consistent differences between the treatments in terms of crop yield, crop N uptake or optimum fertilizer N rates. Fertilizer N applications of 200 kg N/ha/y increased topsoil organic carbon from 1.18 to 1.28% and total N content from 0.091 to 0.102% on the loamy sand textured soil at ADAS Gleadthorpe, but not at Morley. Previous fertilizer N applications increased the quantity of nitrate-N leached in drainage water by c. 20 kg/ha at Gleadthorpe and c. 60 kg/ha at Morley overwinter 1994/95, and by 10–20 kg/ha at both sites overwinter 1995/96. There was some indication overwinter 1994/95 that straw incorporation reduced nitrate-N leaching by 10–25 kg/ha, but there were no differences between treatments overwinter 1995/96.

Notes: Abstract. Formulation of nitrogen balances on farms requires accurate information on all inputs of the nutrient. N2-fixation by legumes, particularly forage legumes, is an important input which is difficult to measure. Simple regression models have been established from the literature for predicting N2-fixation by grass–white clover (Trifolium repens) mixtures using dry matter yields.Linear relationships were obtained between the N2- fixation (Nfix) and the extra dry matter production of mixed swards (Md) compared with pure grass swards. Nitrogen fixation was given by Nfix= A + 0.067Md where A is the intercept having a value of 6.8 for cut swards and -168.1 for grazed swards. A common slope was adopted because the F statistics showed that slopes fitted separately were not significantly different. The value of the negative intercept represents the supply of N to the grazed sward from soil and excreta-derived N. The regression equation for the cut sward gave reasonable predictions (r2= 0.953) of values of N2-fixed for experimental data not used in establishing the relationship. For grazed grass, the approach over-estimated the N2- fixation by an average of 15%.

Notes: Book reviewed in this article: Agricultural Recycling of Sewage Sludge and the Environment By S. R. Smith.

Notes: Book reviewed in this article: No-tillage seeding: science and practice By C. J. Baker, K. E. Saxton & W. R. Ritchie.

Notes: Abstract. The rates of CO2 production and decomposition of 13C-enriched Lolium perenne leaves and roots in soil from the surface five cm of two upland stagnohumic gley soils were measured in laboratory experiments. One of the soils had been limed (pH 6.8) 13 years earlier. The other was unlimed (pH 3.7). Liming increased the rate of CO2 release from soil to which no L. perenne had been added. About 30% of the 13C in L. perenne leaves remained in both limed and unlimed soil after 224 days. By contrast, less 13C-remained in the limed soil amended with L. perenne roots (44%) than in the limed soils (55%). Although the daily rate of CO2 from the plant material-amended soils was initially greater in the improved than in the unimproved soil, it subsequently declined more rapidly.

Notes: Abstract. The characteristics and variability of soils within a 30 ha experimental site in N. E. Nigeria are analysed in relation to tree establishment. Profile description and analyses for some 480 surface samples of the sandy to clayey surface soils from Lake Chad lacustrine sediments provide baseline properties against which any subsequent modifications resulting from agroforestry practices can be assessed and to which initial tree performance can be related. This has been undertaken using principal component and spatial analyses. Inherited soil properties show spatial variations across the site which can be related to the soil textural parameters. The initial survival of trees planted for agroforestry experimentation shows strong correlations with the inherited characteristics of the soil rather than with acquired soil properties.

Notes: Abstract. Field measurements of cumulative infiltration and of the matric potential prior to infiltration were made with double-ring infiltrometers and tensiometers, respectively, on two sandy loams in north-east Scotland. The time to ponding for constant-rate infiltration was also measured in the same infiltrometers by applying water at a constant rate until ponding commenced. Under the range of initial potentials studied (-2 to - 17 kPa), an exponential relation was adequate to describe the relation between sorptivity and initial matric potential. The time to ponding was also strongly dependent on initial matric potential and increased dramatically as the soil became drier. Measurements of time to ponding were in good agreement with values predicted from the theory of Clothier et al. (1981) using values for sorptivity and the A parameter obtained from the cumulative infiltration experiments. Measurements and predictions clearly showed the importance of the sorptivity versus initial matric potential relation in controlling the time to ponding of such sandy soils. These results have implications for determining the generation of runoff and the establishment of stream flows, as well as determining optimum rates and design of irrigation.

Notes: Abstract. Use of either three or six occasions to spread similar total amounts of slurry was investigated over the late winter/early spring period in two years, on plots with underdrainage. Slurry was spread on four 7 m by 25 m plots which were instrumented to allow collection of drainflow and runoff. The ‘mobile water’ pore space allowed transport of a small proportion of applied slurry through the 0.75 m soil profile. Evidence of a polluted ‘mobile water’ pulse occurred after periods of up to 48 hours following spreading, suggesting subsurface rather than overland flow. Timing of the pulse depended on whether subsequent rainfall accelerated the flow The contaminated flow persisted for 6–12 hours. The worst contamination of 39 mg/l NH4+ -N occurred under ‘bypass flow’ conditions, when 52 mm of rain fell during the 48 hours after a 5.2 mm application. Two contributory factors appeared important. The first was the long duration of the high intensity storm and the second was an extended period of severe frost believed to have created fissures associated with frost heave. Making several applications of slurry in amounts less than 35 m3/ha is preferable to fewer larger applications during spring, for cereals on medium to heavy soils. This recognises the likelihood of there being underdrainage on arable land and the optimal use of well-drained, partially frozen ground to avoid compaction by slurry tankers.

