ALBERT

Notes: Soil minerals are known to influence the biological stability of soil organic matter (SOM). Our study aimed to relate properties of the mineral matrix to its ability to protect organic C against decomposition in acid soils. We used the amount of hydroxyl ions released after exposure to NaF solution to establish a reactivity gradient spanning 12 subsoil horizons collected from 10 different locations. The subsoil horizons represent six soil orders and diverse geological parent materials. Phyllosilicates were characterized by X-ray diffraction and pedogenic oxides by selective dissolution procedures. The organic carbon (C) remaining after chemical removal of an oxidizable fraction of SOM with NaOCl solution was taken to represent a stable organic carbon pool. Stable organic carbon was confirmed as older than bulk organic carbon by a smaller radiocarbon (14C) content after oxidation in all 12 soils. The amount of stable organic C did not depend on clay content or the content of dithionite–citrate-extractable Fe. The combination of oxalate-extractable Fe and Al explained the greatest amount of variation in stable organic C (R2 = 0.78). Our results suggest that in acid soils, organic matter is preferentially protected by interaction with poorly crystalline minerals represented by the oxalate-soluble Fe and Al fraction. This evidence suggests that ligand exchange between mineral surface hydroxyl groups and negatively charged organic functional groups is a quantitatively important mechanism in the stabilization of SOM in acid soils. The results imply a finite stabilization capacity of soil minerals for organic matter, limited by the area density of reactive surface sites.

Notes: Organo-mineral associations stabilize soil organic matter, though the mechanisms by which they do so are unclear. We used particle-size fractions 〈 6.3 μm of two soils to examine the importance of Fe oxides, short-range order Al silicates and the surface areas of minerals and micropores on the formation of organo-mineral associations. In the subsoil Fe oxides were most strongly statistically correlated with the mineral-bound organic carbon. We therefore assume that they are the most important substrates for the formation of organo-mineral associations. There is no indication that this is caused by physical protection of organic matter in their micropores (〈 2 nm). In the Haplic Podzol, dithionite–citrate–bicarbonate-soluble short-range order Al silicates may also play a role. Fe oxide particles were calculated to offer specific surface areas of ∼ 200 m2 g−1 (goethite) and ∼ 800 m2 g−1 (ferrihydrite), corresponding to crystal diameters of only a few nm. We assume that the resulting large amount of oxide-specific reactive surface sites (conditionally charged hydroxyl groups) is responsible for their dominant role as sorbents. With maximum C loadings of 1.3 mg C per m2 Fe oxide for the Dystric Cambisol and 1.1 mg C per m2 Fe oxide + short-range order Al silicates for the Haplic Podzol the subsoils of both soils seem to have reached saturation with respect to organic matter sorption. In contrast to subsoil horizons, organo-mineral associations from topsoils contain much larger amounts of organic matter. Here a larger C loading on Fe oxides or a greater importance of other sorbents in addition to the oxides must be assumed.

Notes: If biospheric sinks, such as soil organic carbon, are to be used to meet obligations for greenhouse gas emission reduction under the Kyoto Protocol, the permanence of these sinks needs to be considered. Further, since only direct human-induced carbon sinks can be included, and sinks resulting from indirect and natural effects cannot be used, there is a pressing need to separate direct human-induced effects from indirect and natural effects. Since these effects also influence the permanence of soil organic stocks, this paper attempts to synthesize existing knowledge in soil science, and use models to examine the likely influence of direct, indirect and natural effects on the permanence of soil organic carbon stocks.

Notes: The formation of basic aluminium sulphate (BAS) minerals [(K,Na)nAlx(OH)y(SO4)z] has often been invoked to explain sulphate retention in soils. These minerals have not yet, however, been directly observed in the soil. We extracted the clay fractions of Andosols intercepting large inputs of volcanogenic sulphur dioxide and acids (HCl, HF), simply by dispersing clays with Na+-resins in deionized water without any other chemical treatment. Clay fractions concentrate 39–63% of total sulphur content of soil. Transmission electron microscopy coupled with energy-dispersive analysis revealed the presence of BAS particles, appearing as nodules and spheres. These particles have an equivalent diameter smaller than 0.2 µm. They have an Al:S ratio close to 2.2 and 3.8 and are possibly amorphous aluminite or basaluminite, respectively. They seem to have been formed in microenvironments enriched in sulphate, but also in fluoride anions. Their formation seems to have been enhanced by the combination of large inputs of acids and SO2 and an effective Al supply from weathering of volcanic glass.

Notes: Natural wetlands are a significant source of atmospheric methane, an important greenhouse gas. Compared with numerous papers on measurements of methane emission from natural wetland surfaces, there are few reports on methane configuration and distribution within wetland soil profiles. By using a newly designed gas sampler, we succeeded in collecting free-phase gas from beneath the water table down to 120 cm in a peat. The volumetric percentage of methane in the gas phase increased with depth and was generally more than 50% beneath the zone within which the water table fluctuates. The volume of the gas phase in the peat beneath the water table was estimated to be from 0 to 19% with significant variation with depth, suggesting uneven distribution of gas bubbles. Using the volume ratio of the gas and liquid phases and methane concentration data in the gas phase, as well as assuming that methane was in equilibrium (based on Henry's Law between the two phases), we calculated that ∼60% of the methane accumulates in the form of bubbles. These results suggest the importance of ebullition in methane emission, which might be a major cause for the reportedly large variation of methane emission in both space and time. Most importantly, our results show the need to consider gaseous-phase methane for understanding the production, transport and emission mechanisms of methane in wetlands, which has been overlooked to date.

Notes: Soil microbial biomass and microbial quotient (the ratio of soil microbial biomass to soil organic carbon) are considered to be useful as rapidly responding indicators of perturbations of soil properties. In this paper we will use a well-tested model (the continuous-quality theory) to analyse these variables in a Swedish 35-year-old field experiment with a black fallow, crop with no N addition, crop with calcium nitrate addition, and six treatments with organic amendments: straw, green manure, peat, farmyard manure, sawdust and sewage sludge.The model predicts correctly that the amount of microbial biomass increases for all the treatments with organic amendments compared with the black fallow treatment. The microbial biomass quotient increases also for all the amended treatments, except peat and sewage sludge, and decreases for the other treatments. The microbial biomass and microbial quotient increase with both the amounts of organic matter added (crop residues and amendments) and the quality of the added matter. However, to fully explain the observations it is also necessary to have an increasing microbial mortality with substrate quality. Moreover, short-term observations can be misleading with respect to both the magnitude and direction of long-term changes in biomass and related variables. Special attention must be paid to such amendments as sewage sludge, where contaminants such as heavy metals may determine process rates. We find no relation between microbial biomass or microbial quotient and yields.

Notes: The mobility of hydrophobic organic compounds (HOCs) in soils can be influenced by the presence of dissolved organic matter (DOM). While numerous studies have determined interactions of HOCs with humic and fulvic acids, only few data exist on the partitioning of HOCs to natural, non-fractionated DOM as it occurs in soil solutions. In this study, DOM was extracted from 17 soil samples with a broad range of chemical and physical properties, originating from different land uses. The partition coefficients of pyrene to DOM were determined in all soil extracts and for two commercial humic acids using the fluorescence quenching method. For the soil extracts, log KDOC values ranged from 3.2 to 4.5 litres kg−1. For the Aldrich and Fluka humic acids, log KDOC was 4.98 and 4.96 litres kg−1, respectively, thus indicating that they are not representative for soil DOM. After excluding these two values, the statistical analysis of the data showed a significant negative correlation between log KDOC and pH. This was also shown for one sample where the pH was adjusted to values ranging from 3 to 9. A multiple regression analysis suggested that ultraviolet absorbance at 280 nm (an indicator for aromaticity) and the E4:E6 ratio (an indicator for molecular weight) had additional effects on log KDOC. The results indicate that the partitioning of pyrene to DOM is reduced at alkaline pH, probably due to the increased polarity of the organic macromolecules resulting from the deprotonation of functional groups. Only within a narrow pH range was the KDOC of pyrene mainly related to the aromaticity of DOM.

Notes: This paper describes the characteristic shrinkage curve of a soil as it dries. It also introduces a new method to measure specific soil moisture states such as permanent wilting point and field capacity using the shrinkage curve. The model considers the soil fabric as a non-rigid, aggregated and unsaturated soil water medium. Its functional parameters (defined as pedohydral parameters) are the independent parameters of the shrinkage curve, which defines two major aspects of the structure of the fabric: (i) the volumetric functional elements of the soil fabric, and (ii) the arrangement of solid, water and air as functions of water content.Two African tropical soils were characterized and analysed according to a structural model with parameters of their shrinkage curve. The parameters of four soil horizons for the two soil types were determined continuously along their shrinkage curves. They were then used as descriptive variables representing the soil's hydrostructural behaviour in a canonical variate analysis, the results of which showed the A horizons to be distinct from the lower horizons, which appear as continua down the profiles. Analysis of the results reveals the importance of the clay and of the iron/clay ratio in the hydrostructural properties of the two soils. Transitional points of the shrinkage curve matched well some particular moisture states of the water potential curve, such as wilting points and field capacities. A more precise method of calculating water-holding characteristics and other structural properties such as air capacity and swelling index can be obtained from the characteristic shrinkage curve.

Notes: The organic matter (OM) of soils with andic properties has long been considered highly stable because of the presence of Al–humus complexes and sorption of organic ligands onto amorphous compounds. In this study, we characterized soils under different land use regimes located within an amphibolitic massif close to Santiago de Compostela (Spain), where soils with andic properties are present. Slash and burn agriculture was a common practice in the area until the second half of the 20th century. Thereafter, modern agriculture was progressively introduced into the area (AGR soils), and the rest of the land was either reforested or abandoned (FOR soils). We found that the mean organic C content of AGR soils (48.7 g kg−1) was ∼ 50% that of FOR soils (94.2 g kg−1). Mean soil pH was significantly greater (P 〈 0.05) in the AGR than in the FOR soils (4.95 compared with 4.63), which is attributed to liming and Ca-phosphate fertilization of the former. Mean concentrations of the Al forms studied (extractable with CuCl2, sodium pyrophosphate, ammonium oxalate, or NaOH) were significantly smaller (P 〈 0.01) in AGR (1.4, 4.9, 9.3, 11.0 g kg−1, respectively) than in FOR soils (3.9, 10.2, 16.5, 17.9 g kg−1, respectively). The results show the vulnerability of the OM and Al–humus complexes in these soils to modern agricultural practices, which has led to the attenuation – and in some cases even the disappearance – of andic soil properties in a relatively short time (〈 30 years) following changes in land use/management. We propose the inclusion of the formative element ‘andic’ in the criteria for the definition of Umbrisol subunits; this would avoid the abrupt discontinuity observed in the current World Reference Base classification.

Notes: A dairy system simulator, Dairy_sim, was designed to assess the interactions between climate and management in spring-calving milk production systems based on the grazing of grass pastures. The simulator comprises three main components: a grass herbage growth model, an intake and grazing behaviour model, and a nutrient demand model. The simulator was initially parameterized using the Irish National Dairy Blueprint. Sensitivity analysis indicated that the simulator was most sensitive to stocking rate, milk output per cow and nitrogen fertilizer inputs, but less sensitive to other variables. Field data from four grazing systems were used to test the simulator and it was concluded that Dairy_sim was suitable for evaluating the interaction of climate and management for rotational grazing dairy systems based on perennial ryegrass pastures with Friesian cows. The simulator, Dairy_sim, was then used to evaluate the effects of the regional climates of Ireland on system management. The results indicated that, between regions, herbage production at the same input of nitrogen may vary proportionally by 0·10 and that the length of the grazing season may vary by 0·25. It was concluded that the simulator could be a useful tool for developing region-specific dairy production blueprints.

Notes: Cycling of potassium in grassland systems has received relatively little attention in research and practice in recent years. Balanced nutrient systems require consideration of nutrients other than nitrogen (N). Potassium (K) is needed in large amounts and is closely related to N nutrition. In intensive dairy farming, surpluses of K arise from the input of concentrates and fertilizer and are returned to the grassland and may lead to increasing K content in the soil. Organic farming, on the other hand, is characterized by limitations in input of nutrient sources and quantities. Leaching of K from grassland is usually low, but high levels of available soil K, high K input from fertilizer or at urine patches lead to increasing losses. High K inputs have a negative influence on Mg and Ca uptake by plants and can cause accelerated leaching of these cations. High levels of K have been associated with inducing nutrition-related dairy cow health problems such as milk fever (hypocalcaemia) and grass tetany (hypomagnesaemia). This review gives an overview of the cycling of potassium and related cations in grassland systems especially with regard to leaching losses and identifies limitations to knowledge.

