Degradation of estrogenic hormones in a silt loam soil

Estrogenic hormones are endocrine-disrupting compounds, which disrupt the endocrine system function of animals and humans by mimicking and/or antagonizing endogenous hormones. With the application of sludge biosolid and animal manure as alternative fertilizers in agricultural lands, estrogens enter the soil and become an environmental concern. The degradation kinetics of 17beta-estradiol, an estrogenic hormone of major concern, in a silt loam soil were investigated in this study. It was found that 17beta-estradiol degraded rapidly in nonsterilized soil with a half-life of 0.17 day. The degradation rate constant was proportional to the percentage of nonsterilized soil, indicating that microorganisms are directly responsible for the rapid degradation of 17beta-estradiol in soil. The half-life of 17beta-estradiol in 20% nonsterilized soil was slightly shortened from 1.3 to 0.69 day with the increase of soil moisture from 10 to 20% and was greatly decreased from 4.9 to 0.92 day with the increase of temperature from 15 to 25 degrees C. The coexistence of 40 micromol kg (-1) sulfadimethoxine, a veterinary antibiotic, decreased the degradation rate constant of 17beta-estradiol from 0.750 +/- 0.038 to 0.492 +/- 0.016 day (-1). The degradation kinetics of another three estrogenic hormones, including 17alpha-estradiol, estrone, and estriol, were also investigated and compared. Estrone was identified as a degradation product of 17beta-estradiol and the most persistent hormone among the four investigated estrogens. Estriol was observed in the degradation of estrone and 17alpha-estradiol.     

Activity,origins and location of cellulases in a silt loam soil

Summary Cellulase activity in a silt loam soil was assayed and characterised using a microcrystalline cellulose substrate (Avicel). Activity was maximal between pH 5.3 and pH 6.0. A 64% loss in activity was observed on air-drying the soil. However, the residual activity was stable to storage at 40°C for 7 days and was resistant to the action of added protease. The component endoglucanase and -D-glucosidase activities in field-moist and air-dried soil were also assayed. The proportion of the soil microbial population able to utilise cellulose was investigated and the persistence of two free (soluble) cellulase preparations of microbial origin was determined following their addition to soil. A rapid decline in the endoglucanase activity of a Streptomyces sp. cellulase preparation was observed while 30% of the original activity of a Trichoderma viride cellulase preparation could still be detected after 20 days. From the data obtained in this study it appears that the major portion of the -D-glucosidase activity is bound to and protected by the soil colloids. By contrast, the major portion of the exo- and endoglucanase activity appears to be free in the soil solution, attached to the outer surfaces of cellulolytic microorganisms or associated in enzyme substrate complexes. The low residual activity measured in air-dried soil may owe its stability to an association with soil colloids or with recalcitrant cellulosic material present in soil.     

Lumbricid macrofauna alter atrazine mineralization and sorption in a silt loam soil

Atrazine is a widely used herbicide and is often a contaminant in terrestrial and freshwater ecosystems. It is uncertain, however, how the activity of soil macrofauna affects atrazine fate and transport. Therefore, we investigated whether earthworms enhance atrazine biodegradation by stimulating herbicide degrading soil microflora, or if they increase atrazine persistence by facilitating herbicide sorption. Short (43 d) and medium term (86 d) effects of the earthworms Lumbricus terrestris and Aporrectodea caliginosa on mineralization, distribution, and sorption of U-ring-¹⁴C atrazine and on soil C mineralization was quantified in packed-soil microcosms using silt loam soil. A priming effect (stimulation of soil C mineralization) caused by atrazine supply was shown that likely lowered the earthworm net effect on soil C mineralization in atrazine-treated soil microcosms. Although earthworms significantly increased soil microbial activity, they reduced atrazine mineralization to ¹⁴CO₂-C from15.2 to 11.7% at 86 d. Earthworms facilitated formation of non-extractable atrazine residues within C-rich soil microsites that they created by burrowing and ingesting soil and organic matter. Atrazine sorption was highest in their gut contents and higher in casts than in burrow linings. Also, gut contents exhibited the highest formation of bound atrazine residues (non-extractable atrazine). Earthworms also promoted a deeper and patchier distribution of atrazine in the soil. This contributed to greater leaching losses of atrazine in microcosms amended with earthworms (3%) than in earthworm-free microcosms (0.003%), although these differences were not significant due to high variability in transport from earthworm-amended microcosms. Our results indicated that earthworms, mainly by casting activity, facilitated atrazine sorption, which increased atrazine persistence. As a consequence, this effect overrode any increase in atrazine biodegradation due to stimulation of microbial activity by earthworms. It is concluded that the affect of earthworms of atrazine mineralization is time-dependent, mineralization being slightly enhanced in the short term and subsequently reduced in the medium term.     