Notes: Abstract. When Albania emerged from its seclusion in 1991, the scientific community had its first opportunity to interact with its international counterparts. Soil resource assessment was made with systems developed in the early 1950s, laboratory facilities to provide supporting data were poor, and it was recognized that a new assessment was urgently needed.The country faces a major challenge in reforestation and soil conservation against a background of overgrazing by sheep and goats and clearing of trees and scrubs for fuelwood. Even orchard and olive trees were used as fuelwood during the winters of 1990 and 1991. Since then, gully and rill erosion has accelerated on many of the sloping lands. In addition to reforestation and conservation measures to reduce the pressures on the sloping land, it is necessary to enhance productivity on the fertile valley bottom soils where most of the agriculture is confined. In the recent past, grain yields have declined due to reduced fertilizer use (low purchasing capacity), and poor management practices. More recently productivity has slowly improved, but land degradation, particularly erosion, has visibly increased.USDA Natural Resources Conservation Service in collaboration with the Land Resources Institute of Albania, initiated work on a new national soil map through collation of existing information and field studies. The land unit for land use planning, evaluation, and general management decisions, is the Major Land Resource Area (MLRA). Each MLRA encompasses geographically associated soils, the majority of which have broadly similar patterns ofclimate, water resources, and land uses. The MLRAs presented here are based on the soil map of Albania at 1 : 200 000 scale. The MLRA information provides an overview of the landscape and natural resources. It can be used to assess land suitability for various crops, opportunities to achieve self sufficiency in food production, selection of areas for both field crops and highvalue crops for export, and identification of appropriate farming system technologies. Each MLRA will have a set of degradation processes which can be flagged, therefore each of them becomes a unit for decision making with respect to investments in research and mitigating technologies. The task is far from complete. Appropriate databases are needed to support the decisions that are being made at national level. To complement the MLRA and related database, decision support systems are needed for the important task of developing policy options.

Notes: The binding of metal to humic substances is problematical. The approaches for studying metal binding to organic matter are briefly reviewed. Ion-selective electrodes (Cu2+ and Pb2+) were used to measure metal complexation by a whole peat and an extracted humic acid (HA) fraction. Scatchard plots and calculation of incremental formation constants were used to obtain values for the binding constants for the metals onto both peat and HA. Both the peat and the humic acid had a larger maximum binding capacity for Pb2+ than for Cu2+ (e.g. at pH = 5 HA gave 0·188 mmol Cu2+ g−1 and 0·564 mmol Pb2+ g−1: peat gave 0·111 mmol Cu2+ g−1 and 0·391 mmol Pb2+ g−1). Overall, the humic acid had a larger metal binding capacity, suggesting that extraction caused conformational or chemical changes. The binding constants (K1) for Cu2+ increased with increasing pH in both peat and humic acid, and were larger in the peat at any given pH (e.g. at pH = 5 HA gave log K1= 2·63, and peat gave log K1= 4·47 for Cu2+). The values for Pb2+ showed little change with pH or between peat and humic acid (e.g. at pH = 5 HA gave log K1= 3·03 and peat gave log K1= 3·00 for Pb2+). In the peat, Cu2+ may be more able to bind in a 2:1 stoichiometric arrangement, resulting in greater stability but smaller binding capacity, whereas Pb2+ binds predominantly in a 1:1 arrangement, with more metal being bound less strongly. Whole peat is considered to be more appropriate than an extracted humic acid fraction for the study of heavy metal binding in organic soils, as this is the material with which metals introduced into an organic soil would interact under natural conditions.

Notes: Excess salts may be removed from soil by leaching, but ponding water on the soil's surface and allowing infiltration requires large quantities of water. During such leaching water flows preferentially through macropores between aggregates, while the flow within aggregates is much less. Consequently, solute within aggregates is removed much more slowly, thus decreasing overall leaching efficiency. For this reason intermittent ponding can be more efficient because it allows time for solute to diffuse to the surfaces of aggregates during the rest period and subsequently be removed in macropore flow. We explored solute transport in aggregated soils under intermittent leaching in three ways: theoretically, by laboratory experiments on columns of porous ceramic spheres as analogues of aggregates, and by simulation. Solute movement during displacement is described by the mobile-immobile convection-dispersion equation. During the rest period flow ceases, and solute redistributes within the aggregates by diffusion, the key variable being the effective diffusion coefficient, De of the solute in the aggregates, and longitudinally by diffusion within macropores (though this was ignored in the simulation). We estimated De for our porous spheres from observations of solute outflow into finite volumes of stirred distilled water. The theory was validated against experiments on saturated columns for different aggregate-size distributions, flow velocities, and displacement and rest periods, with most parameters estimated independently. Experiments and simulations showed that water savings of 25% were possible under our laboratory conditions, increasing as aggregate size, flow velocity and duration of rest period increased. The potential of intermittent leaching in the field is considered.

Notes: Comparisons were made between the phenolic and carbohydrate signatures of soil profiles developed under grass, spruce and ash stands. Samples were collected from a brown earth soil which was originally under the same land use, but over the past 43 years has supported different monocultures. Distinct signatures associated with each litter type were recorded in individual profiles. A relatively undecomposed phenolic fraction from lignin and hydrolysable carbohydrate fraction from plants had accumulated in the soils under spruce and ash. This largely reflected the quantity and quality of the litter inputs from the spruce and ash compared with the grass. The phenolic and hydrolysable carbohydrate fractions accounted for as much as 60% of the total organic carbon concentration in the deep horizons. In the grassland profile both fractions were more decomposed than under ash and spruce suggesting that the forest profiles had rapidly accumulated a carbon pool with a comparatively slow rate of decomposition. This was most apparent from the spruce profile (which contained 398 mg g−1 C carbohydrate hydrolysed using trifluoracetic acid (TFA) in the C horizon compared with 165 and 45 mg g−1 C under ash and grass respectively). We conclude that the decay rate of these fractions is a function of the vegetation type.

Notes: Fractal dimensions were used to quantify the complex geometry of soil cracking patterns. Two fractal dimensions were measured to provide an adequate description of soil cracks: the mass fractal dimension, DM (which provides a measure of crack heterogeneity) and the spectral dimension, d (which provides a measure of crack connectivity). The cracking patterns generated by four soils were compared and related to their textural characteristics. As the clay content of the soil increased (6·1%–24·3%), so did DM (1·29–1·43), and d (1·03–1·33). Correlations indicated that there was a significant (P 〈 0·01) linear relation between the soil's clay content and the DM and d of cracks, the correlation coefficients obtained being equal to 0·965 and 0·840, respectively. Significant correlations (P 〈 0·01) were also observed between structural stability indices of the soil and the fractal dimensions of its cracks, increases in the stability of the soil, particularly of the clay fraction, being associated with cracks with greater fractal dimensions.