Notes: Advancing maize crop maturity is associated with changes in ear-to-stover ratio which may have consequences for the digestibility of the ensiled crop. The apparent digestibility and nitrogen retention of three diets (Early, Mid and Late) containing maize silages made from maize of advancing harvest date [dry matter (DM) contents of the maize silages were 273, 314 and 367 g kg−1 for the silages in the Early, Mid and Late diets respectively], together with a protein supplement offered in sufficient quantities to make the diets isonitrogenous, were measured in six Holstein–Friesian steers in an incomplete Latin square design with four periods. Dry-matter intake of maize silage tended to be least for the Early diet and greatest for the Medium diet (P = 0·182). Apparent digestibility of DM and organic matter did not differ between diets. Apparent digestibility of energy was lowest in the Late diet (P = 0·057) and the metabolizable energy concentrations of the three silages were calculated as 11·0, 11·1 and 10·6 MJ kg−1 DM for the Early, Medium and Late diets respectively (P = 0·068). No differences were detected between diets in starch digestibility but the number of undamaged grains present in the faeces of animals fed the Late diet was significantly higher than with the Early and Mid diets (P = 0·006). The apparent digestibility of neutral-detergent fibre of the diets reduced significantly as silage DM content increased (P = 0·012) with a similar trend for the apparent digestibility of acid-detergent fibre (P = 0·078). Apparent digestibility of nitrogen (N) was similar for the Early and Mid diets, both being greater than the Late diet (P = 0·035). Nitrogen retention did not differ between diets. It was concluded that delaying harvest until the DM content is above 300 g kg−1 can negatively affect the nutritive value of maize silage in the UK.

Notes: The effect of offering a total mixed ration of silage and concentrate (proportionately 0·44 silage) system [indoor feeding system (IF)] was compared with grazing at a high daily herbage allowance with a low level of concentrate supplementation [early grazing system (EG)] in early spring on the performance of spring-calving dairy cows in Ireland. Sixty-four spring-calving Holstein–Friesian dairy cows (mean calving date, 2 February) were allocated to one of two systems between 16 February and 4 April 2004. An equal number of primiparous and multiparous cows were assigned to each system. The dairy cows on the IF system were housed for a 7-week period and offered a diet of 10·9 kg DM cow−1 d−1 (s.d. 2·3) of concentrate, the remainder of the diet was 8·6 kg DM cow−1 d−1 (s.d. 1·9) of grass silage. The dairy cows on the EG system were offered a mean daily herbage allowance of 15·1 kg DM cow−1 d−1 (s.d. 3·7) and were supplemented with 3·0 kg DM cow−1 d−1 (s.d. 1·0) of concentrate. There was no difference in milk yield between the two systems but the cows in the EG system had a higher milk protein concentration (2·9 g kg−1) and a higher milk protein yield than in the IF system. Milk fat concentration was higher for cows in the IF than EG system (3·0 g kg−1). There was no difference in total daily dry-matter intake between the systems, measured in week 6 of the study. Mean live weight of the cows in the IF system was greater than in the EG system. The results of the study suggest that a slightly greater performance can be achieved by a system offering a high daily herbage allowance to spring-calving dairy cows in early lactation compared with a system offering a total mixed ration containing a high proportion of concentrate with grass silage.

Notes: The relative competitive ability of Artemisia frigida Willd. (C3, semi-shrub) and Cleistogenes squarrosa (Trin.) Keng (C4, perennial bunchgrass), grown in a greenhouse, was studied under three nitrogen fertilizer levels, three defoliation intensities and five competitive replacement series in a factorial arrangement. Relative yield total and the respective crowding coefficients for each species were calculated with reference to aboveground, below-ground and total biomass. The index of aggressivity was also determined relative to total biomass. Cleistogenes squarrosa was a consistently weak competitor at all nitrogen fertilizer and clipping levels compared with A. frigida. Artemesia frigida had a higher relative yield when grown in mixtures with C. squarrosa than in monocultures, whereas the yield of C. squarrosa was lower in mixtures with A. frigida than in monocultures. The relative competitive ability of A. frigida over C. squarrosa declined significantly at different clipping intensities with increasing nitrogen fertilizer. The interaction of nitrogen fertilizer with clipping was significant, although the clipping effect on aggressivity was not significant.

Notes: An experiment was conducted to determine the genetic variation among diploid perennial ryegrass (Lolium perenne L.) varieties for sward structural characteristics considered to be important for intake by cattle. Assessments were made between June and September in 2000 and 2001. Six varieties (Abergold, Respect, Agri, Herbie, Barezane and Barnhem) were subjected to a cutting experiment where swards were cut after 3 to 4 weeks of regrowth during the growing season. The variables, measured in three 2-week periods, were herbage mass of dry matter (DM), sward surface height (SSH), bulk density, proportion of green leaf, tiller density, tiller weight, extended tiller height, length of sheath and length of leaf blade. Significant differences among varieties were found in both years for herbage mass of DM, SSH, bulk density, proportion of green leaf, tiller density, tiller weight and length of sheath. The results show that there is significant genetic variation among diploid perennial ryegrass varieties for sward characteristics important for intake during grazing.

Notes: The effects of one severe winter-grazing of lucerne were studied over 3 years in an experiment in the Ebro Valley, Spain. In this region the crop is harvested six to seven times per season and winter grazing is a traditional practice. On average, winter-grazing reduced the yield at the first harvest in spring by 200 kg dry matter (DM) ha−1. This limited yield reduction of 0·06 was accompanied by an increase in the proportion of lucerne in the herbage DM from 0·54 to 0·62, a reduction in the proportion of weeds from 0·39 to 0·36, and a reduction in the proportion of dead material from 0·06 to 0·02. The crude protein concentration and the in vitro DM digestibility increased by 20 g kg−1 DM and 0·03, respectively. The traditional practice, i.e. of grazing lucerne with sheep once in the winter season, results in only a limited reduction in yield in the spring. In addition, the spring crop has a higher nutritive value.

Notes: Soil organic carbon (SOC) stocks in different terrestrial ecosystems have already been calculated. However, SOC stocks of grassy verges and grass-covered urban areas have never been reported. In this study the total grass-covered area of verges and urban areas in different agro-pedological regions of Flanders, Belgium was calculated and SOC stocks estimated. The total grassy area of verges along roads, waterways and railways was calculated to be 18 027 ha, 9530 ha for gardens and parks and 2360 ha for recreations areas. Total SOC stock for grass-covered verges, extrapolated to a depth of 1 m, was estimated to be 3520 kt SOC. Total SOC stock for grassy vegetation in urban areas was 1738 kt SOC. These total SOC stocks equate, respectively, to 0·10 and 0·05 of the total SOC stock in Flemish grassland.

Notes: The survival of pathogenic and spoilage micro-organisms in soil and on grass fertilized with spiked anaerobic digestion residue (ADR) was investigated in a climate chamber during periods of up to 56 d. In addition, the survival of these organisms over time was investigated during ensiling of grass at 390 g dry matter (DM) kg−1 or 610 g DM kg−1. Micro-organisms included in these studies were: Clostridium tyrobutyricum, Salmonella serotype Typhimurium, Listeria monocytogenes, Campylobacter jejuni, Escherichia coli, Talaromyces emersonii, Byssochlamys nivea, Porcine parvovirus and Swine vesicular disease virus. Soil and grass still contained high numbers of E. coli, Cl. tyrobutyricum and T. emersonii (1·9–5·4 log10) 49 and 56 d after fertilization with spiked ADR. Listeria monocytogenes and S. Typhimurium were generally found in the samples. This indicates that, within this time span, there is a risk of silage contamination by bacteria, moulds and viruses present in ADR spread on grassland. An increase in DM content of the crop decreased its ensilability as measured by pH and short-chain fatty acid content. However, no clear differences were found in survival of pathogenic and spoilage micro-organisms between the two silages with different DM contents, regardless of storage time. The lack of moisture and oxygen was probably sufficient to cause the reduction in vegetative bacteria in the 610 g DM kg−1 silage. However, bacterial and fungal spores and the viruses studied were not significantly inactivated by ensiling at these high DM contents and could, therefore, pose a health risk to farm animals fed on the silage if present in ADR applied to crops prior to ensilage.

Notes: Cattle and sheep can create and maintain a mixture of relatively tall and short patches in grass swards through selective grazing. In swards that are grazed by cattle this heterogeneous structure can result in the frequencies of height measurements having a skewed distribution that has variously been better described by the double-normal distribution the gamma distribution and the Weibull distribution than by the more common normal distribution. The fit of these statistical distributions, and the adequacy of the potentially useful log-normal distribution, to sward height frequencies were tested in sown temperate swards grazed by sheep and compared within a single sward. It was concluded that the single-normal and Weibull distributions were inadequate and that overall the log-normal and gamma distributions had the best fit to the measurements.

Notes: Descriptions of anthropocentric phenologies of flower colour were obtained for all thirteen British mesotrophic grassland communities, defined by the National Vegetation Classification. They were obtained by combining information on species abundance with data on flowering time and flower colour. Although the results are crude estimates, they clearly demonstrate that grassland communities differ in their floral phenologies with yellow-flowered species being significantly most abundant, and blue-flowered species being least abundant than the colours of other flowering species in British grasslands. The peak months for flowering were June and July. Significant interactions were observed between community type and flower colour; community type and month; and flower colour and month. These interactions may be explained by ecological differences between the communities, for example hay meadows flowered earlier than other grassland types. It is argued that other differences between communities in their floral phenologies, for example the absence of blue flowers from the agriculturally improved MG7 and MG11 swards, may support the hypothesis that the limited availability of pollination niches may affect plant community structure.

Notes: The contention that agricultural grassland within the UK is spatially and structurally uniform across wide differences in livestock farming intensity is examined. Total nitrogen (N) input was used as a surrogate for management intensity. Farms with average annual N inputs of 〉200 kg ha−1 were categorized as highly intensive, those with N inputs of 50–200 kg N ha−1 as moderately intensive and those with inputs of 〈50 kg N ha−1 were categorized as extensive. Four farms within each management category were selected in two discrete regions: one in south-west England, typifying a landscape dominated by agricultural grassland, the other in south-east England with a more mixed-farming landscape. Specific N input and management data, and sward botanical composition and structure, were obtained on four fields per farm. The south-west region had a higher proportion of farms with dairy cattle than in the south-east England region. The average N input and stocking rates were higher within the intensive-management category farms in south-west England than in south-east England. Old permanent grasslands contained variable amounts of sown species, such as Lolium perenne, and were dominated by a few (generally 〈5) non-sown grass species. Grassland that received 〉75 kg N ha −1 year−1 contained 〈7 plant species and 〈3 forb species m−2. Grassland communities with 〉12 plant species and 〉5 forb species m−2 were only found in study fields that received 〈50 kg N ha−1 year−1. Grasslands with 〉10 forb species m−2 were found only in sites receiving 〈15 kg N ha−1. Of importance at a landscape scale was ubiquity of species-poor and similar grassland plant communities across the management intensity range within and between livestock farms. Grassland in the extensive management category was similar in structure in terms of sward height and/or sward density to more intensively managed grasslands. This study revealed, albeit in two lowland sample regions in the UK, the ubiquity of grass-dominated, species-poor and structurally uniform grasslands, irrespective of apparently broad differences in farming intensity. The consequences of this spatial uniformity on grassland biodiversity are likely to be profound.

Notes: The effects of offering a range of grass silages and mixtures of grass and maize silages on the intake of beef cattle were studied. Four grass silages (GS1, GS2, GS3 and GS4) were used. Grass silage 1 was ensiled from a second regrowth in mid-late September and treated with an inoculant additive. Grass silages 2, 3 and 4 were ensiled, without additive, from a primary regrowth harvested in early July, late May and mid-June respectively. Wilting periods were 8, 30, 36 and 36 h for GS1, GS2, GS3 and GS4 respectively. Grass silages 1, 2 and 3 were precision chopped and ensiled in bunker silos, while GS4 was ensiled in round bales. The DM content (g kg−1) and starch concentration (g kg−1 DM) of the three maize silages (MS1, MS2 and MS3) used were 256 and 128, 256 and 184, and 402 and 328 for MS1, MS2 and MS3 respectively. Seventy-two Charolais and Limousin cross-bred steers were used in a changeover design with two 4-week periods. The study consisted of sixteen treatments incorporating the four grass silages fed alone and with the three maize silages arranged as a 4 × 4 factorial design. The grass silage and maize silage mixtures were offered in a ratio of 0·60:0·40 (DM basis) once daily using individual Calan gates. All silages were offered ad libitum with 3 kg per head per day of a concentrate supplement. Dry matter and metabolizable energy (ME) intakes were highest with diets based on grass silage GS4 compared with diets containing the other grass silages. Metabolizable energy intakes of diets containing no maize silage, and those based on MS1 and MS2, were similar (P 〉 0·05) but lower than that of diets containing MS3. Only limited increases were found in DM and ME intakes with the inclusion of maize silage in grass silage-based diets while offering high-quality grass silage (assessed in terms of DM content, and fibre and N concentrations) promoted high voluntary intakes.

