Effects of Selected Surfactants on Nutrient Uptake in Corn (Zea mays L.)

Surfactants in herbicide formulations eventually enter soil and may disrupt various processes. Research examined effects on nutrient uptake in corn caused by surfactants, herbicides, and surfactant-herbicide combinations applied to silt loam and silty clay loam soils in the greenhouse. Surfactants evaluated were Activator 90, Agri-Dex, and Thrust; herbicides were glyphosate, atrazine, and bentazon. Corn was planted in fertilized soils with moisture content maintained for optimum growth. Foliage (V8 growth stage) was collected for elemental analyses. Nutrient uptake differed with soil texture. Nutrient uptake from silty clay loam was more affected by surfactants and/or herbicides than in silt loam. Potassium uptake was significantly (P = 0.05) decreased in silt loam only by Thrust but uptake of phosphorus (P), potassium (K) calcium (Ca), sulfur (S), copper (Cu), and zinc (Zn) decreased by ≤30% in silty clay loam treated with surfactants. Surfactants and/or herbicides may interact with soil texture to affect nutrient uptake. Long-term field studies to validate changes in nutrient uptake and grain yields after annual applications of surfactants plus herbicides are needed.     

Effect of Select Surfactants on Activities of Soil Enzymes Involved in Nutrient Cycling

Experiments were conducted to investigate the impact of commonly used herbicides and surfactants on the activity of acid phosphatase, β-glucosidase, arylsulfatase, β-glucosaminidase, and dehydrogenase, using two soils (silt loam and silty clay loam) from Mid-Missouri, USA. The surfactants used in this study were alkylphenol ethoxylate + alcohol ethoxylate (ACTIVATOR 90), polyethoxylate (Agri-Dex®) and a blend of ammonium sulfate, drift reduction/deposition polymers, and an antifoam agent (THRUST®). The herbicides were glyphosate, atrazine, and bentazon. Surfactants and herbicides were applied to soils at the label rate, either alone or combined. In general, enzyme activity was enhanced more in silt loam soil than in silty clay loam soil. Acid phosphatase displayed the greatest amount of enzymatic activity within soils; dehydrogenase displayed the most inhibition, whilst β-glucosidase and β-glucosaminidase fluctuated based on treatment. ACTIVATOR 90 appeared to have the most inhibitory effect on enzymatic activity within soils compared to the control.     

Soil texture affects soil microbial and structural recovery during grassland restoration

Many biotic and abiotic factors influence recovery of soil communities following prolonged disturbance. We investigated the role of soil texture in the recovery of soil microbial community structure and changes in microbial stress, as indexed by phospholipid fatty acid (PLFA) profiles, using two chronosequences of grasslands restored from 0 to 19 years on silty clay loam and loamy fine sand soils in Nebraska, USA. All restorations were formerly cultivated fields seeded to native warm-season grasses through the USDA’s Conservation Reserve Program. Increases in many PLFA concentrations occurred across the silty clay loam chronosequence including total PLFA biomass, richness, fungi, arbuscular mycorrhizal fungi, Gram-positive bacteria, Gram-negative bacteria, and actinomycetes. Ratios of saturated:monounsaturated and iso:anteiso PLFAs decreased across the silty clay loam chronosequence indicating reduction in nutrient stress of the microbial community as grassland established. Multivariate analysis of entire PLFA profiles across the silty clay loam chronosequence showed recovery of microbial community structure on the trajectory toward native prairie. Conversely, no microbial groups exhibited a directional change across the loamy fine sand chronosequence. Changes in soil structure were also only observed across the silty clay loam chronosequence. Aggregate mean weighted diameter (MWD) exhibited an exponential rise to maximum resulting from an exponential rise to maximum in the proportion of large macroaggregates (>2000 μm) and exponential decay in microaggregates (<250 μm and >53 μm) and the silt and clay fraction (<53 μm). Across both chronosequences, MWD was highly correlated with total PLFA biomass and the biomass of many microbial groups. Strong correlations between many PLFA groups and the MWD of aggregates underscore the interdependence between the recovery of soil microbial communities and soil structure that may explain more variation than time for some soils (i.e., loamy fine sand). This study demonstrates that soil microbial responses to grassland restoration are modulated by soil texture with implications for estimating the true capacity of restoration efforts to rehabilitate ecosystem functions.     