Direct drilling,shallow tine-cultivation and ploughing on a silt loam soil, 1974–1980

Results are given for an experiment in which direct drilling, shallow tine-cultivation and ploughing were compared on a silt loam soil over 7 years. A rotation of cereal and oilseed rape crops was established to minimise a possible interaction between disease, particularly take-all (Gaeumannomyces graminis), and cultivation treatment. Over the six harvest years shallow tillage produced on average a 6 and 9% heavier yield than ploughing and direct drilling, respectively. The importance of surface soil conditions at the time of seedling establishment was clearly evident. In years when the passage of the direct drill caused little soil disturbance and seeds were placed in a smeared slot, and particularly when crop residues were pressed into the slot, plant populations were diminished and so were yields. The degree of soil shattering by the passage of the drill and the consequent friability of the tilth varied between the extremes of water content of the top soil (0–5 cm). Direct drilling produced larger yields relative to ploughing after the first three seasons and this may reflect the increased organic matter content and stability of the soil aggregates in the surface layer (0–2.5 cm) which have already been reported for this soil. These changes may have facilitated the greater friability of the soil and the creation of tilth by the passage of the drill which ensured uniform germination and rapid establishment of the seedlings.The site was characterised by variations in the depth of topsoil over gravel (< 50 to > 100 cm), and the deepest soil gave the heaviest yield. This effect was relatively greater in dry seasons but it never interacted with the effect of tillage method.     

Poultry litter and tillage influences on corn production and soil nutrients in a Kentucky silt loam soil

Broiler chicken (Gallus gallus) manure, a rich source of plant nutrients, is generated in large quantities in southeastern USA where many row crops, such as corn (Zea mays L.), are also extensively grown. However, the use of broiler manure as an economical alternative source of nutrients for corn production has not been extensively explored in this region. This study was conducted to examine the use of broiler litter as a source of nutrients for corn production, as influenced by tillage and litter rate, and any residual effects following application. In addition, the consequence of litter application to soil test nutrient levels, particularly P, Zn and Cu, was explored. The treatments consisted of two rates of broiler litter application, 11 and 22 Mg ha⁻¹ on a wet weight basis, and one rate of chemical fertilizer applied under no-till and conventional tillage systems. Treatments were replicated three times in a randomized complete block design. Corn was grown with broiler litter and inorganic fertilizer applied to the same plots each year from 1998 to 2001. In 2002 and 2003, corn was planted no-till, but only N fertilizer was applied in order to make use of other residual litter nutrients. Soil samples were taken yearly in the spring prior to litter application and 4 years after the cessation of litter application to evaluate the status of the residual nutrients in soil. Two years out of the 4-year experiment, broiler litter application produced significantly greater corn grain yield than equivalent chemical fertilizer application and produced similar grain yield in the other 2 years. Corn grain yield was significantly greater under no-till in 1999, but significantly greater under conventional-till in 2000, and no difference between the two tillage systems were observed in 1998 and 2001. With 4 years of litter application, Mehlich-3 P increased from an initial 18 mg kg⁻¹ to 156 mg kg⁻¹ with 11 Mg ha⁻¹ litter and to 257 mg kg⁻¹ with 22 Mg ha⁻¹ litter. For every 6 kg ha⁻¹ of P applied in poultry litter Mehlich-3 P was increased by 1 mg kg⁻¹. Modest increases in Mehlich-3 Cu and Zn did not result in phytotoxic levels. This study indicated that an optimum rate of broiler litter as a primary fertilizer at 11 Mg ha⁻¹ applied in 4 consecutive years on a silt loam soil produced corn grain yields similar to chemical fertilizer under both no-till and conventional tillage systems and kept soil test P, Cu and Zn levels below values considered to be harmful to surface water quality or the crop.     