Notes: We know much about the influence of management on stocks of organic matter in subtropical soils, yet little about the influence on the chemical composition. We therefore studied by CPMAS 13C NMR spectroscopy the composition of the above-ground plant tissue, of the organic matter of the whole soil and of silt- and clay-size fractions of the topsoil and subsoil of a subtropical Acrisol under grass and arable crops. Soil samples were collected from three no-till cropping systems (bare soil; oats−maize; pigeon pea + maize), each receiving 0 and 180 kg N ha−1 year−1, in a long-term field experiment. Soil under the original native grass was also sampled. The kind of arable crops and grass affected the composition of the particulate organic matter. There were no differences in the composition of the organic matter in silt- and clay-size fractions, or of the whole soil, among the arable systems. Changes were observed between land use: the soil of the grassland had larger alkyl and smaller aromatic C contents than did the arable soil. The small size fractions contain microbial products, and we think that the compositional difference in silt- and clay-size fractions between grassland and the arable land was induced by changes in the soil's microbial community and therefore in the quality of its biochemical products. The application of N did not affect the composition of the above-ground plant tissue nor of the particulate organic matter and silt-size fractions, but it did increase the alkyl C content in the clay-size fraction. In the subsoil, the silt-size fraction of all treatments contained large contents of aromatic C. Microscopic investigation confirmed that this derived from particles of charred material. The composition of organic matter in this soil is affected by land use, but not by variations in the arable crops grown.

Notes: Oxidative treatment can isolate a stable organic matter pool in soils for process studies of organic matter stabilization. Wet oxidation methods using hydrogen peroxide are widely used for that purpose, but are said to modify poorly crystalline soil constituents. We investigated the effect of a modified NaOCl oxidation (pH 8) on the mineral composition of 12 subsoils (4.9–38.2 g organic C kg−1) containing varying amounts of poorly crystalline mineral phases, i.e. 1.1–20.5 g oxalate-extractable Fe kg−1, and of different phyllosilicate mineralogy. Post-oxidative changes in mineral composition were estimated by (i) the determination of elements released into the NaOCl solution, (ii) the difference in dithionite- and oxalate-extractable Si, Al and Fe, and (iii) the specific surface areas (SSAs) of the soils. The NaOCl procedure reduced the organic C concentrations by 12–72%. The amounts of elements released into the NaOCl extracts were small (≤ 0.14 g kg−1 for Si, ≤ 0.13 g kg−1 for Al, and ≤ 0.03 g kg−1 for Fe). The SSA data and the amounts of dithionite- and oxalate-extractable elements suggest that the NaOCl oxidation at pH 8 does not attack pedogenic oxides and hydroxides and only slightly dissolves Al from the poorly crystalline minerals. Therefore, we recommend NaOCl oxidation at pH 8 for the purpose of isolating a stable organic matter pool in soils for process studies of organic matter stabilization.

Notes: A well-developed podzol hydrosequence that has been partially covered with drift sand, and partially subjected to improved drainage, provides new insights into the causes of variation in soil organic matter chemistry in such soils. While E horizons invariably move towards a dominance of aliphatic components reflecting residual accumulation, the chemistry of organic matter in well-drained B horizons is determined mainly by decaying roots, which are transformed by microorganisms to humus aggregates. In poorly drained, stratified B horizons, humus coatings dominate and the chemistry is very close to that of dissolved organic carbon. When a sand cover inhibits the supply of fresh litter, microbial decomposition in the A horizon causes a shift in chemistry towards that of the E horizon. Similarly, upon improved drainage and removal of complexed metals from the top of the B horizon, microbial decomposition of all palatable organic matter in the top of the B horizon causes a shift towards E-horizon chemistry. This is probably the mechanism by which most E horizons in podzols are formed, and not by re-solution. Marked chemical changes upon improved drainage may take only decades. During microbial decay, small polysaccharide-derived pyrolysis products (mainly furans, furaldehydes and acetic acid) remain abundant due to the contribution of microbial sugars. Both micromorphology and factor analysis on quantified results of pyrolysis-gas chromatography/mass spectrometry contribute significantly to the interpretation of the humus chemistry of these profiles and thus to our understanding of soil genesis. Organic chemistry of the investigated podzols can be understood only in the context of their genesis.

Notes: Water repellency can be a significant factor in soil physical behaviour, but little is known about the depth dependence of the contact angle of field soils. We investigated contact angles and wetting properties as a function of depth for a wide range of agricultural and forest soils in Germany. The agricultural soils ranged from silty to sandy texture (six profiles), and the forest soils ranged from sandy to loamy texture (eight profiles). Contact angles (CA) were measured with the Wilhelmy plate method (WPM). In most of the soils, advancing WPM contact angles were considerably greater than 0°  and they varied irregularly with depth. In general, sandy soils had larger WPM contact angles than silty soils. From the relation of the contact angle with texture and pH the quality of soil organic matter (SOM) was considered as more important for the wetting properties than the total amount of soil organic carbon (SOC). Finally, it was found that for soils with intermediate sand contents either under agricultural or forest use, the kind of land use seemed not to influence CA. Coarse-textured sandy soils that were used only as forest sites were more hydrophobic than silty soils which were exclusively used as agricultural soils. We conclude that a coarse texture favours, in combination with other factors (mainly pH), hydrophobic SOM.

Notes: Aggregate breakdown due to rainfall action causes crusting and interrill erosion. Erodibility is seemingly determined by the capacity of surface aggregates to resist the effects of rainfall. In this paper, we evaluated the relevance of an aggregate stability measurement, which comprises three treatments, in order to characterize aggregate breakdown dynamics. Two cultivated soils were studied: a clay loam slightly sensitive to erosion and a more susceptible silt loam. We compared the size distributions of microaggregates produced by the three aggregate stability treatments with the results from a rainfall simulation. The behaviour of four initial aggregate size classes (〈 3 mm, 3–5 mm, 5–10 mm and 10–20 mm) was also compared to study the influence of the initial aggregate size on the nature of resulting aggregates. The mean weight diameter was from 200 to 1400 µm for the silt loam and from 600 to 7000 µm for the clay loam. The two experiments – aggregate stability measurements and aggregate breakdown dynamics under rainfall – yielded similar results. Qualitative analysis showed that for both soils the sizes of fragments produced by breakdown with the aggregate stability tests and under rainfall were similar and seemed to be qualitatively independent of the size of initial aggregates. We first schematized the structural organization of aggregates in cultivated horizons with a simple hierarchical model at two levels: (i) 〈 250 µm microaggregates and (ii) 〉 250 µm macroaggregates made by the binding together of microaggregates. We then developed a model of aggregate breakdown dynamics under rainfall which gives, for various rainfall durations, the size distributions of resulting fragments on the basis of aggregate stability measurements. We obtained a correlation coefficient, r, of 0.87 for the silt loam and of 0.91 for the clay loam, showing that the experimental and predicted mass percentages were linearly related for each size fraction.

Notes: The use of ultrasonic energy for the dispersion of aggregates in studies of soil organic matter (SOM) fractionation entails a risk of redistribution of particulate organic matter (POM) to smaller particle-size fractions. As the mechanical strength of straw also decreases with increasing state of decomposition, it can be expected that not all POM will be redistributed to the same extent during such dispersion. Therefore, we studied the redistribution of POM during ultrasonic dispersion and fractionation as a function of (i) dispersion energy applied and (ii) its state of decomposition. Three soils were dispersed at different ultrasonic energies (750, 1500 and 2250 J g−1 soil) or with sodium carbonate and were fractionated by particle size. Fraction yields were compared with those obtained with a standard particle-size analysis. Undecomposed or incubated (for 2, 4 or 6 months) 13C-enriched wheat straw was added to the POM fraction (0.25–2 mm) of one of the soils before dispersion and fractionation. Dispersion with sodium carbonate resulted in the weakest dispersion and affected the chemical properties of the fractions obtained through its high pH and the introduction of carbonate. The mildest ultrasonic dispersion treatment (750 J g−1) did not result in adequate soil dispersion as too much clay was still recovered in the larger fractions. Ultrasonic dispersion at 1500 J g−1 soil obtained a nearly complete dispersion down to the clay level (0.002 mm), and it did not have a significant effect on the total amount of carbon and nitrogen in the POM fractions. The 2250 J g−1 treatment was too destructive for the POM fractions since it redistributed up to 31 and 37%, respectively, of the total amount of carbon and nitrogen in these POM fractions to smaller particle-size fractions. The amount of 13C-enriched wheat straw that was redistributed to smaller particle-size fractions during ultrasonic dispersion at 1500 J g−1 increased with increasing incubation time of this straw. Straw particles incubated for 6 months were completely transferred to smaller particle-size fractions. Therefore, ultrasonic dispersion resulted in fractionation of POM, leaving only the less decomposed particles in this fraction. The amounts of carbon and nitrogen transferred to the silt and clay fractions were, however, negligible compared with the total amounts of carbon and nitrogen in these fractions. It is concluded that ultrasonic dispersion seriously affects the amount and properties of POM fractions. However, it is still considered as an acceptable and appropriate method for the isolation and study of SOM associated with silt and clay fractions.

Notes: Soils are increasingly viewed as a potential sink for atmospheric carbon. However, their use to meet CO2 emission reductions is problematic for there are knowledge gaps regarding the mechanisms involved in the sequestration of organic carbon (OC). There is evidence which suggests that OC concentrations are controlled by the mineralogy and related specific surface area (SSA) of a given soil. The goal of this study was to examine the importance of sorptive mechanisms on OC stabilization. The objectives were (i) to determine the SSA, clay mineralogy and dithionite- and oxalate-extractable Fe and Al concentrations of several soils, and (ii) to analyse how these variables are related to OC concentrations. Five soils were sampled and analysed: two Umbrisols, a Stagnic Acrisol, an Anthrosol/Vertisol/Gleysol-Chernozem and a Gleysol (FAO terminology), all located in Hesse, Germany. Oxalate-extractable Fe and Al were found to be the best predictors of OC concentrations in the soils examined. Specific surface area correlated significantly with the OC content of the B and C horizons of one Umbrisol and the entire profile of the Anthrosol/Vertisol/Gleysol-Chernozem. The relationship between SSA and OC concentrations is likely to be restricted to certain soils and might be a product of the sorptive capacity of Fe and Al oxides. We can assume that the available mineral surface area on oxides is a limiting factor in terms of a soil's capacity to sequester organic carbon. As such, attention should be paid to soil mineralogy and how this might limit the use of soils as a sink for atmospheric CO2.

Notes: In the Ecuadorian Cordillera, the hardened volcanic ashes (cangahuas) account for 15% of the cultivated area. The soil resulting from the fragmentation of these materials, generally by heavy machinery, shows an apparent stable millimetric structure. However, this new structure is highly susceptible to disintegration under rain, because it contains no organic matter and little clay, and the material itself is readily eroded in consequence.We studied the evolution of soil aggregate stability in two factorial experiments during five cultivation cycles with two kinds of soil preparation and five fertilization treatments. The aggregate stability was not influenced by either kind of soil preparation, nor by large additions of cattle manure (80 t ha−1) or green manure (10 t ha−1), nor by growing a perennial grass. The variation in the aggregate stability seemed to depend on the components inherited from the original volcanic material: in the plots with larger clay content, and with swelling clay minerals, the aggregates were less stable than those composed of isometric fine silt particles.

Notes: The water retention characteristic provides the traditional data set for the derivation of a soil's pore-size distribution. However, the technique employed to achieve this requires that assumptions be made about the way pores interconnect. We explore an alternative approach based on stray field nuclear magnetic resonance (STRAFI-NMR) to probe the water-filled pores of both saturated and unsaturated soils, which does not require information relating to pore connectivity. We report the relative size distributions of water-occupied pores in saturated and unsaturated samples of two sets of glass beads of known particle size, two sands, and three soils (a silty loam, a sandy loam and a loamy sand), using measurements of the NMR T1 proton relaxation time of water. The T1 values are linearly related to pore size and consequently measured T1 distributions provide a measure of the pore-size distribution. For both the sands and the glass beads at saturation the T1 distributions are unimodal, and the samples with small particle sizes show a shift to small T1 values indicating smaller voids relative to the samples with larger particles. Different matric potentials were used to reveal how the water-occupied pore-size distribution changes during drainage. These changes are inconsistent with, and demonstrate the inadequacies of, the commonly employed parallel-capillary tube model of a soil pore space. We find that not all pores of the same size drain at the same matric potential. Further, we observe that the T1 distribution is shifted to smaller values beyond the distribution at saturation. This shift is explained by a change in the weighted average of the relaxation rates as the proportion of water in the centre of water-filled pores decreases. This is evidence for the presence of pendular structures resulting from incomplete drainage of pores. For the soils the results are similar except that at saturation the T1 distributions are bimodal or asymmetrical, indicative of inter-aggregate and intra-aggregate pore spaces. We conclude that the NMR method provides a characterization of the water-filled pore space which complements that derived from the water retention characteristic and which can provide insight into the way pore connectivity impacts on drainage.