Extractability of 2,4-D,Dicamba and MCPP from Soil

The adsorption of herbicides on soil colloids is a major factor determining their mobility, persistence, and activity in soils. Solvent extraction could be a viable option for removing sorbed contaminants in soils. This study evaluated the extractability of three herbicides: 2,4 dichlorophenoxy-acetic acid (2,4-D), 4-chloro-2-methylphenoxypropanoic acid (mecoprop acid or MCPP), and 3,6-dichloro-2-methoxybenzoic acid (dicamba). Three solvents (water, methanol, and iso-propanol) and three methods of extraction (column, batch, and soxhlet) were compared for their efficiencies in removing the herbicides from three soils (loamy sand, silt loam, and silty clay). Both linear and non-linear Freundlich isotherms were used to predict sorption intensity of herbicides on soils subjected to various extraction methods and conditions. High K_dand K_fr, and low N values were obtained for all herbicides in silty clay soil by batch extraction. Methanol was the best solvent removing approximately 97% of all added herbicides from the loamy sand either by column or soxhlet extraction method. Isopropanol ranked second by removing over 90% of all herbicides by soxhelet extraction from all three soils. However, water was ineffective in removing herbicides from any of the soils using any of the three extracting procedures used in this study. In general, the extent of herbicide removal depended on soil type, herbicide concentration, extraction procedure, solvent type and amount, and extraction time.     

The influence of soil and biosolids type,and microbial immobilisation on nitrogen availability in biosolids‐amended agricultural soils – implications for fertiliser recommendations

Soil microbial biomass interactions influencing the mineralisation of N in biosolids‐amended agricultural soil were investigated under field conditions in two soil types, a silty clay and a sandy silt loam, with contrasting organic matter contents. Soil treatments included: dewatered raw sludge (DRAW); dewatered and thermally dried, mesophilic anaerobically digested biosolids (DMAD and TDMAD, respectively); lime‐treated unstabilised sludge cake (LC); and NH₄Cl as a mineral salt control for measuring nitrification kinetics. Soil mineral N and microbial biomass N (MBN) concentrations were determined over 90 days following soil amendment. Despite its lower total and mineral N contents, TDMAD had a larger mineralisable pool of N than DMAD, and was an effective rapid release N source. Increased rates of mineralisation and nitrification of biosolids‐N were observed in the silty clay soil with larger organic matter content, implying increased microbial turnover of N in this soil type compared with the sandy silt loam, but no significant difference in microbial immobilisation of biosolids‐N was observed between the two soil types. Thus, despite initial differences observed in the rates of N mineralisation, the overall extent of N release for the different biosolids tested was similar in both soil types. Therefore, the results suggest that fertiliser guidelines probably do not need to consider the effect of soil type on the release of mineral N for crop uptake from different biosolids products applied to temperate agricultural soils.     