Notes: The relation between physical and mechanical responses and the structure of clay has been studied. Deformation in response to mechanical stress was measured on samples of Wyoming mont-morillonite and Saint Austell kaolinite in solutions of NaCl (0·005; 0·05; 0·5 and 5 M). Salt concentration was expressed in terms of osmotic potential of water and loading in terms of envelope pressure potential of water, and deformation was measured precisely under small mechanical stress. During shrinking and swelling, deformation was small and reversible, and consolidation was related to the largest mechanical stress applied previously in its history. The arrangement of the clay at equilibrium depends foremost on the type of clay mineral and physico-chemical properties of the liquid phase. For Na-montmorillonite suspensions, transition between gels with tactoids and rigid media with quasicrystals is abrupt and occurs at a potential of about −2000 J kg−1, whether the stress is osmotic or mechanical. Swelling indexes obtained under osmotic and mechanical stress are of the same order of magnitude. Deformation of smectite results from modifications of interassemblage and intra-assemblage organization.

Notes: We have developed a critical state, stress-strain analysis that predicts the entire sequence of states from start to the end of a constant cell volume triaxial test in p-q-v-ɛz, space, where p is the spherical stress, q is the deviator stress, v is the specific volume and ɛz is the axial strain. The analysis requires five soil properties to be specified, these being the critical state properties (M, λ and κ) and two elastic properties (any two of E, η, G and K—all four can be found from any two).In order to test the analysis, properties taken mostly from one series of constant cell volume triaxial tests are used to simulate the behaviour in a second test series. In both series the two soils (a sand loam and a clay loam) were tested at several different water contents. The first (property estimation) series of tests was performed using large samples, whereas the second (verification) series involved small samples. The behaviour is quite different in the two series. The elastic property E was not determined in the first series of tests but was estimated from the second series. Furthermore, for three very wet samples, λ had to be estimated by fitting the analysis to the data. The verification was not therefore fully independent of the input test data, particularly for the three wet samples. The stress strain analysis simulated the behaviour of both series of tests in all four dimensions of the p-q-v-ɛz space. The match in p-q-v space was good for all samples. On a q-ɛz plane, the value of q was under-estimated for several samples, but for most of the samples the match was good on this plane. The analysis was generally as good as, and sometimes better than, a previous analysis that deals only with the end point of the test in p-q-v space. The previous analysis did not take account of the elastic properties. The stress-strain analysis therefore seems to offer a useful framework for parameter estimation from constant cell volume triaxial tests. This extends the usefulness of the test itself, as the elastic properties may now be accounted for. The success of the analysis also strengthens the record of success of the critical state concept for unsaturated soils.

Notes: Measurements of N uptake by rice plants growing in a puddled flooded soil and the corresponding changes in soil solution NH: concentrations and the soil NH: diffusion coefficient are used to calculate how far root uptake properties and transport to the roots limit acquisition of N by rice. With root uptake parameters assigned values such that influx was maximal within realistic ranges, the minimum root length densities required to explain uptake were similar to measured root length densities in both N-fertilized and unfertilized soil. This suggests that most if not all of the root length was active in uptake and that uptake per unit root length was near maximal. A sensitivity analysis showed that the necessary minimum root length is very sensitive to root uptake properties within appropriate ranges. Transport to the roots was mainly by diffusion. Rates of diffusion will generally not limit uptake in well-puddled soils, but they may greatly limit uptake in puddled soils that have been drained and re-flooded and in unpuddled flooded soils. Uptake of fertilizer N broadcast into rice field floodwater and absorbed by roots in the floodwater or soil near the floodwater is not likely to be limited by root uptake properties or transport.

Notes: The derivation of pore size distributions from the soil water retention characteristic is complicated by the influence of the connectivity of the pore space on drainage. We examine this issue in the context of a random fractal pore network model. A two-dimensional one-parameter model simulates the drainage of water from an initially saturated pore network, explicitly accounting for the complex pore interactions which exist over a range of scales within the network. A parameter range is identified over which pore connections significantly hinder the advance of air into the network. The results demonstrate that connectivity between pores in a random structure can affect the drainage to an extent that in general it is not possible to obtain an accurate measure of the pore size distribution from the water retention data. These results, together with findings based on closely related multiscale network models, show that one should use with caution water retention models derived from fractal structures and based solely on pore size distributions.

Notes: The recent addition of trivalent metals to soil and their subsequent movement within the biosphere are of concern. For this reason, the sorption of chromium (Cr), yttrium (Y). rhodium (Rh), lanthanum (La), praseodymium (Pr) and gadolinium (Gd) in two contrasting acid soils has been determined. Except for Rh, the sorption of the other trivalent metals conformed well to the Langmuir equation with derived sorption parameters similar for all the trivalent species tested. Calculation of the buffer powers indicated that under both small (0·01 mmol kg−1) and large (1 mmol kg−1) trivalent metal soil loadings 〉 99·5% of the metals will be associated with the exchange phase with small quantities present in the bulk soil solution (〈0·5%). It seems that the slight availability of metals within the bulk soil solution will slow the rate of trivalent metal bioremediation of contaminated sites.