Notes: Soil response to acid and sulphur inputs is influenced largely by the soil's physico-chemical properties. We studied the effects of such depositions in two types of Andosols exposed to volcanogenic emission (Masaya, Nicaragua), namely Eutric Andosols rich in allophanic constituents, and Vitric Andosols rich in volcanic glass. Small mineral reserves and large contents of secondary short-range ordered minerals indicate a more advanced weathering of the Eutric than the Vitric Andosols. Strong correlations between soil specific surface and oxalate-extractable Al, Si and Fe contents highlight the predominant contribution of short-range ordered minerals to surface area.Both types of Andosols showed a decrease in pH upon acid input. Sulphur deposition increased the soil's S content to 5470 mg S kg−1. However, the acid neutralizing capacity of the soil solid phase (ANCs) was not significantly affected by the acid and S inputs. Non-exchangeable (mineral reserve) and exchangeable cations and total contents of sulphur and phosphorus dictate most of the ANCs variation. In the Vitric Andosols, mineral reserves contributed up to 97% to these four additive pools, whereas the exchangeable cations accounted for 1–4%. In the Eutric Andosols, the contribution of mineral reserves was less (71–92%), but the exchangeable cation content was greater (1–20%), whereas the contribution of sulphur and phosphorus was significant at 1–15% and 2–7%, respectively. The main process involved in H+ consumption is mineral weathering in Vitric Andosols and ion exchange in Eutric Andosols.

Notes: Sulphate sorption on to the surface of short-range ordered minerals and precipitation of Al-hydroxy sulphate contribute to the acid neutralizing capacity of soils. The correct measurement of total inorganic sulphate is thus essential in soils that are accumulating SO42– anions. We extracted SO42– by various solutions, namely 0.005 m Ca(NO3)2, 0.016 m KH2PO4, 0.5 m NH4F and 0.2 m acidic NH4-oxalate (pH 3), from Vitric and Eutric Andosols exposed to prolonged deposition of acid and SO2 from an active volcano (Masaya, Nicaragua). We attributed sulphate extractable by KH2PO4 (20–3030 mg kg−1) to anion-exchangeable SO42–, which was much smaller than NH4F- and oxalate-extractable SO42– (400–9680 and 410–10 480 mg kg−1, respectively). Our results suggest the occurrence of a sparingly soluble Al-hydroxy-mineral phase extractable by both NH4F and oxalate. The formation of Al-hydroxy minerals would result from the combination of enhanced weathering caused by strong acid loading and simultaneous occurrence of large SO42– concentrations in soil solution. Oxalate extracted slightly more inorganic SO42– than did NH4F, this additional amount of SO42– correlating strongly with oxalate-extractable Si and Fe contents. Preferential occlusion of SO42– by short-range ordered minerals, especially ferrihydrite, explains this behaviour. If we exclude the contribution of occluded sulphate then oxalate and NH4F mobilize similar amounts of SO42– and are believed to mobilize all of the inorganic SO42– pool.

Notes: Topsoil samples from cultivated and adjacent non-cultivated fields on three major agricultural soils in North Cameroon were fractionated into particle-size fractions that were analysed subsequently for their C and 13C contents. The aim was to obtain further insight into the dynamics of soil organic matter (SOM) in relation to land use in Cameroon. Since organic carbon contents of the fractions were often very small, samples and analyses were extensively replicated to obtain robust statistical estimates of observed differences. For each soil type, differences in δ13C values between fields could be related to changes in the input and decomposition of organic matter arising from soil type, land management and, for example, the nature and abundance of weeds. Turnover of organic matter appeared to be fastest in the sand fraction, which is in line with results from earlier studies. In the finer fractions, clear differences in reaction to changes in input and decomposition were observed, that seem to be linked to differences in clay mineralogy. The results illustrate that SOM in the various fractions is much less stable and more strongly affected by changes in land use than might be assumed on the basis of changes in total SOM contents alone. At the same time, they demonstrate the relevance of 13C isotope analyses of SOM for studies on the impact of land use on these savannah soils with little SOM that are highly susceptible to degradation.

Notes: The effects of past applications of farmyard manure (FYM, applied from 1942 to 1967), metal-contaminated sewage sludge (applied from 1942 to 1961) and mineral fertilizer (NPK, applied from 1942 until now) on the microbial biomass and community structure in a sandy loam, arable soil from the Woburn Market Garden Experiment, UK, were investigated in 1998. Concentrations of Cu, Ni and Zn in soils which previously received sewage sludge were less than current European Union (EU) limits, but the soil Cd concentration was more than twice the permitted limit. Organic-C concentration in the FYM-treated soil and contaminated soils was about twice that of NPK-treated soil. The initial microbial biomass-C and estimates of total bacterial numbers by acridine orange direct count were significantly (P 〈 0.05) greater in the FYM-treated soil compared with the NPK-treated and the most contaminated soils. Total phospholipid fatty acid (PLFA) concentration (another measure of biomass) was significantly greater in the FYM-treated soil compared with either the low or high metal-contaminated soils, both of which contained similar PLFA concentrations. In the metal-contaminated soils, in contrast, fluorescent Pseudomonas counts, as a percentage of total plate counts, were at least 1.5 times greater than in the uncontaminated soils. The concentrations of these microbial parameters were significantly (P 〈 0.05) less in the NPK soil than in all the other treatments. Biomass-C as a percentage of organic-C was also significantly (P 〈 0.05) greater in the uncontaminated soils compared with the metal-contaminated soils. Biomass specific respiration rates in the metal-contaminated soils were c. 1.5 times those in the FYM-treated soil. In the metal-contaminated soils, the concentration of mono-unsaturated and hydroxy-fatty acids (derived from phospholipids), and lipopolysaccharide hydroxy-fatty acids (all indicative of Gram-negative bacteria) were significantly (P 〈 0.05) greater than branched fatty acids (indicative of Gram-positive bacteria). Furthermore, Gram-negative counts were 62–68% greater than Gram-positive counts in the metal-contaminated soils. Branched fatty acid concentration was significantly (P 〈 0.05) greater in the FYM-treated soil than in the metal-contaminated soils. Gram-positive counts were also 63% greater than Gram-negative counts in the FYM-treated soil. We found that effects of the relatively small heavy metal concentration caused measurable decreases in soil microbial biomass-C concentrations, acridine orange direct counts and Gram-positive counts. There were also increases in biomass specific respiration rates, and the microbial community had changed substantially, nearly 40 years after the metal inputs ceased. We conclude that, at the very least, the current EU permitted limits for heavy metals in agricultural soils should not be relaxed.

Notes: We used the wavelet transform to quantify the performance of models that predict the rate of emission of nitrous oxide (N2O) from soil. Emissions of N2O and other soil variables that influence emissions were measured on soil cores collected at 256 locations across arable land in Bedfordshire, England. Rate-limiting models of N2O emissions were constructed and fitted to the data by functional analysis. These models were then evaluated by wavelet variance and wavelet correlations, estimated from coefficients of the adapted maximal overlap discrete wavelet transform (AMODWT), of the fitted and measured emission rates.We estimated wavelet variances to assess whether the partition of the variance of modelled rates of N2O emission between scales reflected that of the data. Where the relative distribution of variance in the model is more skewed to coarser scales than is the case for the observation, for example, this indicates that the model predictions are too smooth spatially, and fail adequately to represent some of the variation at finer scales. Scale-dependent wavelet correlations between model and data were used to quantify the model performance at each scale, and in several cases to determine the scale at which the model description of the data broke down. We detected significant changes in correlation between modelled and predicted emissions at each spatial scale, showing that, at some scales, model performance was not uniform in space. This suggested that the influence of a soil variable on N2O emissions, important in one region but not in another, had been omitted from the model or modelled poorly. Change points usually occurred at field boundaries or where soil textural class changed.We show that wavelet analysis can be used to quantify aspects of model performance that other methods cannot. By evaluating model behaviour at several scales and positions wavelet analysis helps us to determine whether a model is suitable for a particular purpose.

Notes: Crack development is predominant in soil structure formation. A number of fracture mechanics models have been applied to soil to describe cracking, but most are not applicable for soil in a wet, plastic state. We address this weakness by applying a new elastic–plastic fracture mechanics approach to describe crack formation in plastic soil. Samples are fractured using a deep-notch (modified four-point) bend test, with data on load transmission, sample bending, crack growth, and crack-mouth opening collected to assess the crack-tip opening angle (CTOA). CTOA provides a powerful parameter for describing soil cracking since it can be induced by soil shrinkage (an easily measured parameter) and can be used to describe elastic–plastic fracture in numerical approximations, such as finite element modelling. The test variables we studied were the direction of the applied consolidation stress, clay content, and pore water salinity. All samples were formed by consolidating soil slurry one-dimensionally with a 120-kPa vertical effective stress. Tests on pure kaolinite showed that the direction of the consolidation stress did not affect CTOA, which was 0.23 ± 0.02 m m−1 for specimens cut both in a horizontal and in a vertical direction to the applied stress. Soil clay content had a marked influence, however, with silica sand:kaolinite mixtures by weight of 20:80 and 40:60 reducing CTOA to 0.14 ± 0.02 m m−1 and 0.12 ± 0.01 m m−1, respectively. These smaller values of CTOA indicate that less strain is required to induce fracture when the amount of clay is less. Salinity (0.5 m NaCl) caused a reduction in the CTOA of pure kaolinite from 0.23 ± 0.02 m m−1 to 0.17 ± 0.03 m m−1.

Notes: The fermentation quality of small-bale silage and haylage for feeding to horses in Sweden, and using a conventional high-density hay baler, was investigated in two experiments. Treatments studied were use of additives (inoculants containing lactic acid bacteria and a chemical additive consisting of hexamethylenetetramine, sodium nitrate, sodium benzoate and sodium propionate), the influence of dry-matter (DM) content of wilted herbage and the effect of number of stretch film layers on fermentation pattern and aerobic stability. All silages and haylages were made from predominantly Timothy swards and were well fermented as indicated by low levels of ammonia and butyric acid. Values of pH were higher and concentrations of organic acids were lower in haylages than in the silages. This was not considered to be indicative of a poor fermentation in the haylage but of a restricted fermentation due to the high DM content of the herbage. The additives enhanced aerobic storage stability because of inhibition of mould growth. The only statistically significant effect of varying the number of stretch film layers was a higher content of CO2 inside the bales when ten layers of stretch film were applied compared with six layers.

Notes: Factors reducing yield of organic white clover seed production were investigated in Denmark. In thirty-six fields from different regions, density of flower heads, and weevils of the genera Apion and Hypera, hatching from flower heads, were assessed. In fifteen of these fields, additional measurements were made in order to calculate potential yield and yield-reducing factors. Flower heads had a mean of ninety-two florets per head, of which proportionately 0·59 were intact, 0·08 were not pollinated and 0·34 damaged by weevils; 0·16 of the florets contained larvae of Apion species. In intact florets the mean number of seeds was 3·6. Density and size of flower heads were correlated with low density of flower heads leading to significantly more florets per head. The number of seeds per intact floret was correlated with the proportion of unpollinated florets. The number of insect-damaged florets was influenced by both larvae of Apion in and the numbers of Hypera nigrirostris (Fabr.) hatched from flower heads. One larva of H. nigrirostris caused approximately ten times the damage of a larva of Apion. Densities of Apion and Hypera were influenced by location, with fields with adjacent weevil sources being most at risk. An estimate of potential seed yield showed that, even under good harvest conditions, only a small part of potential seed yield is realized and that under suboptimal harvest conditions seed loss is high. The main factors responsible for low yields in Danish organic white clover seed production were identified as unfavourable harvest conditions and weevil damage.

Notes: Demographic and biomass allocation patterns of Agropyron cristatum were measured on steppe and dune sites in the Hunshandake desert of North China in 2001 and 2002. Total plant population, reproductive shoot densities and its differentiation rates were significantly higher in the steppe sites in both years. Plant heights for both vegetative and reproductive shoots were greater in the year with the higher rainfall. The dune sites had a higher biomass allocation to vegetative shoots and roots, while the steppe sites had a higher biomass allocation to reproductive shoots and seed production. It is suggested that the population demography and biomass allocation of the species responded to the differences in the soil variables in the steppe and dune sites.

Notes: The objective was to determine how the frequency and intensity of defoliation of tall oat grass [Arrhenatherum elatius (L.) Presl.], affected (i) annual dry-matter (DM) accumulation, (ii) seasonal distribution of the accumulated forage, and (iii) morphological traits related to persistence and vigour. Data were collected twice a year throughout three growing years, beginning the second year after establishment. Two frequencies (A: each time modal height of plants reached 20 cm; B: each time modal height of plants reached 40 cm) and two defoliation intensities (I: 5 cm; II: 10 cm stubble) were arranged in a completely randomized block design with a fully factorial combination and four replicates. Measurements were made of annual DM accumulation, seasonal distribution of accumulated DM and morphological traits related to persistence and vigour, i.e. number of tillers m−2, number of tussocks m−2, crown diameter, and crown area of tussocks. The infrequent defoliation (B) increased annual DM accumulation besides maintaining levels of persistence and vigour. The most productive treatment (BI) had a significantly higher annual DM accumulation than treatments AI and AII. Frequent and severe defoliations (treatment AI) led to plant depletion, which reduced crown diameter, number of tillers m−2 and crown area at the end of the third year compared with infrequent but severe defoliation (treatment BI). Annual DM accumulation was intermediate for less intense defoliations (AII), which produced forage during winter, but resulted in less vigorous plants by the end of the experiment. Crown area was a good indicator of tiller number, particularly under frequent defoliation.