美国堪萨斯州不同天气事件与土壤类型条件下作物产量预测

Computer simulation was used for predictive analysis of the effects of weather and soil type on crop yield in the U.S.crop insurance program.The Environmental Policy Integrated Climate (EPIC) model was modified to include hail weather events,which completed the modifications necessary to simulate the four most frequent causes of crop yield loss (hail,excessive wet,excessive cold,and excessive dry) associated with soil type in Kansas,USA.At the region level,per hectare yields were simulated for corn,wheat,soybean,and sorghum.We concluded that it was possible to predict crop yields through computer simulation with greater than 93% accuracy.The hail damage model test indicated EPIC could predict hail-soil-induced yield losses reasonably well (R² > 0.6).The investigation of soil type influence on dryland sorghum and wheat production indicated that Wymore silty clay loam soil and Kenoma silt loam produced the highest sorghum yields statistically;Kuma silt loam,Roxbury silt loam,Crete silty clay loam,and Woodson silt soils produced the second highest sorghum yields statistically;and Richfiled silt loam,Wells loam,and Canadian sandy loam produced the lowest sorghum yields.By contrast,wheat production showed less sensitivity to soil type variation.The less sensitive response of wheat yields to the soil type could be largely due to the unconsidered small-scale variability of soil features.     

Data transformations between soil texture schemes

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

Changes in microbial community structure following herbicide (glyphosate) additions to forest soils

Glyphosate applied at the recommended field rate to a clay loam and a sandy loam forest soil resulted in few changes in microbial community structure. Total and culturable bacteria, fungal hyphal length, bacterial:fungal biomass, carbon utilization profiles (BIOLOG), and bacterial and fungal phospholipid fatty acids (PLFA) were unaffected 1, 3, 7, or 30 days after application of a commercial formulation (Roundup^®). In contrast, a high concentration of glyphosate (100× field rate) simulating an undiluted chemical spill substantially altered the bacterial community in both soils. Increases in total bacteria, culturable bacteria, and bacterial:fungal biomass were rapid following application. Culturable bacteria increased from about 1% of the total population in untreated soil to as much as 25% at the high concentration by day 7, indicating enrichment of generalist bacteria. Community composition in both soils shifted from fungal dominance to an equal ratio of bacteria to fungi. Functional diversity of culturable bacteria, estimated by C substrate utilization, also increased at the high glyphosate concentration, particularly in the clay loam soil. Unlike the other bacterial indices, only minor changes in bacterial PLFA resulted after the third day following the 100× field rate application. Apparently the herbicide resulted in an across-the-board stimulation of bacteria that was not reflected by the finer-scale PLFA community structure. Changes in fungal properties (hyphae, propagules, PLFA biomarkers) were few and transient. We conclude that the commercial formulation of glyphosate has a benign affect on community structure when applied at the recommended field rate, and produces a non-specific, short-term stimulation of bacteria at a high concentration.     

Soil carbon responses to past and future CO2 in three Texas prairie soils

Changes in soil carbon storage could affect and be affected by rising atmospheric CO₂. However, it is unlikely that soils will respond uniformly, as some soils are more sensitive to changes in the amount and chemistry of plant tissue inputs whereas others are less sensitive because of mineralogical, textural, or microbial processes. We studied soil carbon and microbial responses to a preindustrial-to-future CO₂ gradient (250–500 ppm) in a grassland ecosystem in the field. The ecosystem contains three soil types with clay fractions of 15%–55%: a sandy loam Alfisol, a silty clay Mollisol, and a black clay Vertisol. Soil and microbial responses to atmospheric CO₂ are plant-mediated; and aboveground plant productivity in this ecosystem increased linearly with CO₂ in the sandy loam and silty clay. Although total soil organic carbon (SOC) did not change with CO₂ treatment after four growing seasons, fast-cycling SOC pools increased with CO₂ in the two clay soils. Microbial biomass increased 18% and microbial activity increased 30% across the CO₂ gradient in the black clay (55% clay), but neither factor changed with CO₂ in the sandy loam (15% clay). Similarly, size fractionation of SOC showed that coarse POM-C, the youngest and most labile fraction, increased four-fold across the CO₂ gradient in the black clay, but increased by only 50% across the gradient in the sandy loam. Interestingly, mineral-associated C, the oldest and most recalcitrant fraction, declined 23% across the gradient in the third soil type, a silty clay (45% clay). Our results provide evidence for priming in this soil type, as labile C availability and decomposition rate (measured as soil respiration and soil C mineralization) also increased across the CO₂ gradient in the silty clay soil. In summary, CO₂ enrichment in this grassland increased the fast-cycling SOC pool as in other CO₂ studies, but only in the two high-clay soils. Priming in the silty clay could limit SOC accumulation after prolonged CO₂ exposure. Because soil texture varies geographically, including data on soil types could enhance predictions of soil carbon and microbial responses to future CO₂ levels.     