Notes: Compositional differences between soil solutions obtained by different methods have frequently been reported; variations in the soi1: solution ratio may explain these results. In this study we compared the amount and composition of phosphorus (P) in soil leachates and soil solutions from a temperate grassland soil in northeast Scotland and determined the influence of soi1:solution ratio on P fractions in soil water extracts. Leachates were collected from intact soil cores over 6 months, the cores were then destructively sampled, and soil solutions obtained by centrifuging. Molybdate reactive P (MRP) represented 71% of the total dissolved P (TDP) in soil leachates but only 54% in soil solutions. The MRP component in soil water extracts increased from 71% to 92% as the soi1:solution ratio increased from 1:15 to 1:15·4, while the dissolved organic P (DOP) component decreased from 26% to 6%. As the soil:solution ratio increased the amount of MRP extracted increased; by contrast the amount of DOP and dissolved condensed P (DCP) extracted remained constant. While the MRP component is regulated by soil sorption processes, the supply and amount of DOP and DCP is probably related to biological activity. Dissolved organic carbon (DOC) extracted at wide soi1:solution ratios contained a smaller proportion of P than that extracted at narrower ratios. The results indicate differences in the behaviour of P fractions in the soil at various soi1:solution ratios and that these are reflected in the P composition of soil solution and leachate.

Notes: In a pre-alpine meadow in the Toggenburg (Switzerland), casts of the earthworm Aporrectodea nocturna, initially detected 20 years ago around a newly planted hedge, now extend 170 m from the hedge. The abundance of A. nocturma decreased between 140 and 170 m from the hedge from 237 (site: An+) to 0 (site: An−) individuals m−2. The worm's activity and the macroporosity it has created have been studied using CAT scanning followed by automated image analysis of pores from 1·5 to 9 mm diameter. Brightness values in images from CAT scanning showed distinct local frequency maxima for stones, soil matrix and macropores. Measured diameters of pores were strongly linearly correlated with diameters of needles used to produce artificial pores. Pores from 1·5 to 3 mm were most abundant. The maximum number of pores from 1·5 to 9 mm (about 1600 m−2) was larger than the maximum number of all earthworms (about 480 m−2). Modelling the cast production of A. nocturna indicated that 23·8 kg m−2 were deposited on the soil's surface within 3 months. The measured macroporosity (1·5–6 mm) was one-quarter to one-sixth of the pore volume corresponding to the removed casts. Thus, net production of pores by earthworms was a result both of the burrowing activity and of the refilling with eroded cast material. Depth distributions of bulk density, total porosity and pores from 1·5 to 9 mm were different at An+ from those at An−. However, diffusion of butane was equal at An+ and An−. Three-dimensional reconstruction suggested that the disposition (continuity, interconnectivity) of pores was more important for gas diffusion than the structure (size distribution, frequency) and bulk soil parameters.

Notes: Humic acids from six Brazilian topsoils (three Latosols and three Podzols) and five soil fungal melanins were hydrolysed and the released amino sugars qualitatively and quantitatively determined by capillary gas-liquid chromatography. Melanins were obtained from liquid culture media, synthesized with nitrate or asparagine as a source of N, of Stachybotrys atra, Aspergillus glaucus, Eurotium echinulatum and Hendersonula toruloidea. Glucosamine (48–60%), galactosamine (39–52%), and traces of mannosamine were detected in all humic acids. The total amino sugar content ranged from 1351 to 2287 mg kg−1. In the fungal melanins analysed, mostly glucosamine (80–99%) and trace to small amounts of galactosamine and mannosamine (〈10%) were found in amounts ranging from 192 to 635 mg kg−1. The Occurrence of mannosamine in fungal melanins and fungal polysaccharides had not previously been found. The present study gives additional data to the theory that fungal melanins may play a role, as precursors, in the formation of soil organic matter.

Notes: We investigated dissolved organic matter (DOM) from soil, sewage sludges, water from waste disposal sites, and composts as sorbents and potential carriers for hydrophobic polycyclic aromatic hydrocarbons (PAHs) in soil. Partition coefficients (expressed log KDOC) for two 5-ring compounds were 4·8–4·9 for DOM from soil, 4·5–47 from composts, and 4·3–4·4 from sewage sludges. The DOM from compost and sewage sludge can influence the transport of non-ionic organic contaminants because of the large concentrations of dissolved organic carbon (DOC) released from these materials. Leachates from waste disposal sites did not sorb PAHs. The DOM from compost contained a large percentage of organic molecules 〉 14 000 Da (32–46%), whereas DOM from waste disposal leachates contained only 7-lo%, and so bound less PAHs. The percentage of total hydrophobic components, as characterized by XAD-8 chromatography, was 50 ± 9% for most of the DOM solutions and did not express the differences in affinity of the organic sorbents to PAHs in the same way as the KDOC values. Isolated molecular-weight fractions of DOM from composts sorbed benzo(k)fluoranthene in each fraction. The log KDOC values were 4·1–4·3 for both fractions, 〈 1000 and 1000–14 000 Da, and 4·8–5·0 for the fraction 〉 14 000 Da. The interaction of PAHs with DOM 〈 1000 Da cannot be explained by partitioning within intramolecular nonpolar environments of dissolved macromolecules; rather it seems to be due to the amphoteric properties of DOM. This type of interaction of PAHs with small DOM molecules might affect the mobility of hydrophobic organic chemicals in soils.

Notes: La stabilityé de la structure des horizons de surface et de profondeur de sols ferrallitiques du Congo est étudiée en fonction du mode de gestion des terres et de la teneur en carbone organique total des échantillons. Le rôle du carbone soluble à l'eau chaude dans l'agrégation est appréciéà partir de deux approches expérimentales, impliquant des extractions après chauffage en étuve ou en autoclave. Pour ce faire, des comparaisons sont faites entre les taux des macroagrégats stables (〉200 pm) à l'eau froide et à l'eau chaude. Les résultats indiquent que les situations culturales étudiées induisent des variations significatives des teneurs en carbone total. Le taux des macroagégats stables à l'eau froide est très fortement corrélé aux teneurs en carbone total et en carbone solubiliséà l'eau chaude. Toutefois, les taux des macroagrégats stables obtenus avant et après extraction du carbone à l'eau chaude ne sont pas significativement différents, ce qui peut remettre en question les résultats sur la fonction agrégeante des matières organiques solubles, déduits des seules approches statistiques.Hot-water soluble organic matter and aggregate stability. Methodological aspects and application to ferrallitic soils of the Congo〈section xml:id="abs1-2"〉〈title type="main"〉SummaryThe structural stability of surface and deeper horizons of ferrallitic soils of the Congo was studied in relation to the land use and the total organic carbon content of the samples. The role of hot-water soluble carbon in aggregation was assessed with two experimental approaches, one by heating in an oven and the other in an autoclave under pressure. The proportion of aggregates (〉 200 μm) stable in cold water were compared with that of macroaggregates stable in hot water. Cropping situation sunder study induced significant variations in total carbon content. Aggregate stability was highly correlated with both soluble and total carbon contents. However, amounts of water-stable aggregates obtained before and after solubilization of organic matter in hot water were not significantly different. This result would infirm the supposed aggregating role of soluble organic matter, inferred from statistical data only.