Notes: Field survey and satellite image processing methods were used to estimate the total available forage over an area of 95 034 ha in north-eastern Syria, and to assess grazing impact on the area. The above-ground plant biomass was measured by a quadrat method at three sites in each of eight vegetation classes. Available forage was measured by excluding woody parts of shrubs from the whole aerial plant parts. The total above-ground plant biomass and available forage were estimated by extrapolating the measured point data to the whole target area using classified vegetation data by satellite image processing. Grazing impact was assessed by calculating the differences between the total available forage at the end of growing season and the end of dry season. The values for the estimated total available forage (s.e. of mean) in the area were 55 628 000 (12 920 000) kg DM and 30 007 000 (2 437 000) kg DM at the end of growing season and dry season respectively. Although the area of the cereal fields covered only 0·315 of the area, about 0·69 and 0·82 of the available forage existed in the harvested cereal fields at the ends of growing season and dry season respectively. The integration of cereal fields and rangeland is a normal land use system for livestock management in the area. The higher cover of herbaceous vegetation types showed higher grazing impacts which reduced the total available forage at the end of the growing season by 0·817 (0·199) at the end of the dry season. Although these dense herbaceous vegetation types could possibly produce more available forage, they would incur more intensive grazing impact. On the contrary, lighter grazing impact would occur with a higher cover of shrub vegetation types. The importance of maintaining plant cover over the rangeland area to protect the land against soil erosion is stressed.

Notes: Introgression of reproductive traits from the annual, profuse flowering, ball clover (Trifolium nigrescens Viv.) into white clover (Trifolium repens L.) is one breeding strategy to improve seed yields of T. repens that must be achieved without sacrificing agronomic performance and persistency under grazing. The yield and persistency of hybrids between white clover and T. nigrescens were compared under rotational sheep grazing over three harvest years. The hybrids included the backcross (BC) 2 and 3 generations produced using white clover as the recurrent parent. The large-leaved T. repens variety Olwen, medium-leaved varieties AberDai and Menna and the small-leaved variety S184 were sown as controls. Hybrids and control varieties were sown with a perennial ryegrass companion; between April and the end of October in each harvest year the plots were rotationally grazed with sheep with clover and perennial ryegrass (DM) yield and the proportion of clover present measured over the growing season. The clover and total DM yields of the BC2 and BC3 were generally comparable with the small- and medium-leaved varieties within the experiment and significantly greater than the yields of the large-leaved variety Olwen. Throughout the 3 years of the experiment the BC2 maintained a clover content above 0·30 and comparable with the small-leaved varieties, while the clover content of the BC3 was comparable with the small- and medium-leaved varieties in the first and third harvest years. No significant difference in perennial ryegrass production was observed when grown with the backcrosses or the control varieties. Differences in stolon and growing-point density were observed at the end of the experiment with the density of the BC2 and BC3 less than the small-leaved variety S184 but, in common with the medium-leaved varieties, greater than the large-leaved variety Olwen. The implication of these results for the use of this material in future experiments and in the white clover breeding programme is discussed.

Notes: Three experiments were conducted to determine the association between leaf number per tiller at defoliation, water-soluble carbohydrate (WSC) concentration and herbage mass of juvenile ryegrass plants when grown in a Mediterranean environment. Seedlings of ryegrass were grown in nursery pots arranged side-by-side and located outside in the open-air to simulate a mini-sward in Experiments 1 and 2, and a mixture of annual ryegrass and subterranean clover (Trifolium subterraneum L.) was grown in a small plot field study in Experiment 3. Swards were defoliated mechanically with the onset of defoliation commencing within 28 d of germination. Frequency of defoliation ranged from one to nine leaves per tiller, whilst defoliation height ranged from 30 mm of pseudostem height that removed all leaf laminae in Experiment 1, to 50 mm of pseudostem height with some leaf laminae remaining post-defoliation in Experiments 2 and 3.A positive relationship between herbage mass of ryegrass, WSC concentration and leaf number per tiller at defoliation was demonstrated in all experiments. In Experiment 1, the herbage mass of leaf, pseudostem and roots of tillers defoliated at one leaf per tiller was reduced to 0·10, 0·09 and 0·06 of those tillers defoliated less frequently at six leaves per tiller. However, the reduction in herbage mass from frequent defoliation was less severe in Experiment 2 and coincided with a 0·20 reduction in WSC concentration of pseudostem compared with 0·80 measured during Experiment 1. In Experiment 3, the highest harvested herbage mass of ryegrass occurred when defoliation was nine leaves per tiller. Although the harvested herbage from this sward contained senescent herbage, the in vitro dry-matter digestibility of the harvested herbage did not differ significantly compared with the remaining treatments that had been defoliated more frequently.Leaf numbers of newly germinated ryegrass tillers in a Mediterranean environment were positively associated with WSC concentration of pseudostem and herbage mass. A minimum period of two to three leaf appearances was required to restore WSC concentrations to levels measured prior to defoliation thereby avoiding a significant reduction in herbage mass. However, maximum herbage mass of a mixed sward containing ryegrass and subterranean clover was achieved when defoliation was delayed to nine leaves per tiller.

Notes: In soil carbon dynamics, the role of physicochemical interactions between organic matter and minerals is not well understood nor quantified. This paper examines the interactions between soil organic matter and poorly crystalline aluminosilicates in a volcanic ash soil on La Réunion in the southern tropics. The soil examined is a profile composed of a surface soil (L-Ao-E-Bh) overlying four buried horizons (horizons 2Bw, 3Bw, 4Bw, 5Bw) that have all developed from successive tephra deposits. Non-destructive spectroscopy (XRD, FTIR and NMR of Si and Al) showed that the mineralogical composition varies from one buried horizon to another. Further, we show that buried horizons characterized by large amounts of crystalline minerals (feldspars, gibbsite) have the least capacity to store organic matter and the fastest carbon turnover. In contrast, buried horizons containing much poorly crystalline material (proto-imogolite and proto-imogolite allophane, denoted LP-ITM) store large amounts of organic matter which turns over very slowly. To understand the mechanism of interactions between LP-ITM and organic matter better, we focused on a horizon formed exclusively of LP-ITM. We demonstrate, using Δ14C and δ13C values, that even though LP-ITM is extraordinarily effective at stabilizing organic matter, C linked to LP-ITM is still in dynamic equilibrium with its environment and cycles slowly. Based on Δ14C values, we estimated the residence time of organic C as ∼ 163 000 years for the most stabilized subhorizon, a value that is comparable to that for organic carbon stabilized in Hawaiian volcanic soils. However, this calculation is likely to be biased by the presence of microcharcoal. We characterized the organo-mineral binding between organic matter and LP-ITM by 27Al NMR, and found that the organic matter is not only chelated to LP-ITM, but it may also limit the polymerization of mineral phases to a stage between proto-imogolite and proto-imogolite allophane. Our results demonstrate the important role of poorly crystalline minerals in the storage of organic C, and show that mineral and organic compounds have to be studied simultaneously to understand the dynamics of organic C in the soil.

Notes: The most southerly ombrotrophic peat bogs in Europe are in Galicia (northwest Spain). The humic matter in them originates from chemical processes in anaerobic conditions. We studied the acid properties of fulvic acids and humic acids isolated from two peat horizons of an ombrotrophic peat bog by potentiometric titration. Solutions containing 25, 50 and 100 mg l−1 of each humic substance were titrated at ionic strengths 0.005 m, 0.01 m and 0.1 m (with KNO3 as the inert electrolyte). Charge curves were analysed with a Donnan model to determine the intrinsic proton binding parameters. The concentration of the humic substance affected the charge curves more significantly at pH exceeding 6, and tended to disappear at greater concentrations. The proton binding conditional constants decreased with increasing ionic strength, this effect being more significant in the carboxylic groups with less affinity for protons. The proton binding constant of the carboxyl groups in a fulvic acid was one order of magnitude less than the value for the corresponding humic acid, whereas for the phenolic groups the values for both fractions were similar. The total content of acid groups was approximately 2 mol kg−1 greater in the fulvic fraction than in the humic fraction. Both humic fractions from the lower horizon contained more acid groups than those from the upper horizon, mainly because the content of carboxyl groups increases with soil depth. Therefore, the humic substances in the lower horizon of the peat will be more negatively charged, which will affect their solubility and the binding of metal ions.

Notes: Risk assessment of groundwater pollution requires quantitative information on the release kinetics of pollutants and organic matter from contaminated soil. We applied a new experimental design for column outflow experiments to investigate the release of polycyclic aromatic hydrocarbons (PAHs) and dissolved organic matter under water-saturated flow conditions. We used materials originating from a soil contaminated with non-aqueous phase liquids. To distinguish between release at equilibrium and release limited by mass transfer, we used two flow velocities and multiple interruptions to the flow. We quantified release and transport parameters by inverse numerical simulation of the individual breakthrough curves, applying a model based on the advection–dispersion equation including non-equilibrium and non-linear sorption. Release of the dissolved organic C takes place in two steps. Initially, a large amount of readily available organic matter is released. This first flush is followed by an outflow with typical characteristics of rate-limited release: larger concentrations in slower flow and increased concentrations after interruptions. The breakthrough of PAHs responds neither to the different flow velocities nor to the interruptions. We hypothesize that release of PAHs from the contaminated material is governed by dissolution at equilibrium according to Raoult's law. The boundary conditions of the experimental design, i.e. the flow velocities and multiple interruptions, enable us to distinguish between release at equilibrium and that which is rate-limited. Also, the response of the breakthrough behaviour to the boundary conditions can be used to estimate inversely effective release parameters.

Notes: Partitioning carbon (C) pools presents theoretical and practical challenges in soil modelling. In most current models, organic matter (OM) is commonly divided into a number of pools using data-fitting techniques. It is often not possible to measure the properties of each pool of soil C simulated in this way. Furthermore, there is no effective way in current soil models to properly simulate inputs of OM with variable qualities in terms of decomposability. Here, we describe a simple model, taking the OM as a whole and assuming a rate constant function changing exponentially with time, to simulate C decomposition in a multi-component OM pool. The model requires fewer parameters to be estimated than current multi-component models, and the simulated properties of OM are measurable. When changing the quantity and the quality of OM input, the model produces results similar to multi-component models, but avoids the difficulty and uncertainty of OM partitioning.

Notes: The estimation of soil carbon content is of pressing concern for soil protection and in mitigation strategies for global warming. This paper describes the methodology developed and the results obtained in a study aimed at estimating organic carbon contents (%) in topsoils across Europe. The information presented in map form provides policy-makers with estimates of current topsoil organic carbon contents for developing strategies for soil protection at regional level. Such baseline data are also of importance in global change modelling and may be used to estimate regional differences in soil organic carbon (SOC) stocks and projected changes therein, as required for example under the Kyoto Protocol to the United Nations Framework Convention on Climate Change, after having taken into account regional differences in bulk density.The study uses a novel approach combining a rule-based system with detailed thematic spatial data layers to arrive at a much-improved result over either method, using advanced methods for spatial data processing. The rule-based system is provided by the pedo-transfer rules, which were developed for use with the European Soil Database. The strong effects of vegetation and land use on SOC have been taken into account in the calculations, and the influence of temperature on organic carbon contents has been considered in the form of a heuristic function. Processing of all thematic data was performed on harmonized spatial data layers in raster format with a 1 km × 1 km grid spacing. This resolution is regarded as appropriate for planning effective soil protection measures at the European level. The approach is thought to be transferable to other regions of the world that are facing similar questions, provided adequate data are available for these regions. However, there will always be an element of uncertainty in estimating or determining the spatial distribution of organic carbon contents of soils.

Notes: Stones on the surface of the soil enhance infiltration and protect the soil against erosion. They are often removed in modern mechanized agriculture, with unfortunate side-effects. We evaluated experimentally the influence of surface stones on infiltration, runoff and erosion under field conditions using a portable rainfall simulator on bare natural soil in semi-arid tropical India, because modernization and mechanization often lead to removal of these stones in this region. Four fields with varied cover of stones from 3 to 65% were exposed to three rainfall intensities (48.5, 89.2 and 136.8 mm hour−1). Surface stones retarded surface runoff, increased final infiltration rates, and diminished sediment concentration and soil loss. The final infiltration ranged from 26 to 83% of rainfall when the rainfall intensity was 136.8 mm hour−1. The reduction in runoff and soil erosion and increase in infiltration were more pronounced where stones rested on the soil surface than where they were buried in the surface layer. The sediment yield increased from 2 g l−1 for 64.7% stone cover with rainfall of 48.5 mm hour−1 to 70 g l−1 for 3.5% stone cover with rain falling at 136.8 mm hour−1. The soil loss rate was less than 2 t ha−1 hour−1 for the field with stone cover of 64.7% even when the rainfall intensity was increased to 136.8 mm hour−1. The effects of stones on soil loss under the varied rainfall intensities were expressed mathematically. The particles in the sediment that ran off were mostly of silt size.