Fate of diuron and terbuthylazine in soils amended with two-phase olive oil mill waste

The addition of organic amendments to soil increases soil organic matter content and stimulates soil microbial activity. Thus, processes affecting herbicide fate in the soil should be affected. The objective of this work was to investigate the effect of olive oil production industry organic waste (alperujo) on soil sorption-desorption, degradation, and leaching of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and terbuthylazine [N2-tert-butyl-6-chloro-N4-ethyl-1,3,5-triazine-2,4-diamine], two herbicides widely used in olive crops. The soils used in this study were a sandy soil and a silty clay soil from two different olive groves. The sandy soil was amended in the laboratory with fresh (uncomposted) alperujo at the rate of 10% w/w, and the silty clay soil was amended in the field with fresh alperujo at the rate of 256 kg per tree during 4 years and in the laboratory with fresh or composted alperujo. Sorption of both herbicides increased in laboratory-amended soils as compared to unamended or field-amended soils, and this process was less reversible in laboratory-amended soils, except for diuron in amended sandy soil. Addition of alperujo to soils increased half-lives of the herbicides in most of the soils. Diuron and terbuthylazine leached through unamended sandy soil, but no herbicide was detected in laboratory-amended soil. Diuron did not leach through amended or unamended silty clay soil, whereas small amounts of terbuthylazine were detected in leachates from unamended soil. Despite their higher sorption capacity, greater amounts of terbuthylazine were found in the leachates from amended silty clay soils. The amounts of dissolved organic matter from alperujo and the degree of humification can affect sorption, degradation, and leaching of these two classes of herbicides in soils. It appears that adding alperujo to soil would not have adverse impacts on the behavior of herbicides in olive production.     

外源铬对小白菜(Brassica chinensis L.)根际土壤微生物生物量和磷脂脂肪酸的剖面分布特征的影响

The effects of root activity on microbial response to cadmium （Cd） loading in the rhizosphere are not well understood. A pot experiment in greenhouse was conducted to investigate the effects of low Cd loading and root activity on microbial biomass and community structure in the rhizosphere of pakchoi （Brassica chinensis L.） on silty clay loam and silt loamy soil. Cd was added into soil as Cd（NO3）2 to reach concentrations ranging from 0.00 to 7.00 mg kg-1. The microbial biomass carbon （MBC） and community structure were affected by Cd concentration, root activity, and soil type. Lower Cd loading rates （〈 1.00 mg kg-1） stimulated the growth of pakchoi and microorganisms, but higher Cd concentrations inhibited the growth of microorganisms. The content of phospholipid fatty acids （PLFAs） was sensitive to increased Cd levels. MBC was linearly correlated with the total PLFAs. The content of general PLFAs in the fungi was positively correlated with the available Cd in the soil, whereas those in the bacteria and actinomycetes were negatively correlated with the available Cd in the soil. These results indicated that fungi were more resistant to Cd stress than bacteria or actinomycetes, and the latter was the most sensitive to Cd stress. Microbial biomass was more abundant in the rhizosphere than in the bulk soil. Root activity enhanced the growth of microorganisms and stabilized the microbial community structure in the rhizosphere. PLFA analysis was proven to be sensitive in detecting changes in the soil microbial community in response to Cd stress and root activity.     

Does biochar interfere with standard methods for determining soil microbial biomass and phenotypic community structure?