Aggregate stability and microbial community dynamics under drying-wetting cycles in a silt loam soil

Aggregate stability often exhibits a large inter-annual and seasonal variability which occurs regardless of residue treatments and is often larger than the differences between soils or cropping systems. Variations in soil moisture and seasonal stimulation of microbial activity are frequently cited as the major causes. The goal of this paper was to evaluate the effects of drying-rewetting cycles on aggregate stability and on its main microbially mediated agents from a mechanistic point of view. The 3-5 mm aggregates of a silty soil were incubated at 20 °C for 63 days with the following treatments and their combinations: (i) with or without straw input and (ii) with or without exposure to four dry-wet cycles. Microbial activity was followed by measuring the soil respiration. We estimated the microbial agents of aggregate stability measuring hot-water extractable carbohydrate-C, microbial biomass carbon and ergosterol content. We measured the water drop penetration time to estimate the hydrophobicity and aggregate stability according to Le Bissonnais [1996. Aggregate stability and assessment of soil crustability and erodibility: I. Theory and methodology. European Journal of Soil Science 47, 425-437] to distinguish three breakdown mechanisms: slaking, mechanical breakdown and microcracking. The addition of straw stimulated microbial activity and increased the resistance to the three tests of aggregate stability, enhancing the internal cohesion and hydrophobicity of aggregates. All the estimated microbial agents of aggregate stability responded positively to the addition of organic matter and were highly correlated with aggregate stability. Fungal biomass correlated better with aggregate stability than total microbial biomass did, showing the prominent role of fungi by its triple contribution: physical entanglement, production of extracellular polysaccharides and of hydrophobic substances. Dry-wet cycles had less impact on aggregate stability than the addition of straw, but their effects were more pronounced when microbial activity was stimulated demonstrating a positive interaction.     

Relationships between soil macroaggregation and humic carbon in a sandy loam soil following conservation tillage

Purpose

Humic substances are recalcitrant and might act as persistent binding agents to form macroaggregates. The focus of this study is in investigating the contribution of humic carbon (HC) to soil aggregation in response to various tillage and residue managements.

Materials and methods

Arable soils following 8-year contrasting managements were collected to determine aggregate size distribution and stability and HC fractions including humic acid (HA) and fulvic acid (FA). The contribution of HC to aggregation was divided into three special effects including positive effect (PE), negative effect (NE), and combined effect (CE), and these effects were measured using aggregate fractionation techniques.

Results and discussion

As well as to promote structural stability, HC bounds predominantly with the silt + clay fraction and secondarily with microaggregates to form larger aggregates. The PE increased with increasing aggregate size, whereas the NE followed the opposite pattern. A positive CE was observed for large and small macroaggregates, whereas the CE for microaggregates and the silt + clay fraction was negative. Compared to continuous tillage, reduced- and no-tillage decreased the PE for large and small macroaggregates by 1.58–30.98% at the 0–20 cm depth, and straw returning also slightly decreased the corresponding PE relative to straw removing. By contrast, a significantly higher NE for small macroaggregates at the 0–10 cm depth while 6.33–81.11% decreases in CE for large and small macroaggregates at the 0–10 cm depth as well as for large macroaggregates at the 10–20 cm depth, were observed under reduced- and no-tillage. The extraction of HC significantly reduced the aggregate stability and reduced- and no-tillage effectively limited its decrease magnitude. Small macroaggregates and microaggregates made larger contributions to soil HC accumulation than did other fractions. An averagely increased contribution from large or small macroaggregates was observed under both reduced-/no-tillage and straw returning at the 0–20 cm depth. A significant and positive relationship was found between the mass proportion of macroaggregates and the HC accumulation in 0–20 cm soil. Large macroaggregates had significantly higher HA/FA ratios than small macroaggregates, and reduced- and no-tillage significantly increased these ratios both in large and in small macroaggregates. The CE for large or small macroaggregates was also significantly negatively correlated with their HA/FA ratios.

Conclusions

Overall, the HC accumulation in soil is likely to play a key role in macroaggregation, but conservation tillage might decrease the contribution magnitude of HC to large or small macroaggregation through increasing the corresponding HA/FA ratios.

     

Physical and morphological characterization of undisturbed and disturbed ploughpans in a sandy loam soil

In a sandy loam soil the ploughpan had a lower porosity and a higher bulk density and mechanical resistance than ploughpans that had been disturbed by rota-digging two years previously. Hydraulic conductivities (K) for pressure heads (h) from 0 to ?20 cm were higher and moisture contents within the same h range were lower. Both values were identical for pressure heads lower than ?20 cm. According to the widely used physical capillary pore model, the volume of pores > 140 μm was 2% (v/v) in the undisturbed ploughpan and 8% (v/v) in the disturbed ploughpan. However, micromorphometric analyses showed that the undisturbed ploughpan contained the highest volume of large pores and many continuous root channels, while the disturbed ploughpan had no continuous large pores. Pore continuity was determined by using a staining test with methylene blue. Disturbance of the ploughpan in these soils results in formation of unstable fragments, which collapse, thereby disrupting the vertical continuity of the initially large packing voids between fragments.     