Notes: Phosphorus loss from land can be a major factor affecting surface water quality. We studied P-release mechanisms in wetland soils that had been drained and cultivated for four decades and then re-flooded. We measured redox, pH and solution composition in two sites in the field and in four peat and calcareous soils incubated in biogeochemical microcosms. The redox and pH measurements during the 120 days of incubation and the resulting soil solution composition indicated that the main process leading to P release is reductive dissolution of ferric hydroxides on which P was adsorbed and in which P was occluded. The molar Fe:P ratio increased with period of reduction from below 1 in the first week of re-flooding to 15–60 after 120 days. This suggests an increased P-retention capacity upon reoxidation of the soil solution, whether within the soil profile or in the drainage canals. Prolonged flooding of the calcite-poor, gypsum-rich peat soils increased the oversaturation of soil solutions with respect to hydroxyapatite and occasionally β-Ca3(PO4)2(c), indicating that in spite of the large Ca concentration, the rate of Ca-P precipitation was insufficient to maintain the saturation status of the Ca-P system. In the calcareous soils the Ca-P system effectively controlled the P activity in soil solution throughout the incubation period. In both cases the precipitation of Ca-P minerals could be an important P-retention mechanism.

Notes: Stable microaggregates can physically protect occluded soil organic matter (SOM) against decomposition. We studied the effects of agricultural management on the amount and characteristics of microaggregates and on SOM distribution in a marine loam soil in the Netherlands. Three long-term farming systems were compared: a permanent pasture, a conventional-arable system and an organic-arable system. Whole soil samples were separated into microaggregates (53–250 µm), 20–53 µm and 〈 20 µm organo-mineral fractions, sand and particulate organic matter, after complete disruption of macroaggregates. Equal amounts of microaggregates were isolated, irrespective of management. However, microaggregates from the pasture contained a larger fraction of total soil organic C and were more stable than microaggregates from the two arable fields, suggesting greater SOM stabilization in microaggregates under pasture. Moreover, differences in the relative contribution of coarse silt (〉 20 µm) versus fine mineral particles in the microaggregates of the different management systems demonstrate that different types of microaggregates were isolated. These results, in combination with micromorphological study of thin sections, indicate that the great earthworm activity under permanent pasture is an important factor explaining the presence of very stable microaggregates that are relatively enriched in organic C and fine mineral particles. Despite a distinctly greater total SOM content and earthworm activity in the organic- versus the conventional-arable system, differences in microaggregate characteristics between both arable systems were small. The formation of stable and strongly organic C-enriched microaggregates seems much less effective under arable conditions than under pasture. This might be related to differences in earthworm species' composition, SOM characteristics and/or mechanical disturbance between pasture and arable land.

Notes: Design and analysis of land-use management scenarios requires detailed soil data. When such data are needed on a large scale, pedotransfer functions (PTFs) could be used to estimate different soil properties. Because existing regression-based PTFs for estimating cation exchange capacity (CEC) do not, in general, apply well to arid areas, this study was conducted (i) to evaluate the existing models and (ii) to develop neural network-based PTFs for predicting CEC in Aridisols of Isfahan in central Iran. As most researches have found a significant correlation between CEC and soil organic matter content (OM) and clay content, we also used these two variables for modelling of CEC. We tested several published PTFs and developed two neural network algorithms using multilayer perceptron and general regression neural networks based on a set of 170 soil samples. The data set was divided into two subsets for calibration and testing of the models. In general, the neural network-based models provided more reliable predictions than the regression-based PTFs.

Notes: The distribution of iron-cyanide complexes between ferrocyanide, [FeII(CN)6]4–, and ferricyanide, [FeIII(CN)6]3–, in soils on contaminated sites depends on the redox potential, EH. We carried out microcosm experiments in which ferrocyanide (20 mg l−1) was added to an uncontaminated moderately acidic subsoil (pH 5.2), and varied the EH of the soil suspension between 200 and 700 mV over up to 109 days. Ferrocyanide and ferricyanide were analysed by capillary isotachophoresis. At redox potentials ranging from 400 to 700 mV, small amounts of iron-cyanide complexes were adsorbed, and ferrocyanide was almost completely oxidized to ferricyanide. Decreasing EH to 200 mV led to nearly complete removal of iron-cyanide complexes from solution, and the complexes were not mobilized after subsequent aeration (EH 〉 350 mV). Under weakly to moderately reducing conditions (EH ≈ 200 mV), iron-cyanide complexes were removed from solution by precipitation, which occurred, presumably in the form of e.g. Fe2[FeII(CN)6], Fe4[FeII(CN)6]3 or Mn2[FeII(CN)6], after reductive dissolution of Mn and Fe oxides. Four different sets of geochemical model calculations were carried out. The species distribution between ferrocyanide and ferricyanide in solution was predicted reliably under varying pH and redox conditions when iron-cyanide complex concentrations and Fe concentrations, excluding Fe bound in iron-cyanide complexes, were used in model calculations. In model calculations on the fate of iron-cyanide complexes in soil, adsorption reactions must be considered, especially under oxidizing conditions. Otherwise, the calculated iron-cyanide complex concentrations are larger than those actually measured.

Notes: Water movement in soil can be described accurately at the local scale, provided that soil hydraulic properties can be determined with precision. Traditional methods for characterizing soil are often time consuming, and large areas cannot be sampled easily. We present a simple method for overcoming these difficulties. It is easy to implement and cheap. It is known as the Beerkan method, and it relies on particle-size analysis, dry bulk density and simple infiltration tests in cylinders. We describe the experimental protocol and the method of data analysis, leading to the estimation of parameters describing hydraulic properties. Shape parameters depend on soil texture and are derived from particle-size data. Normalization parameters depend on soil structure. They are derived by inverse modelling and optimization from the infiltration tests. The theoretical background relies on the sorptivity concept and scaled forms of the infiltration equation. The formalism for one- and three-dimensional analysis is described. We assess the accuracy of the method using published data and simulated values, showing the soundness of the approach. For the purpose of illustration, we implemented a simple optimization technique on two bounding cases.

Notes: Fires in boreal forests frequently convert organic matter in the organic layer to black carbon, but we know little of how changing fire frequency alters the amount, composition and distribution of black carbon and organic matter within soils, or affects podzolization. We compared black carbon and organic matter (organic carbon and nitrogen) in soils of three Siberian Scots pine forests with frequent, moderately frequent and infrequent fires.Black carbon did not significantly contribute to the storage of organic matter, most likely because it is consumed by intense fires. We found 99% of black carbon in the organic layer; maximum stocks were 72 g m−2. Less intense fires consumed only parts of the organic layer and converted some organic matter to black carbon (〉 5 g m−2), whereas more intense fires consumed almost the entire organic layer. In the upper 0.25 m of the mineral soil, black carbon stocks were 0.1 g m−2 in the infrequent fire regime.After fire, organic carbon and nitrogen in the organic layer accumulated with an estimated rate of 14.4 g C m−2 year−1 or 0.241 g N m−2 year−1. Maximum stocks 140 years after fire were 2190 g organic C m−2 and 40 g N m−2, with no differences among fire regimes. With increasing fire frequency, stocks of organic carbon increased from 600 to 1100 g m−2 (0–0.25 m). Stocks of nitrogen in the mineral soil were similar among the regimes (0.04 g m−2). We found that greater intensities of fire reduce amounts of organic matter in the organic layer but that the greater frequencies may slightly increase amounts in the mineral soil.

Notes: The arrangement of a plant's roots in the soil determines the ability of the plant to resist uprooting. We have investigated the influence of root morphology on anchorage using simple patterns of root systems and numerical simulation. The form and mechanical properties of roots were derived from results found in the literature. Major parameters determining soil characteristics, root patterns and strength were varied so that their influence could be evaluated. The design of the experimental method we used generated an optimal number of configurations of different root systems, the tensile resistances of which were calculated by two-dimensional finite element analysis. We could quantify the influence of specific parameters, e.g. branching angle, number of lateral roots and soil cohesion, as well as global parameters such as total contact area, basal diameter and volume of the whole root system. We found that the number of roots and the diameter of roots were major components affecting the resistance to uprooting. The combination of topology and biomass explained 70% of the variation of tensile resistance.

Notes: The inability of physical and chemical techniques to separate soil organic matter into fractions that have distinct turnover rates has hampered our understanding of carbon (C) and nutrient dynamics in soil. A series of soil organic matter fractionation techniques (chemical and physical) were evaluated for their ability to distinguish a potentially labile C pool, that is ‘recent’ root and root-derived soil C. ‘Recent’ root and root-derived C was operationally defined as root and soil C labelled by 14CO2 pulse labelling of rye grass–clover pasture growing on undisturbed cores of soil. Most (50–94%) of total soil + root 14C activity was recovered in roots.Sequential extraction of the soil + roots with resin, 0.1 m NaOH and 1 m NaOH allocated ‘recent’ soil + root 14C to all fractions including the alkali-insoluble residual fraction. Approximately 50% was measured in the alkali-insoluble residue but specific activity was greater in the resin and 1 m NaOH fractions. Hot 0.5 m H2SO4 hydrolysed 80% of the 14C in the alkali-insoluble residue of soil + roots but this diminished specific activity by recovering much non-14C organic matter. Pre-alkali extraction treatment with 30% H2O2 and post-alkali treatment extractions with hot 1 m HNO3 removed organic matter with a large 14C specific activity from the alkali-insoluble residue.Density separation failed to isolate a significant pool of ‘recent’ root-derived 14C. The density separation of 14C-labelled roots, and roots remixed with non-radioactive soil, showed that the adhesion of soil particles to young 14C-labelled roots was the likely cause of the greater proportion of 14C in the heavy fraction.Simple chemical or density fractionations of C appear unsuitable for characterizing ‘recent’ root-derived C into fractions that can be designated labile C (short turnover time).

Notes: The physical characteristics of the soil at the root–soil interface are crucial because they determine both physical aspects of root function such as water and nutrient uptake and the microbial activity that is most relevant to root growth. Because of this we have studied how root activity modifies the structure and water retention characteristic of soil adjacent to the root for maize, wheat and barley. These plants were grown in pots for a 6-week growth period, then the soil adjacent to the root (rhizosphere soil) and bulk soil aggregates were harvested. These soil aggregates were then saturated and equilibrated at matric potentials between −600 kPa and saturation, and the water retention characteristics were measured. From subsamples of these aggregates, thin sections were made and the porosity and pore-size distributions were studied with image analysis. Both image analysis and estimates of aggregated density showed that the rhizosphere soil and bulk soil had similar porosities. Growing different plants had a small but significant effect on the porosity of the soil aggregates. Image analysis showed that for all the plant species the structure of the rhizosphere soil was different to that of the bulk soil. The rhizosphere soil contained more larger pores. For maize and barley, water retention characteristics indicated that the rhizosphere soil tended to be drier at a given matric potential than bulk soil. This effect was particularly marked at greater matric potentials. The difference between the water retention characteristics of the bulk and rhizosphere soil for wheat was small. We compare the water retention characteristics with the data on pore-size distribution from image analysis. We suggest that differences in wetting angle and pore connectivity might partly explain the differences in water retention characteristic that we observed. The impact of differences between the water retention properties of the rhizosphere and bulk soil is discussed in terms of the likely impact on root growth.

Notes: In highly weathered tropical conditions, soil organic matter is important for soil quality and productivity. We evaluated the effects of deforestation and subsequent arable cropping on the qualitative and quantitative transformation of the humic pool of the soil at three locations in Nigeria. Cultivation reduced the humic pool in the order: acetone-soluble hydrophobic fraction (HE) 〉 humic acid (HA) 〉 humin (HU) 〉 fulvic acid (FA), but not to the same degree at all three sites. The C and N contents, as well as the C/N ratios of humic extracts, were large and not substantially influenced by land use. The δ13C values of the humic extracts were invariably more negative in forested soils thereby showing a dilution of δ13C signature with cultivation from C3 to C4 plants. The δ13C values of apolar HE fractions were generally more negative, indicating a reduced sensitivity compared with other humic fractions to turnover of crop residues. The contents of hydrophobic constituents (alkyl and aromatic C), as revealed by cross-polarization magic angle spinning (CPMAS) 13C-NMR spectroscopy, in HA, FA and HU were generally 〈 50%, with the exception of larger hydrophobicity in HU in the forested soil at Nsukka and HA in that at Umudike. The HE fraction contained significantly more apolar constituents, and consequently had a larger intrinsic hydrophobicity than the other humic fractions. The larger reduction of apolar humic constituents than of the less hydrophobic humic fractions, when these soils were deforested for cultivation, indicates that at those sites the stability of accumulated organic matter is to be ascribed mainly to the selective preservation of hydrophobic compounds.