Notes: Soil can affect human health in several ways leading either to specific diseases or to more general ill health. Some illnesses are caused by people's eating soil (geophagia), or by their inhaling it which can lead to malignancy if the soil contains asbestiform minerals; pathogens in the soil can lead to tetanus and infestations of hookworm, and particles may enter the body through abrasions and cause a form of elephantiasis. Radon from the soil is implicated in some cancers, and poorly drained soil has been linked recently with infant mortality. Most examples of ill health associated with the soil are caused by concentrations of elements in food or water that are either deficient or toxic. These elements include aluminium, arsenic, cadmium, copper, fluorine, iodine, lead, selenium, thallium and zinc. Their concentrations might reflect the natural condition of the soil, or the effects of people's actions, such as pollution. In isolated subsistence communities that grow their own food, distinct relations between elements and the aetiology of diseases can be identified. Examples include Keshan disease caused by selenium deficiency, and itai-itai disease caused by excess cadmium. Some of the relations between soil and health are uncertain and the causes putative, and they require further research to validate them. They include the association of heart disease with poor acid soil, as in the glaciated regions of northern Europe and the coastal plain of the eastern United States of America. Even for well-defined relations it is evident that many are more complex than was originally thought, however, and greater understanding will require multidisciplinary investigation.

Notes: Soil compaction is a concern worldwide, particularly where compactible soils are used for intensive agriculture in a wet climate. We have investigated the impact of compaction and the associated changes in soil structural qualities on crop production and environmental pollution. The overall objective was to develop soil management systems that provide suitable conditions for crop growth and minimize environmental damage. We ran large-scale field experiments studying the preservation of structural quality in arable and permanent grassland, using management systems such as the control or elimination of field traffic and the application of conservation tillage and zero tillage. We measured bulk density, shear strength, cone resistance, macroporosity, relative diffusivity, air permeability and water infiltrability to identify soil qualities that could be used for selecting suitable soil management. Along with crop yield, we measured environmental impacts, such as the emissions of nitrous oxide from the soil, which require the interaction of soil structure and water content near the soil surface. Soil structure influenced wetness, which affected trafficability, compaction and nitrogen retention. Measurement of properties that affect fluid storage and transport, such as macroporosity, provided soil quality indices that helped in recommending suitable soil management systems. Spatial variation of structure associated with wheel-track locations could be estimated rapidly using a cone penetrometer. Variation was particularly important in determining crop yield consistency. Crop productivity and soil structural qualities were preserved best when field traffic was eliminated. A reduced ground-pressure system successfully minimized compaction in grassland but was less effective in an arable rotation. Unless traffic is eliminated, good timing of operations is the most effective way to preserve soil structural quality.

Notes: Summary A clear understanding of the short-term decomposition and fate of crop residues is necessary to predict the availability of mineral N in soil. The fate of 13 C15N-labelled wheat straw in a silty soil (Typic Hapludalf) was studied using particle size fractionation and in situ incubation in which the equivalent of 8 t dry matter per ha of straw was incorporated into the soil over 574 days. Soil samples were separated into five particle-size fractions by wet sieving after disruption of aggregates. The weight, C and N contents, and 13C and 15N atom excess of each fraction were determined. Straw-derived C disappeared rapidly from the 〉 2000-μm fraction with an estimated half-life of 53 ‘normalized’ days (equivalent of 10°C and −0−01 MPA water potential). Straw-derived C appeared to be only temporarily stored in the intermediate fractions (1000–2000 and 200–1000 pm). The maximum net 13C accumulation in the 50–200-μm fraction was 4·4% of added 13C. Straw-derived C accumulated most rapidly and preferentially in the 50-μm fraction, which stabilized after 265 days and accounted for 70% of the residual 13C on day 574. Although there was more residual 15N than 13C, the distributions and kinetics of the two isotopes in the fractions were similar.

Notes: The amounts of aluminium liberated from a proto-imogolite (P-I) sol by 1–3 mM oxalate at pH 4·8–7·1 are found to be in excellent agreement with those calculated on the basis of the solubility product of the P-I sol, and the stability constants for aluminium oxalate complexes established earlier. Calculated solubility curves are presented for proto-imogolite sols in the presence of 10−3, 10−4 and 10−5 M total oxalate over the pH range 4–8, and also for the case where oxalate concentrations are controlled by solid calcium oxalate in the presence of 0·05, 0·5 and 5 mM calcium ion. We conclude that the presence of a proto-imogolite allophane in podzol B horizons of pH 5·0 requires oxalate concentrations less than 10−5 M. For fertile agricultural soils with typical calcium concentrations (approximately 5 mM) in the soil solution, aluminium oxalate concentrations would be limited by calcium oxalate solubility to less than 10−6 M in the presence of proto-imogolite allophane at pH values exceeding 5·5. In leached podzolic soils calcium concentrations are generally less than 0·05 mM, and would not limit the formation of aluminium oxalate complexes.