Effects of the phenylamide fungicides, mefenoxam and metalaxyl, on the microbiological properties of a sandy loam and a sandy clay soil

The objective of the study was to compare ecotoxicological data obtained from laboratory experiments on the side-effects of three phenylamide fungicides, pure metalaxyl (racemic mixture of R- and S-enantiomers), formulated metalaxyl and mefenoxam (only active R-enantiomer) on the chemical and biochemical parameters of two soils of different type and origin. The purpose of the comparison was to determine to what extent mefenoxam, developed as alternative to metalaxyl, can affect the activity of soil micro-organisms and their processes, and to elucidate the differences between the effects of pure and formulated metalaxyl. The dynamics of the quantitative changes in biochemical parameters induced by the addition of these fungicides at their recommended field rate were determined in a sandy clay soil from Cameroon and a sandy loam soil from Germany, during a 120-day incubation experiment. The type of soil significantly influenced the effect of these fungicides on the soil parameters studied. Incorporation of these fungicides generally stimulated the activity of phosphatases and ß-glucosidase, mineralization and the availability of N and most plant nutrients in soils. The activity of dehydrogenase and the availability of NO₃^- were generally adversely affected. Among the fungicides tested, the stimulation was more pronounced with mefenoxam followed by formulated metalaxyl.     

Composted biosolids enhance fertility of a sandy loam soil under dairy pasture

Field and pot trials were established to assess potential benefits and adverse effects of amending a sandy loam soil, under grazed ryegrass-clover pasture, with compost manufactured from wastewater biosolids, wood waste and green waste. Compost was applied to the field trial site annually for 4 years and the pot trials used soil from the field trial site each year after compost application. The pot trials demonstrated that yield of silver beet (Beta vulgaris L.) increased with increasing compost application rate and that plant metal uptake was (except for Zn) unrelated or inversely related to soil metal concentrations. In samples from the field trial, soil total C, N, P and Olsen P increased markedly with increasing compost application rate. Cation exchange capacity, exchangeable cations and total-extractable and EDTA-extractable metals (Cd, Cr, Cu, Ni, Pb and Zn) were also elevated, total Cu to the limit allowable in biosolids-amended soil. Soil basal respiration, microbial biomass C and anaerobically mineralisable N were significantly increased in the amended plots. Anaerobically mineralisable N was highly correlated with respiration (r =0.98, n =24) and only weakly related to microbial biomass C, probably indicating that a high proportion of the N mineralised was from the compost organic matter. Sulphatase and phosphatase activities increased, but not significantly, and there were no measurable effects on rhizobial numbers or on sensitive microbial biosensors (Rhizotox C and lux-marked Escherichia coli). Biosolids compost application enhanced soil fertility, productivity and microbial biomass and activity, with no apparent adverse effects attributable to heavy metals.     

Aggregate stability of a silt loam soil as affected by roots of corn,soybeans and wheat

Abstract

A greenhouse experiment was conducted to investigate the effect of root growth and exudation of 3 crop species on soil aggregation. Two plant populations for each of 3 crops (corn, soybeans, and wheat) were grown in a Fincastle silt loam for 5 time periods (7, 14, 21, 28, and 41 days) and compared with fallow controls. Aggregate stability was estimated by the wet‐sieve method on both initially moist and air‐dry samples.

Soil water content of initially moist soil samples varied widely among replicates, crops, and sampling dates. Wet‐sieving using initially moist soil showed that samples with higher initial soil water content had greater aggregate stability. Wet‐sieving performed on initially air‐dry soil samples was used for subsequent interpretation because the water content variable was removed.

The presence of any crop and its roots in the planted soils versus the fallow controls was associated with increases in aggregate stability. No differences in aggregate stability were found among the different crops or over the established range of root length densities. Aggregate stability decreased from the original level during the first 14 to 21 days of the experiment, possibly due to daily watering. After 21 days, as root growth continued to increase, restabilization occurred until the original aggregate stability of the soil was exceeded for all crops. The observed increase in aggregate stability may be due in part to the physical entanglement of aggregates by roots and to the increased production of root exudates resulting from increased root growth.     