Notes: The value of nested sampling for exploring the spatial structure of univariate variation of the soil has been demonstrated in several studies and applied to practical problems. This paper shows how the method can be extended to the multivariate case. While the extension is simple in theory, in practice the direct estimation of covariance components by equating mean-square matrices with their expectation will often lead to estimates that are not positive semidefinite. This paper discusses solutions to this problem for balanced and unbalanced sample designs. In the balanced case there is a residual maximum likelihood (REML) estimator that will find estimates of covariance components that maximize an overall likelihood on the condition that all components are positive semidefinite (p.s.d.). This is possible because the condition is met if the differences of successive mean-square matrices are positive semidefinite, and this constraint can be incorporated into an algorithm. This does not hold for unbalanced designs. In this paper the problem was solved for unbalanced designs by scaling covariance components that were not p.s.d. to the nearest p.s.d. matrix according to a Euclidean distance.These methods were applied to data from three surveys, two with balanced and one with unbalanced sampling. Different patterns of scale-dependence of the correlation of soil properties were found. For example, at Ginninderra Experimental Station in Australia the soil water content and bulk density were correlated significantly, with the correlation increasing with distance to 56 m, but at longer distances the properties were not significantly correlated. By contrast, the pH of the soil and the available P content showed correlation that increased with distance. The implications of these results for planning more detailed sampling, both for prediction and for investigation of processes, are discussed.

Notes: Soils and sediments contain only small amounts of organic matter, and large concentrations of paramagnetic metals can give poor solid-state nuclear magnetic resonance (NMR) spectra of organic matter. Pretreatment of samples with hydrofluoric acid (HF) dissolves significant proportions of the mineral matrix and extracts paramagnetic elements. We investigated the effects of 10% HF treatment on the stable isotope content of carbon (C) and nitrogen (N) of organic matter from soils, composts and shales. Additionally we inferred molecular and isotopic characteristics of lost materials from calculations of isotope mass balances. Treatment with HF enriched C and N in mineral samples substantially (factors 2.5–42.4), except for Podzol B horizons (1.1–1.7) and organic material (1.0–1.3). After treatment most of the C (59.7–91.7%) and N (53.7–86.6%) was recovered, although changing C/N ratios often indicated a preferential loss of N-rich material. Isotope ratios of C and N in the remaining material became more negative when net alterations exceeded 0.3‰. The isotope ratios of the lost material contained more 13C (1–2‰) and 15N (1–4‰) than the initial organic matter. Acid hydrolysis typically removes proteins, amino acids and polysaccharides, all of which are enriched in 13C, and in the case of proteins and amino acids, enriched in 15N as well. We conclude that HF treatment released fresh, soluble, probably microbial, biomass in addition to carbohydrates. Net changes of the bulk chemical composition of organic matter were small for most soils, size fractions and plant material, but not for samples containing little organic matter, or those rich in easily soluble organic matter associated with iron oxides, such as Podzol B horizons.

Notes: Aromatic acids can reach the soil from direct anthropogenic activities or, indirectly, from the degradation of many aromatic compounds, such as pesticides or polycyclic aromatic hydrocarbons. Because of the anionic character of aromatic acids at the pH of most soil and sediment environments, they are expected to move rapidly through the soil profile and to pose a great risk of ground water contamination. We designed batch and column leaching tests to characterize the behaviour of three aromatic acids differing in their chemical structures, picloram (4-amino-3,5,6-trichloropicolinic acid), phthalic acid (2,2-benzenedicarboxylic acid), and salicylic acid (2-hydroxybenzoic acid), in four European soils with different physicochemical characteristics. Batch experiments revealed that the persistence of the three acids in soil:water suspensions decreased in the order: picloram ≫ phthalic acid 〉 salicylic acid, and their dissipation curves were relatively independent of soil type. Sorption by the soils, their clay-size fractions and model sorbents indicated much greater affinity of soil constituents for salicylic acid than for picloram or phthalic acid, most likely due to the ability of salicylic acid to form bidentate complexes with positively charged soil components. The extent of leaching of the aromatic acids in hand-packed soil columns decreased in the order: picloram (90–96%) 〉 phthalic acid (25–90%) 〉 salicylic acid (0–37%), which was consistent with the sorption and persistence results of the batch tests. The organic C content, the amount of small-size pores, and the initial concentration of aromatic acid in soil appeared to be important factors influencing the leaching patterns of phthalic acid and salicylic acid in the soils studied, but did not greatly influence the leaching pattern of picloram. Sorption and leaching of polar aromatic acids in soil can therefore vary considerably depending on the structural characteristics of the aromatic acid or soil type.

Notes: Preferential flow, as it bypasses the soil matrix, can greatly enhance the leaching of chemicals. When a soil is drained there is the risk that such short-circuiting results in more or less direct passage of polluting chemicals from the soil to the groundwater. If the groundwater table is shallow the chemicals could be transferred back into the surface soil by hydraulic lift through roots and subsequent release by exudation or from decaying plant residues and again become exposed to leaching by preferential flow, thus strongly enhancing the chance of export via the drains.We investigated the leaching of bromide in a tile-drained arable field over 2 years of crop rotation. The site was a former wetland, artificially drained a century ago for agriculture. Bromide was applied over 1.6 ha at a dosage of 10 g Br per m2 in August 1995 after the harvest of wheat. During the 2 years 18% of the applied bromide was exported via the drainage system, most of it in preferential flow events and more than half of it in a single winter storm 5 months after the application. Within 7 months 56% of the applied tracer was leached out of the main root zone into the groundwater. Subsequently the tracer re-emerged in water taken up by sugar beet in the following season. The beet accumulated 50% of the initially applied bromide in their leaves and released it again after harvest when the leaves were left as green manure on the field. Our results show that this recycling of solutes to the topsoil can have an important influence on their leaching as the solutes are thus again exposed to preferential transport into drains in the course of preferential flow events.

Notes: We tested the Rothamsted Carbon Model (RothC) against three long-term (27–28 years) experimental sites on Thai upland soils in order to see how this widely used ‘temperate’ soil carbon turnover model performed in a typical farming region in the tropics. We were able to verify – over a much longer period than had been examined in previous studies – that RothC performs well in a tropical region in plots used for continuous cropping experiments of maize and cassava without organic matter application. However, the model overestimated soil organic carbon (SOC) in some plots to which large amounts of organic matter (rice straw or cassava stalks) were applied. This overestimate could not be attributed to errors in estimating either the amount of C input to the soil or the ratio of decomposable plant materials to resistant plant materials entering the soil. Among many factors affecting SOC dynamics (e.g. weather conditions, soil characteristics, etc.), which are different in tropical regions from temperate regions, we conclude that the activity of soil fauna might be a major factor which makes the performance of RothC worse where much organic matter was applied. We suggest that care should be taken when applying RothC to tropical soils with large amounts of added organic matter.

Notes: Intact lysimeters (50 cm diameter, 70 cm deep) of silt loam soil under permanent grassland were used to investigate preferential transport of phosphorus (P) by leaching immediately after application of dairy effluent. Four treatments that received mineral P fertilizer alone (superphosphate at 45 kg P ha−1 year−1) or in combination with effluent (at ∼ 40–80 kg P ha−1 year−1) over 2 years were monitored. Losses of total P from the combined P fertilizer and effluent treatments were 1.6–2.3 kg ha−1 (60% of overall loss) during eight drainage events following effluent application. The rest of the P lost (40% of overall loss) occurred during 43 drainage events following a significant rainfall or irrigation compared with 0.30 kg ha−1 from mineral P fertilizer alone. Reactive forms of P (mainly dissolved reactive P: 38–76%) were the dominant fractions in effluent compared with unreactive P forms (mainly particulate unreactive P: 15–56%). In contrast, in leachate following effluent application, particulate unreactive P was the major fraction (71–79%) compared with dissolved reactive P (1–7%). The results were corroborated by 31P nuclear magnetic resonance analysis, which showed that inorganic orthophosphate was the predominant P fraction present in the effluent (86%), while orthophosphate monoesters and diesters together comprised up to 88% of P in leachate. This shows that unreactive P forms were selectively transported through soil because of their greater mobility as monoesters (labile monoester P and inositol hexakisphosphate) and diesters. The short-term strategies for reducing loss of P after application of dairy effluent application should involve increasing the residence time of applied effluent in the soil profile. This can be achieved by applying effluent frequently in small amounts.

Notes: Nitrogen (N) budgets were determined for six typical, moderately intensive dairy farms in south-west England. Proportionately, only 0·12–0·17 of the N input to the farms was recovered in agricultural products, leaving annual N surpluses equivalent to 249–376 kg N ha−1. A sequence of models (MANNER, NCYCLE and SUNDIAL) was used, together with the estimated N balance of the dairy cows and standard ammonia emission factors, to estimate N losses for each farm. Total estimated losses were equivalent to 137–220 kg N ha−1 year−1. Leaching accounted for 0·26–0·45 of the total loss, ammonia volatilization for 0·27–0·39 and denitrification for 0·17–0·36. When residual N from manure applications was included, there appeared to be an annual accumulation of soil N, equivalent to 66–158 kg N ha−1 when averaged over the whole farm area. The amounts of N lost by leaching, volatilization and denitrification, and accumulated as soil-N, were determined by a combination of farm properties, including N input, soil type, drainage, characteristics of the manure produced and type of fertilizer. The sum of estimated losses and change in N retained on the farm was between 0·85 and 1·11 of the N surplus (input minus output) determined from the farm budget. This suggests that losses and the change in soil-N were underestimated on some farms and overestimated on others (by up to −50 and +23 kg N ha−1 respectively). Much of the discrepancy between estimates and the surplus was attributed to difficulties of fully integrating inputs and outputs between the different models and stages of the modelling procedure.

Notes: Four perennial ryegrass (Lolium perenne L.) cultivars were compared for differences in herbage production, nutritive value and herbage intake of dry matter (DM) during the summers of 2002 and 2003. Two paddocks were sown with pure stands of four cultivars in a randomized block design with three replicates. Each plot was subdivided into fourteen subplots (22 m × 6 m) which were grazed by one cow during 24 h. Twelve lactating dairy cows were assigned to one cultivar for a period of 2 weeks in a 4 × 4 Latin square experimental design; the experiment lasted 8 weeks in each year. Sward structure (sward surface height, DM yield, green leaf mass, bulk density and tiller density) and morphological characteristics were measured. The ash, neutral-detergent fibre, acid-detergent lignin, crude protein and water-soluble carbohydrate concentrations, and in vitro digestibility of the herbage were measured. The sward was also examined for infestation by crown rust (Puccinia coronata f. sp. lolii). Herbage intake of dairy cows was estimated using the n-alkane technique. Cultivar differences for all sward structural characteristics were found except for bulk density and tiller density in 2003. Cultivars differed for proportions of pseudostem, stem (in 2003 only) and dead material. The chemical composition of the herbage was different among cultivars, with the water-soluble carbohydrate concentration showing large variation (〉0·35). Cultivars differed in susceptibility to crown rust. Herbage intake differed among cultivars in 2002 (〉2 kg DM) but not in 2003. Herbage intake was positively associated with sward height, DM yield and green leaf mass. Canopy morphology did not affect herbage intake. Crown rust affected herbage intake negatively. It was concluded that options for breeders to select for higher intake were limited. High-yielding cultivars and cultivars highly resistant to crown rust were positively related with a high herbage intake.

Notes: Single pugging events, which involve remoulding of the soil around the hooves of livestock during treading, of moderate or severe pugging intensity were imposed in plots in a long-term white clover-ryegrass pasture during spring, by using dairy cows at varying stocking rates (4·5 cows 100 m−2 for 1·5 or 2·5 h respectively). Changes in the growth and morphology of white clover were investigated over the following 12 months. Defoliation at approximately 3-week intervals was carried out by mowing. Annual herbage production was reduced following moderate and severe pugging proportionately by 0·16 and 0·34 compared with the non-pugged control treatment. The corresponding decreases in white clover production were 0·09 and 0·52 respectively. Annual perennial ryegrass production was reduced by 0·37 under severe pugging. Pugging had an immediate adverse effect on growth of white clover which persisted for up to 156 d, and coincided with a large decrease in the proportion of white clover in herbage over the same period (e.g. 0·40 vs. 0·12, in control and severely pugged treatments, respectively, on day 112). In comparison, recovery in ryegrass growth was apparent after 50 d in severely pugged treatments, indicating that white clover is more vulnerable to severe pugging than perennial ryegrass. Analysis of individual white clover plants extracted from turves (300 mm × 300 mm) showed that direct hoof damage, fragmentation and burial of stolons were the major factors which reduced white clover production, rather than the changes in soil physical properties measured. Morphological characteristics associated with plant size (e.g. stolon length, growing points, and leaf numbers) all decreased under pugging. The situation had reversed by late summer, with larger plants dominating pugged plots, and coincided with the recovery of the proportion of white clover in herbage. Strategic pasture management practices, such as restricted grazing and the use of stand-off pads when soils are overly wet, are suggested as means of minimizing treading damage to pasture and reducing negative impacts on the growth and productivity of white clover.