Due to its high sorption affinity for organic compounds, biochar may interfere with extraction procedures involving such compounds used for microbially-related assays commonly applied to soils. Here we assessed the impact of two biochars (derived from pine bark and produced at 300 and 600 °C) at three concentrations (0, 12.5, and 50 g kg⁻¹) in three distinct arable soils with contrasting textural classes (loamy sand, sandy loam, and clay) on the determination of soil microbial biomass C by fumigation–extraction, fungal biomass by ergosterol analysis, and microbial community structure as defined by phospholipid fatty acid (PLFA) profiling. Biochar did not affect the apparent concentration of soil microbial biomass C and had no significant impact on apparent PLFA profiles. By contrast, the apparent extraction efficiency of ergosterol was affected dependent on soil type, biochar production temperature, and biochar concentration. Nonetheless, ergosterol contents of biochar-amended soils can be accurately estimated by correcting for reduced recovery using an ergosterol spike.     

Effect of Continuous Rice–Wheat Rotation on Soil Properties from Four Agro‐ecosystems of Indian Punjab

In Indian Punjab, rice–wheat is a dominant cropping system in four agro‐ecosystems, namely undulating subregion (zone 1), Piedmont alluvial plains (zone 2), central alluvial plains (zone 3), and southwestern alluvial plains (zone 4), varying in rainfall and temperature. Static and temporal variabilities in soil physical and chemical properties prevail because of alluvial parent material, management/tillage operations, and duration of rice–wheat rotation. A detailed survey was undertaken to study the long‐term effect of rice–wheat rotation on soil physical (soil separates, bulk density, modulus of rupture, saturated and unsaturated hydraulic conductivities, soil water content, and suction relations) and chemical (organic carbon, pH, electrical conductivity) properties of different textured soils (sandy clay loam, loam, clay loam, and silty clay loam) in these four zones of Punjab. Soil samples (of 0‐ to 30‐cm depth) from 45 sites were collected during 2006 and were analyzed for physical and chemical properties. The results showed that sand content and pH increased whereas silt and organic carbon decreased significantly from zones 1 to 4. Compared to other textures, significantly greater organic carbon, modulus of rupture, and pH in silty clay loam; greater bulk density in clay loam, and greater saturated hydraulic conductivity in sandy clay loam were observed. Irrespective of zone and soil texture, in the subsurface soil, there was a hard pan at 15–22.5 cm deep, which had high soil bulk density, modulus of rupture, more silt and clay contents (by 3–5%) and less organic carbon and hydraulic conductivity than the surface (0–15 cm) layer. These properties deteriorated with fineness of the soil texture and less organic carbon content. Continuous rice–wheat cropping had a deleterious effect on many soil properties. Many of these soils would benefit from the addition of organic matter, and crop yields may also be affected by the distinct hardpan that exists between 15 and 22.5 cm deep.     

Organic carbon mineralization responses to temperature increases in subtropical paddy soils

Purpose

Understanding organic carbon mineralization and its temperature response in subtropical paddy soils is important for the regional carbon balance. There is a growing interest in factors controlling soil organic carbon (SOC) mineralization because of the potential for climate change. This study aims to test the hypothesis that soil clay content impedes SOC mineralization in subtropical paddy soils.

Materials and methods

A 160-day laboratory incubation at temperatures from 10 to 30 °C and 90% water content was conducted to examine the dynamics of SOC mineralization and its temperature response in three subtropical paddy soils with different clay contents (sandy loam, clay loam, and silty clay soils). A three-pool SOC model (active, slow, and resistant) was used to fit SOC mineralization.

Results and discussion

Total CO₂ evolved during incubation following the order of clay loam > silty clay > sandy loam. The temperature response coefficients (Q ₁₀) were 1.92?±?0.39, 2.36?±?0.22, and 2.10?±?0.70, respectively, for the sandy loam soil, clay loam soil, and silty clay soil. But the soil clay content followed the order of silty clay > clay loam > sandy loam. The sandy loam soil neither released larger amounts of CO₂ nor showed higher temperature sensitivity, as expected, even though it contains lower soil clay content among the three soils. It seems that soil clay content did not have a dominant effect which results in the difference in SOC mineralization and its temperature response in the selected three paddy soils. However, dissolved organic carbon (DOC; representing substrate availability) had a great effect. The size of the active C pool ranged from 0.11 to 3.55% of initial SOC, and it increased with increasing temperature. The silty clay soil had the smallest active C pool (1.40%) and the largest Q ₁₀ value (6.33) in the active C pool as compared with the other two soils. The mineralizable SOC protected in the silty clay soil, therefore, had even greater temperature sensitivity than the other two soils that had less SOC stabilization.