Adsorption of sulphate by a sandy loam soil (calcic cambisol)

An arable sandy loam had an appreciable sulphate-adsorping capacity. This was fully reversible over short periods, but not over periods of days. This property was associated with the presence of haematite-containing particles of uncertain origin, but wide distribution in this and other Oxford soils. The adsorption of sulphate on the outer surfaces of these particles was reversible, but adsorption on fresh surfaces exposed by grinding was largely irreversible.     

Tillage effects on rain-generated wetting front migration through a Griswold silt loam soil

Information on the effects of different conservation tillage treatments on rain-generated wetting front migration (WFM) through layered soils is limited. In this study, conducted on a Griswold silt loam soil (Typic Argiudoll) formed in loess overlaying glacial till, the effects of three conservation tillage (CT) treatments: chisel (CH); no-tillage (NT); and till-plant (TP); were compared with conventional moldboard plowing (CN) on rain-generated EFM.

Different rainstorm patterns (amount and duration) had different effects of WFM through soil profiles of the different tillage treatments. Irrespective of storm duration, wetting fronts were observed to migrate faster in CH and NT treatments during larger storm events (> 20 mm) but only in NT treatment during storm events > 5 and < 15 mm. Smaller rainstorms (< 5 mm) did not generate WFM in any of the four tillage treatments. Wetting front migration during storm events > 5 and < 15 mm did not advance beyond 15 cm depth in CH, CN, and TP, but were noted to the 64-cm depth in NT. Wetting front migration for larger storms were observed to pass the 75-cm depth in all treatments. However, NT (with conductive micropores) saturated much quicker than the other treatments, suggesting that it might generate as much runoff as CN and TP, but more than CH (which had enhanced infiltration owing to its conductive macropores) during large storms.     

Persistence of glyphosate in a sandy loam

Glyphosale was added to samples of a sandy loam at rates of 0, 2, 5 and 10μg g^?1soil. After 120 days, soil was transferred to pots which were planted with subterranean clover. Plants were inoculated with Rhizohium trifolii and N₂ fixation (C₂H₂-reduction) was recorded after 9, 13, 15 and 19 weeks of growth. Nodule numbers and root weights were determined after the final C₂H₂-reduction assays had been performed. Decreased C₂H₂-reduction, nodule numbers and root weights associated with plants growing in glyphosate-treated soil indicated that this herbicide was not inactivated during the 120-days before planting.     

Relationships between microbial indices in roots and silt loam soils forming a gradient in soil organic matter

Perennial rye grass (Lolium perenne) was grown in a greenhouse pot experiment on seven soils to answer the question whether the microbial colonisation of roots is related to existing differences in soil microbial indices. The soils were similar in texture, but differed considerably in soil organic matter, microbial biomass, and microbial community structure. Ergosterol and fungal glucosamine were significantly interrelated in the root material. This ergosterol was also significantly correlated with the average ergosterol content of bulk and rhizosphere soil. In addition, the sum of fungal C and bacterial C in the root material revealed a significant linear relationship with microbial biomass C in soil. The colonisation of roots with microorganisms increased apparently with an increase in soil microbial biomass. In the root material, microbial tissue consisted of 77% fungi and 23% bacteria. In soil, the fungal dominance was slightly, but significantly lower, with 70% fungi and 30% bacteria. Fungal glucosamine in the root material was significantly correlated with that in soil (r=0.65). This indicates a close relationship between the composition of dead microbial remains in soil and the living fraction in soil and root material for unknown reasons.     

Influence of single passes with high wheel load on a structured, unploughed sandy loam soil

In a field experiment, a sandy loam was subjected to single passes with a sugar beet harvester at two different soil water potentials. Different hopper fillings resulted in ground contact pressures of 130 kPa (partial load) and 160 kPa (full load) underneath the tyre. Bulk density, macroporosity (equivalent pore radius >100 μm), penetrometer resistance, air permeability and pre-consolidation pressure were measured within and next to the wheel tracks at depths of 0.12–0.17, 0.32–0.37 and 0.52–0.57 m. Furthermore, the soil structure at two horizons (Ahp 7–24 cm, B(C) 24–38 cm) was visually assessed and classified.