Notes: The rate of hexavalent chromium reduction by a soil humic acid (SHA) was investigated in aqueous solutions where concentrations of Cr(VI), H+, and SHA were independently varied. Rate experiments were done with a large excess of SHA over Cr(VI). Rates of reduction depend strongly on [H+], increasing with decreasing pH. Typical Cr(VI)-SHA reactions display a nonlinear reduction of Cr(VI) with time that cannot be modelled with simple first- or second-order rate equations. An empirical rate equation is developed for Cr(VI)-soil humic acid reactions over a range of experimental conditions. The model is in part based on a reactive continuum concept developed for soil fulvic acids. The rate equation describing Cr(VI) reduction by SHA is: R= -(k0+k[H+]1/2)[HCrO4−]1/2Xe−1,where k0 is (8·3 ± 1·2) × 10−12, s−1k is (2·04 ± 0·05) × 10−9 l1/2 mol−1/2 s−1, and Xe is the equivalent fraction of SHA oxidized. The rate equation adequately models Cr(VI) reduction in an experiment with [Cr(VI)]0 four times greater than the maximum concentration used in its derivation. Cr(VI) reduction at pH 3 by two other SHAs can also be modelled using the rate equation. The difference between the rate coefficients for the humic acid and the fulvic acid from the same soil was greater than the difference in the rate coefficients for humic acids from different soils.

Notes: Phosphate sorption by calcareous soils has been studied mainly on heavily fertilized agricultural soils and soils with calcite as the main carbonate mineral. We examined factors affecting phosphate adsorption in the soils of a semi-arid, mediterranean, dolomitic, soil and vegetation chrono-sequence in southeastern Spain. The youngest soils are highly eroded, Sandy Regosols (Typic Xerorthents) under gorse-scrubland vegetation. These have small P sorption capacities, large Mg-Ca carbonate contents but small amounts of Fe and Al oxides. Small total P (HNO3/HClO4 digestion) concentrations (30–130 μg P g−1), of which up to 90% is Ca-bound (HCl-extractable), are typical of these young soils. P sorption markedly increased when Ca2+ was added to the solution. The fractionation of previously sorbed P indicates that the fate of most of this extra-sorbed P is the labile-P fraction sorbed on to (carbonate) surfaces and the apatite-like fraction (NaHCO3-extractable and HCl-extractable fractions). At the other extreme, older more-intensively weathered, sandy-clay-loam rendzinas (Entic Haploxerolls), supporting dense mature garrigue, have a much greater P adsorption capacity and larger clay and Fe and Al oxide concentrations. They have more total P (ca 400 μg P g−1), much of it in occluded form (residual fraction). These soils show no significant differences in P sorption whether or not CaCl2 was used as a background electrolyte. Considering the overall variations within the chronosequence, dithionite extractable Fe and Al are the properties best correlated with P sorption. This support the general finding that crystalline Fe-oxides (e.g. goethite and haematite) appear to be the most important P-sorbing component for soils in the Mediterranean region, rather than amorphous Fe-oxides (e.g. ferrihydrite) as is reported for more mesic areas. Stepwise multiple regression and fractionation data, however, suggest that, provided the soil solution is rich in Ca2+, carbonate may also be a significant contributing factor to P sorption, especially in the youngest of these dolomitic soils.

Notes: Non-exchangeable K always contributes to some degree to plant nutrition. To understand this contribution and to deduce a predictive buffer power model the release and fixation of K was studied on a range of 44 calcareous clay soils. Short-term K sorption and desorption experiments (16 h) were followed by the measurement of soil exchangeable K (ammonium acetate extraction). Soil K-Ca exchange properties and the contributions of exchangeable K and non-exchangeable K to K dynamics of the soil-solution system were estimated. The change in the amount of non-exchangeable K during the experiment was generally proportional to the initial constraint imposed to the soil-solution system (ø), i.e. the solution: soil ratio multiplied by the difference between the solution K concentration imposed at the beginning of the experiment and the solution K concentration for which neither sorption nor desorption of K would occur. The proportionality coefficient (β) called the 'soil ability for K release and fixation’ was identical for release and fixation for 36 soils, whereas eight soils showed some difference between their ability for fixation and their ability for release of K. When β was considered identical in the release range and in the fixation range for all soils it was inversely proportional to the initial K saturation ratio of the CEC corrected for the amount of ammonium extractable K which was not in exchange equilibrium with Ca. This quantity of ammonium extractable K which is not in equilibrium with Ca probably contributes only partially to plant nutrition. For the studied soils this quantity contributed a large proportion of exchangeable K (26–65%) especially in soils with a small K content. Due to the contribution of non-exchangeable K to soil-solution K dynamics the buffer power of the system does not only depend on exchange properties but also on soil release and fixation properties. When β was taken into account buffer power was better estimated than when it was deduced from ion exchange alone.

Notes: The controlled release of agrochemicals from capsules, uniformly distributed in the soil, and their spread in the soil profile by diffusion and convection, coupled with first-order degradation, are studied theoretically. This transient transport is formulated mathematically as an approximate description of two simultaneous processes: (1) local release from the capsule, described as taking place in a confined, spherical soil domain, with a quasi-steady-state diffusional spread in each time step and (2) the vertical spread of the released material in the soil profile, described by the convection-dispersion equation including a source term for the solute transport, coupled with the Richards’ equation for the water flow. These processes of release, spread and degradation are simulated for realistic field conditions to study the effects of management practices and environmental conditions on the release rate. For a given amount of chemical per unit area, the rate of release increases with increasing number of capsules and with increasing depth of incorporation. Increasing irrigation intensity also enhances the release rate, as well as increasing the time interval between irrigations for the same seasonal amount of water applied. Under a given irrigation regime and incorporation practice, the rate of release increases progressively from coarse to fine-textured soils. The amount of released agrochemical remaining in the target zone after a certain time is compared with the amounts of a similar non-encapsulated agrochemical and of an inert tracer retained in the soil. The encapsulated material always persists longer, to an extent depending on the above-mentioned conditions.

Notes: Regression is frequently abused in soil research. Its proper use is for statistical prediction. It may also be used to calculate equations for calibration A regression equation may be used to express a functional relation between two soil variables that are thought to be dated by some simple mathematical law but only where one of the variables is known exactly. In most other circumstances regression is inappropriate. Where departures from a functional relation are a result of errors of measurement and sampling fluctuation it should be replaced by a structural analysis to find the best equation. Where the underlying relation is truly bivariate it should be described as such.