Notes: Berseem clover (Trifolium alexandrinum L.) was sown as an intercrop with oats (Avena sativa L.) at 0, 30, 60, 90 and 240 oats plants m−2 in May in 1999 and 2000 in Alberta, Canada. Forage yield and quality were measured at 10-d intervals between 35 and 88 d after planting (DAP). Yield is defined as the biomass above 6 cm of the soil surface. The dry-matter (DM) yield of berseem clover in sole crops increased by 5–10 g m−2 d−1 between 35 and 55 DAP and then increased by 21–28 g m−2 d−1 between 55 and 75 DAP. The DM yields of oats sown at 240 plants m−2 increased by 26–28 g m−2 d−1 over the whole period from 35 to 75 DAP. Oats were the dominant component in the intercrops, even at low densities of oats. Berseem clover grown with 60 oats plants m−2 received only 0·24 of the incident light when shading by oats peaked at 65 DAP. DM yields of berseem clover in intercrops with 60 oats plants m−2 averaged 0·14–0·32 of the yields of berseem clover sole crops. Between 35 and 88 DAP in 2000, the crude protein (CP) concentration of berseem clover sole crops declined linearly from 310 to 180 g kg−1 DM, and the CP concentration of oats exhibited a quadratic response, declining from 350 g kg−1 DM at tillering to 110 g kg−1 DM at the soft dough stage. The mean CP concentration of berseem clover in intercrops with 60 oats plants m−2 was 25 g kg−1 less than in berseem clover sole crops, indicating that competition by oats reduced the CP concentration of berseem clover. At later sampling dates, CP and DM yields of intercrops with oats at 60 plants m−2 equalled those with oats at 240 plants m−2. The addition of berseem clover to oats in intercrops at 60 oats plants m−2 reduced the neutral-detergent fibre concentration by 30 g kg−1 DM compared with oats alone. Oats were very competitive as a companion crop for berseem clover. Adding berseem clover to oats increased forage quality and may provide for increased intake and digestibility of forage to support higher livestock productivity.

Notes: The botanical composition, intake and digestibility of the diet consumed by 1-year-old weaner sheep grazing a native white grass plant community in the Falkland Islands was measured in five periods between June 1998 and March 1999. Five different sheep were used in each period. Two methods were used for estimating the botanical composition of the diet: plant cuticle patterns in the faeces of the sheep and the patterns of concentrations of n-alkanes in the faeces of sheep. These methods were used to predict the concentrations of C32- and C33-alkanes in the herbage to allow the estimation of herbage intake and digestibility using the n-alkane technique. It was concluded that the n-alkane technique gave more accurate estimates of diet composition based on the comparison with estimates of nutrient intake derived from liveweight gains of sheep. The dominant pasture species, Cortaderia pilosa, was the predominant species consumed during the cooler periods of the year. In the summer, when the highest liveweight gains of sheep occur, the proportion of fine grass species, including Poa spp., Festuca magellanica and Agrostis capillaris, and herbs and sedges in the diet was highest. Herbage intake was the highest during the summer periods when digestibility was also at its peak. Estimated nutritional deficiencies of metabolizable energy, crude protein, phosphorus and vitamin D3 that limit the growth and development of weaner sheep were evident for up to 9 months of the year. Targeted supplementation regimes that counter specific nutrient deficiencies could be developed on the basis of these results to address critical periods in the growth of young sheep.

Notes: Crop composition at harvest affects the ensiling process and the resulting silage quality. The objectives of this study were to determine: (i) the effect of annual N-fertilizer application (0, 60, 120 and 180 kg N ha−1) and developmental stage (stem elongation, early heading, late heading and early flowering) on the ensiling properties and silage quality of the spring regrowth of timothy (Phleum pratense L.) at two sites for 1 or 2 years, and (ii) the relationship between ensiling properties of the forage and the quality of the resulting silage. Laboratory silos with wilted forage at approximately 350 g dry matter (DM) kg−1 of fresh matter were prepared at each harvest and opened 150 d later for silage analysis. Higher rates of N-fertilizer application decreased the concentration of water-soluble carbohydrates (WSC), increased the buffering capacity (BC) and nitrate concentration, and decreased the ratio of WSC:BC, primarily in the early stages of development. The ensiling properties of timothy were, therefore, less favourable when high rates of N fertilizer were applied. Silage pH generally increased with increasing rates of N-fertilizer application; this increase was particularly evident at the first three developmental stages at one site in 1 year. Non-protein N (NPN) and soluble N concentrations of the silages increased with increased rates of N-fertilizer application at the first three developmental stages but decreased at early flowering. Ammonia-N concentration in the silages increased by 0·85, 0·56 and 0·67 when rates of N-fertilizer application were 60, 120 and 180 kg ha−1, respectively, compared with that when no N fertilizer was applied. Significant correlations between the composition of the forage ensiled and silage quality variables were found at sites in individual years but, when all data were combined, WSC concentration and BC, and their ratio in the forages, were not correlated with pH, and soluble-N and ammonia-N concentrations of the silages, and were weakly correlated with NPN and free amino acid-N concentrations of the silages. Silage quality was reduced by increased N-fertilizer application, primarily at the early developmental stages, and this can be attributed to a reduction in WSC concentration and an increase in BC of the forage. Water-soluble carbohydrate concentration, BC, and their ratio, however, were poor predictors of silage quality.

Notes: A model that describes the utilization of herbage by cattle in a rotational grazing system is presented. The model considers swards as being structured into two phases: a long phase associated with old dung patches, and a short phase. Both phases are treated as consisting of a series of horizontal strata corresponding in depth to a bite depth. The sward is divided into feeding stations consisting of either the long or the short phase. In each, only the surface stratum is available for grazing at each time step. At any time step, the individuals of a herd of cattle, distributed at random, encounter the entire range of strata. The rate of intake of each member of the herd depends on the intake properties of the stratum that it has encountered. The number of cattle that encounter each stratum type is variable so that the mean intake per member of the herd is the weighted mean. The core feature of the model is the simulation of the change over time in the frequency distribution of exposed stratum types and the distribution of grazing across this range of strata. The members of the herd are assumed to select a feeding station based on preference for leafiness of the encountered stata and the phase. The decision to graze or not is based on the comparison between the current vs. the previous feeding station. Model parameter values were based on published data. The proportion of leaf and bulk density of a phase or the strata were determined from an analysis of a sample of sward profiles. Using bite dimension, bite weight, biting rate, search time, feeding station area and selective behaviour, it was possible to simulate sward depletion that is very similar to the observed data from grazed paddocks in experiments in south-east Ireland. The model of herbage utilization adequately described the changes in intake and sward structure during grazing and it was concluded that it was suitable for use as part of a simulation of a grazing system.

Notes: Upland hay meadows conforming to MG3 in the National Vegetation Classification of the UK are a rare habitat in Britain and are largely confined to upland valleys in northern England. Agricultural intensification, particularly ploughing and reseeding and a shift from hay-making to silage production over the last 50 years, has resulted in large losses of species-rich upland hay meadows. Remaining species-rich meadows have been the focus of much nature conservation effort resulting in many of the species-rich sites being protected by statutory designations or through voluntary agri-environment scheme agreements. Research and monitoring has tended to confirm that species richness is maximized by management involving spring and autumn grazing, a mid-July hay cut, no inorganic fertilizer and possibly low levels of farmyard manure. Deviations from this regime result in a loss of species richness. Restoration of semi-improved grassland to swards resembling species-rich MG3 also requires a similar regime but is also dependent on the introduction of seed of appropriate species. The role of Rhinanthus minor as a tool for manipulating meadow biodiversity during restoration management is discussed. Suggestions for future research are outlined.

Notes: Agrostis capillaris, Arrhenatherum elatius, Bromus willdenowii, Cynosurus cristatus, Dactylis glomerata, Elytrigia repens, Lolium multiflorum, L. perenne, Phalaris aquatica, Phleum pratense, Schedonorus phoenix, and a ryegrass selected for high surface root mass, were grown in 1 m deep × 90 mm diameter tubes of sand. Tubes were irrigated with a low ionic-strength nutrient solution and 15N-labelled nitrate was leached down the tubes prior to harvest. Shoot weights, root weights in 10-cm depth increments, and shoot and root nitrogen concentrations were determined. Plants of L. multiflorum were the heaviest and plants of A. capillaris were the lightest. Root system shape was analysed by comparing the decay constant from an exponential model fitted to the proportion of root mass in 10-cm depth increments, and, also, by analysis of the proportion of root mass in the top 10 cm. Cynosurus cristatus was strongly surface-rooted and the perennial ryegrass, selected for high surface root mass, had more root mass between 0 and 10 cm than did the unselected perennial ryegrass cultivar. There were only small differences in root shape between the other grasses. There was a strong and positive correlation between plant dry weight and the proportion of the pulse of labelled nitrate that was intercepted. The variation in root system shape shown in this experiment had no effect on nitrate interception. Nitrate interception per unit root weight was significantly higher in A. capillaris than in the other grasses. Developing winter-active grasses that have finely divided root systems should contribute to pastures with better nitrate retention characteristics.

Notes: The effects of five rates [0 (control), 1, 2, 4 and 6 Mg ha−1] of calcium silicate on the growth and water consumption by rhodes grass (Chloris gayana Kunth) and sudan grass (Sorghum sudanense Piper) under wet and dry soil water regimes (60 g and 30 g H2O kg−1 soil respectively) were evaluated in a pot experiment. The effect of the application of silicate on plant biomass was similar to that of the control. However, the shoot and root dry mass varied significantly (P 〈 0.001) according to the soil water regime and plant species. During the first cut, the shoot dry mass was 5.7 g per pot under the wet soil moisture regime, significantly exceeding that under the dry soil water regime proportionately by 0.68. For sudan grass, the shoot dry mass varied from 3.6 g per pot in the control to 4.3 g per pot in the treatment that received 6 Mg ha−1 of calcium silicate. Plant water demand decreased as the rate of calcium silicate application increased, suggesting that an application of calcium silicate could reduce drought stress and enhance water economy. For the soil under study, the reduction in plant water demand represents a water saving ranging from 0.076 to nearly 0.20.

Notes: A simulation model was used to compare the long-term performance of cow-calf farm systems under different haymaking strategies on a 100-ha farm. In the simulation, farm management was based on that which had been developed on Reserva 6, an experimental cow-calf farm established in 1966 at Instituto Nacional de Tecnología Agropecuaria-Balcarce Experimental Station, Argentina, where different technologies, including haymaking, have been adapted and applied in order to increase productivity of cow-calf systems in the Salado Region of Argentina. The management of the system is based on a restricted mating season (2 months), early weaning (5–7 months of age) and forage conservation. The simulations showed that the effect of using hay with respect to the strategy without hay, in terms of calf liveweight (LW) production per hectare, was greatest at the cow numbers that maximized production (290–320 cows) with a proportionate increase of 0.25. On the other hand, the advantage of using hay was smallest when the herbage mass at cutting for hay was 6 t dry matter (DM) ha−1, particularly when more than 0.50 of the farm area was allocated to haymaking. The differences among the haymaking policies increased with cow numbers, especially at high herbage masses at cutting for hay. The analysis also suggested that the LW production per hectare of cow-calf farms would be maximized by harvesting 0.40–0.50 of the total farm area and aiming to cut hay at a herbage mass of 4 t DM ha−1 and with medium quality.

Notes: Risk and cost estimates, calculated using a weather-driven farm simulation model, were used to evaluate the impact of different haymaking strategies in dryland cow-calf systems such as those in the Salado region of Argentina. Based on a 100-ha farm, each strategy was simulated using twenty sequences of 50 years of random weather. A risk-efficiency methodology was used, using calf live weight sold and considering the economic value of the live weight produced per year minus the cost of haymaking, as a simple measure of profit. The analysis highlighted both production and risk advantages in using hay, especially when a flexible hay management approach was implemented, although some haymaking strategies performed worse than not using hay. When calf live weight sold was considered alone, the risk-efficient set included strategies with large proportions of the areas being harvested (0.42–1.05; paddocks could be cut more that once a year in some of the strategies) and high proportions of hay not being used. The amount of hay for maximizing risk efficiency for profit was notably lower than that for maximizing cattle production. When haymaking costs were included, the proportion of area harvested for risk-efficient profit ranged from 0.28 to 0.52, depending on the target stocking rate.

Notes: In pastoral farming systems, pasture production normally exceeds demand in the spring–summer period. Consequently, conserving forage at this time for use during the following winter is a widespread practice. The objective of this study was to assess the possible advantages of incorporating flexibility into a calendar-based haymaking policy. A range of flexible haymaking strategies were simulated and compared against a calendar-based strategy by using a simulation model to estimate long-term performance of cow-calf farm systems under each strategy. The results suggest that controlling haymaking in a flexible fashion, basing the decisions of closing, releasing and cutting paddocks on a simple pasture budget, could give the system productive advantages over using a calendar-based approach. In terms of liveweight production per hectare, compared at the same area harvested, the flexible approach had higher average annual calf liveweight production (an increase of up to 0.15) and lower system variability [a reduction of 0.10 in the coefficient of variation (CV)] depending on the stocking rate. The results indicated that allocating more than 0.50–0.60 of the farm area to conservation would only be advantageous at very high stocking rates. In contrast to the calendar-based strategy, making more hay than required for the immediate next winter, where possible, can reduce system variability.