The moist plot responded to a wheel load of 11.23 mg (160 kPa) with an increase in bulk density and pre-consolidation pressure as well as with a decrease in air permeability and macroporosity at a depth of 0.12–0.17 m. With a wheel load of 7.47 mg (130 kPa) on the moist plot and with both wheel load levels on the dry plot, only slight changes of the soil structure were detected. At a depth of 0.32–0.37 and 0.52–0.57 m, the measurements did not indicate any compaction. An ANOVA indicates that the factor “soil water potential” and the factor “wheel load” significantly influence the bulk density at a depth of 0.12–0.17 m. No interactions occurred between these two factors. The wheel traffic on the test plot had no effect on the yield of winter wheat planted after the experimental treatment.

Bulk density, macroporosity and pre-consolidation pressure proved to be sensitive to detect compaction because they varied only slightly and are easy to measure. In contrast, the standard deviation of air permeability is large. The soil structure determined visually in the field confirms the values measured in the laboratory. The results of the penetrometer resistance measurements were not explainable.     

Morphological and hydraulic properties of a silt loam soil in New Zealand as affected by cropping history

Abstract. A rotation trial of four years' pasture followed by two years' arable was used to study the effect of cropping on the morphological and hydraulic properties of soil. An adjacent paddock in grass for the past 35 years was included as a permanent pasture reference. Initial infiltration and field saturated hydraulic conductivity ( K _fs) were least for cultivated soil and increased with increasing time under pasture. This could be explained by the contrasting porosities of resin-impregnated blocks of undisturbed soil which had been infiltrated with methylene blue dye. Small K _fs values for cultivated soil resulted mainly from a thin surface crust, although pore discontinuity at the depth of the cultivation pan (130 mm) could also have contributed. Greater K _fs values under short-term pasture resulted primarily from water flowing through biogenic pores connected to the surface. The greatest K _fs values were in soil that had been under pasture for 35 years (P35). This was attributed to flow through biogenic pores and fissures associated with the strongly-developed subangular blocky structure. The amount of water that infiltrated the two- and four-year pasture soils (P2 and P4) under ponding was 2.5 and 5 times greater, respectively, than the soil that had been cultivated for two years (C2).
As irrigation duration cannot be varied under the border-dyking system used on the Canterbury Plains, the interval between irrigations must be varied if the same total amount of water is to be applied to each of these soils through the season. The interval should be less for the cultivated soil than for those under pasture, and should increase with increasing time under pasture (i.e. P35 > P4 > P2 > C2).     

Spring barley growth, grain quality and soil physical conditions in a cultivations experiment on a sandy loam in Scotland

Widely differing cultivations for spring barley, ranging from conventional ploughing to direct drilling and including broadcasting on to undisturbed soil, were examined over two seasons (1979 and 1980), conventional ploughing yielding highest and either chisel ploughing or direct drilling lowest. Yield differences were associated with plant population differences; they were significant only in the abnormally wet season of 1980. Broadcasting before tine cultivation to 50 mm resulted in lower seedbed strength and higher yield than drilling after a similar cultivation. Compaction by the same level of seedbed traffic was greater in a treatment cultivated to 50 mm depth than in the conventional ploughing treatment. Grain milling energy, which is inversely related to endosperm suitability for malting, and grain nitrogen content both decreased with increasing yield. Total nitrogen removed per ha in the grain in 1979 was similar in all treatments (about 72% of applied). In 1980, it was generally lower (about 62% of applied). After allowing for differences in plant populations it was lowest after direct drilling, broadcasting and very shallow tine cultivation (60% of applied), highest after conventional ploughing (70% of applied) and intermediate after rotary cultivating and shallow tine cultivation (65% of applied). Soil water release characteristics were described by logistic equations. Treatment differences were greatest at matric potentials greater than -3 kPa at 10 and 60 mm depth. The porosities of the cultivated soils were similar to each other, and were greater than those of the direct drilled treatments.     

Nitrogen uptake by ryegrass from organic wastes applied to a sandy loam soil

Sandy‐textured Mediterranean soils are invariably depleted in organic matter and supply only small amounts of N to crops. To compensate for these deficiencies, we tested the N supply from six organic wastes applied to a Cambic Arenosol in pots growing ryegrass. The results showed that the behaviour of the wastes in supplying N to a ryegrass crop grown in this soil can be predicted by observing their performance in laboratory aerobic incubations. The N made available during these incubations fitted well to a one‐pool kinetic model.