Notes: The hardening of soils containing little clay content has often been related to the cementing of skeleton grains. In sandy-loam soils from the southern plain of the Chad basin the skeleton grains of the hard horizon are coated and bonded by wall-shaped bridges. We have studied the bonding agent by X-ray diffraction on extracted fractions (〈 0·5 pm) and by quantitative in situ electron microprobe analysis on thin sections. The coatings and the wall-shaped bridges are composed mainly of SO2 (mean = 60%), Al2O3 (29%) and FezO3 (7%). The TiO2 and K2O contents were small (1–2%), and the MgO, Na3O and CaO contents were less than 1%. The composition of the coatings and the wall-shaped bridges is almost homogeneous, even if the Si/Al atomic ratio varies weakly with the morphology of the bridges. The bonding agent constituting the coatings and the wall-shaped bridges seems to be a mixture of predominantly Al-Fe beidellite with small contents of kaolinite, illite and quartz. A small content of fine clay minerals plays the major role of bonding agent and is responsible for hardness in sandy or sandy-loam soils.

Notes: Books reviewed in this article.Marshall, T. J., Holmes, J. W. and Rose, C. W. Soil Physics.Baize D. and Girard M.-C. (eds) Référential Pédologique 1995.Jabiol, B., Brêthes, A., Ponge, J.-F., Toutain, F. and Brun, J.-J. L'humus sous toutes ses formes.Collins, M. E., Carter, B. J., Gladfelter, B. J., and Southard, R. J. (eds) Pedological Perspectives in Archaeological Research.Magdoff, F. R., Tabatabai, M. A. and Hanlon, E. A. (eds) Soil Organic Matter: Analysis and Interpretation.

Notes: We have analysed the differences in infant mortality for 1981 to 1990 in areas of contrasting soil types in south-central England. The soils overlie rocks of varied lithology and hydrology, ranging from porous and permeable Chalk and limestones, to the generally wet and impermeable Oxford and Lower Jurassic Clays. The study area comprises 504 administrative wards, for each of which the soil has been classified as being predominantly‘Wet’, ‘ Intermediate’ or ‘Dry’, depending on the degree of seasonal or periodic waterlogging. The soil classes used are those mapped by the Soil Survey of England and Wales and relate closely to the underlying geology. We find proportionately more infant deaths on the‘Wet’ soils, and a gradation towards lower infant mortality rates on the drier soils. Overall, infant mortality on the‘Wet’ soils is 31·9 percent greater than on the‘Dry’ soils, for reasons that remain unexplained. This relation between infant mortality and soil moisture remains after the effect of social class has been removed.

Notes: Surface crusting results from aggregate breakdown under raindrop impact. It reduces the infiltration rate and may induce erosion by increasing runoff. Soil crustability and erodibility generally increase as organic carbon content decreases. Samples of topsoil were collected from fields cropped continuously for maize after land clearance at various dates. Organic carbon content ranged 4–30 g kg-1. Aggregate stability was assessed by measuring fragment size distribution after different treatments. Samples were also subjected to simulated rainfall. The size of fragments forming the seal when the rain ceased and the infiltration rate during the rainfall were measured to characterize seal structure and hydraulic properties. Development of the seal and infiltration capacity were related to aggregate stability, which was itself a function of organic carbon content. The relations between aggregate breakdown, crusting and infiltration enabled us to predict soil physical behaviour from measurements of aggregate stability which are easier to make than direct measurements under rainfall. The proposed tests offer the opportunity to evaluate actual or potential soil physical degradation and erosion risks without extensive field measurements.

Notes: Analytical modelling of the movement of water through porous solids consisting of more than one homogeneous layer is a problem in soil science and in construction engineering. In this paper equations based on the Green and Ampt model describe the absorption of water into a two-layer composite bar for the cases of absorption through a material of large sorptivity into one of smaller sorptivity and vice versa. These predictions are compared with experimental results. There is broad agreement between theory and experiment at all times. We conclude that the absorption of water into a two-layer composite is ultimately controlled by the second material in the absorbing sequence irrespective of whether this material has the larger or the smaller sorptivity.

Notes: Eight samples of goethite ranging in surface area from 18 to 132 m2 g-1 were mixed with phosphate at a range of pH values for periods which ranged from 0·5 h to 6 weeks. The sample with a surface area of 18 m2 g-1 had been hydrothermally treated to improve its crystallinity. Its rate of reaction with phosphate depended on pH but was complete within a day. Its maximum observed reaction was close to the theoretical maximum for surface adsorption of 2·5 μmol m−2. For the other samples, phosphate continued to react for up to 3 weeks and exceeded the value of 2·5 μmole m−2. The duration and extent of the reaction depended on the crystallinity of the goethite. The results were closely described by a model in which the phosphate ions were initially adsorbed on to charged external surfaces. The phosphate ions then diffused into the particles. This was closely described using equations for diffusion into a cylinder.Samples of goethite which had been loaded with phosphate dissolved more slowly in HCl, and had a longer lag phase, than phosphate-free goethite. For the hydrothermally treated goethite, HCl removed much of the phosphate when only a small proportion of the iron had been dissolved. For a poorly crystallized goethite, it was necessary to dissolve much more of the iron to obtain a similar removal of phosphate. Brief treatment with NaOH removed most of the phosphate from the hydrothermally treated goethite but only half the phosphate from a poorly crystallized goethite. These results are consistent with the idea that phosphate ions were not only bound on external surface sites but had also penetrated into meso- and micro-pores between the domains of the goethite crystals and were then adsorbed on internal surface sites. This penetration tied the domains together more firmly thus increasing the lag phase for dissolution. Differences between sites for phosphate adsorption are therefore caused mainly by their location on either external or internal sites. Models that ignore this are incomplete.

Notes: Incorporation of labelled 15N and 14C amino acids and nucleic bases into soil humus fractions as well as humus turnover was investigated under field conditions. The dynamics of 15N and 14C incorporation into organic matter was characterized by the following main steps: rapid incorporation of the labelled substance prevailing for the first 1–3 weeks, and decomposition of included labelled fragments prevailing beyond one month after substance addition. The annual turnover rates of N and C in humus fractions due to incorporation of amino acids and nucleic bases were calculated. The turnover rate of N in humus is two to three times that of C. The contribution of amino acids to organic matter generation is about twice as great as that of nucleic bases and other N-containing organic substances. This indicates the important role of amino acids in the humification process and humus turnover. Turnovers of humic acids (0·002 year−1 for C and 0·02 for N) are the most rapid of humic fractions investigated, and humin is characterized by the slowest turnover (0·0002 year−1 for C and 0·007 for N). There are no significant differences in the turnover rates of fulvic acid fractions (0·0002 year−1 for C) with different molecular weight.

Notes: As the acidity of rain diminishes, changes in the pH, ionic strength, and ion activities of the soil solution will influence the charge characteristics of soil. We have investigated the response of cation exchange capacity (CEC) of three acid forest soils of variable charge to small changes in pH, ionic strength, and SO2−4 concentration. The variable charge for these temperate soils has the same significance as for tropical soils and those from volcanic ash. Maximum absolute increase in CEC on increasing pH by 0·2–0·5 units reached 5 cmolc kg-1 in O horizons. The increase in CEC on doubling ionic strength in EA and Bsh horizons of a Cambic Podzol was about half that amount, but relative gains compared to effective CEC were 65 and 46%, respectively. For other soil horizons, absolute changes were smaller, and relative changes were between 10 and 30%. Halving the SO2−4 concentration significantly influenced CEC only in some samples. Both pH and ionic strength must be adjusted with care when determining CECc of acid forest soils. Decreasing acid deposition will not inevitably increase CECc because in some soils pH effects may be balanced by simultaneous decrease in ionic strength.

Notes: Books reviewed in this article.Thomas, M.F. Geomorphology in the Tropics. A Study of Weathering and Denudation in Low Latitudes. John Wiley and Sons, Chichester.Robert, M. Le sol: Interface dans 1 'environnement, ressource pour le diveloppement.Chhabra, R. Soil Salinity and Water Quality. A.A. BalkemaSchiechtl, H.M. and Stern, R. (Barker, D.H., ed.) Ground Bioengineering Techniques for Slope Protection and Erosion Control.Skipper, H.D. and Turco, R.F. (eds) Bioremediation: Science and Applications.Orlov, D.S. Humic Substances of Soils and General Theory of Humification.Powlson, D.S., Smith, P. and Smith, J.U. (eds) Evaluation of Soil Organic Matter Models Using Existing Long Term Datasets.Wagenet, R.J. and Bouma, J. (eds) The Role of Soil Science in Interdisciplinary Research.Bonham-Carter, G.F. Geographic Information Systems for Geoscientists: Modelling with GIS.

Notes: Although trade element uptake on and release from solid phases are fundamental controls on the migration of the elements in the environment, the controls are incompletely understood. The extraction of uranium from two soils, both of which have been labelled naturally with uranium, was therefore studied using a cation resin exchange technique. One soil was a peat from the Needle's Eye natural analogue site, Scotland, and the other was a calcareous brown earth from Derbyshire, England. The effects of different exchanging cations, solution pH and the presence of complexing anions (Cl−, CO32−, SO42−) in solution on uranium extraction were assessed. The extraction could be described by a simple, first-order kinetic model with up to three rate constants being identifiable in individual experiments. In both soils no single reaction pathway appeared to dominate, and extraction was slow, with rate constants of 10−3−10−4 h−1 in acid conditions and around 10−6 h−1 in neutral conditions. Half-times for uranium release in the experiments were in the range 30–60 days in acid and around 10 years in neutral conditions; in the field they are therefore expected to be several years at both sites. Incorporation of kinetic factors into a simple one-dimensional migration model illustrates that their overall effect is to retard migration. Ideally, therefore, reaction rates should be taken into account in predictive modelling of element transport.

Notes: Various soil texture schemes are in current use. These differ in the size ranges of their particle fractions. There is a need to establish simple methods to correlate these conventional schemes. Therefore I have defined closed-form exponential and power law functions to fit models to cumulative particle-size distribution data. I have tested the functions for their suitability (i) to represent cumulative particle-size distribution curves and (ii) to transfer data between distributions that differ in the size ranges of the particle fractions. I found that closed-form exponential functions adequately represent the cumulative particle-size distributions of fine-textured soils (clay, silty clay, silty clay loam, clay loam, silt loam and loam texture), whilst closed-form power functions better describe the cumulative particle-size distributions of coarse-textured soils (sand, loamy sand, sandy loam, sandy clay and sandy clay loam texture). The functions defined are found to be suitable to transfer data between different texture schemes. The use of this approach is illustrated by examples of data transformations between three widely used soil texture schemes: ISSS, Katschinski's and USDA.

Notes: The measurement of unsaturated soil hydraulic properties is expensive and time consuming. These properties are hence frequently predicted with so-called pedo-transfer functions (PTFs) using basic soil properties (e.g. particle-size distribution, organic matter content and bulk density). In this study PTFs are developed by regression between hydraulic data and basic soil properties. Parameters are quantified for: (i) the retention model of van Genuchten using 80 soil profiles with a total of 230 retention curves, and (ii) the conductivity model of Gardner using 20 soil profiles and 129 hydraulic conductivity curves. The profiles represent the main soil families in Portugal, ranging from coarse sands to heavy clays. The PTFs derived from data for all soils provide a fairly poor description of the hydraulic parameters because of the heterogeneity of the profiles. The description of several parameters is improved by using PTFs that are developed for more homogeneous soils grouped according to their particle-size distribution. A further improvement is achieved by including the water contents at 2·5 cm, 100 cm, and 15 000 cm water suctions in the retention PTFs, or the saturated hydraulic conductivities in the conductivity PTFs.