Conclusions

Our study suggests that SOC mineralization and its temperature response in subtropical paddy soils were probably not dominantly controlled by soil clay content, but the substrate availability (represented as DOC) and the specific stabilization mechanisms of SOC may have great effects.     

Effect of some herbicides on microbial activity in soil

The effect of 25 herbicides and herbicide combinations, in amounts comparable to those used in agriculture, on microbial activity in two soil types was determined in the laboratory. Herbicides did not affect respiration, assayed by CO₂ evolution and dehydrogenase activity, in either silty clay loam or loamy sand. Organic matter decomposition, determined by the amount of CO₂ evolved and inorganic N formed from decomposing alfalfa tissue, was also not affected. Alteration in soil pH or moisture content did not affect herbicide action. Addition of herbicides 3 weeks before amendment, or fertilizer application, also did not influence herbicide activity. Selected herbicides (trifluralin, linuron, dinoseb) at concentrations 100-fold higher than the recommended rates did not affect alfalfa decomposition. Solubilization of Ca₃(PO₄)₂ in soil was not affected by herbicides. S oxidation to SO^2?₄ in soil, however, was increased by most herbicides. In silty clay loam, 18 of the 25 herbicides and herbicide combinations increased S oxidation almost up to 3-fold. Results in loamy sand were similar. Dinoseb effectively reduced the algal population in loamy sand by more than 90%. Trifluralin, linuron, and metribuzin did not inhibit algal populations.     

Sorption-desorption of "aged" sulfonylaminocarbonyltriazolinone herbicides in soil

Sorption-desorption interactions of pesticides with soil determine the availability of pesticides in soil for transport, plant uptake, and microbial degradation. These interactions are affected by the physical and chemical properties of the pesticide and soil, and for some pesticides, their residence time in the soil. The objective of this study was to characterize sorption-desorption of two sulfonylaminocarbonyltriazolinone herbicides incubated in soils at different soil moisture potentials. The chemicals were incubated in clay loam and loamy sand soils for up to 12 wks at -33 kPa and at water contents equivalent to 50 and 75% of that at -33 kPa. Chemicals were extracted sequentially with 0.01 N CaCl(2) and aqueous acetonitrile, and sorption coefficients were calculated. Sufficient sulfonylaminocarbonyltriazolinone herbicides remained (>40% of that applied) during incubation to allow calculation of sorption coefficients. Aging significantly increased sorption as indicated by increased sorption coefficients. For instance, for sulfonylaminocarbonyltriazolinone remaining after a 12-wk incubation at -33 kPa, K(d) increased by a factor of 4.5 in the clay loam soils and by 6.6 in the loamy sand as compared to freshly treated soils. There was no effect of moisture potential on sorption K(d) values. These data show the importance of characterization of sorption-desorption in aged herbicide residues in soil, particularly in the case of prediction of herbicide transport in soil. In this case, potential transport of sulfonylaminocarbonyltriazolinone herbicides would be over-predicted if freshly treated soil K(d) values were used to predict transport.     

Carbon and net nitrogen mineralisation in two forest soils amended with different concentrations of biuret

Biuret is a known contaminant of urea fertilisers that might be useful as a slow release N fertiliser for forestry. We studied carbon (C), net nitrogen (N) mineralisation and soil microbial biomass C and N dynamics in two forest soils (a sandy loam and a silt loam) during a 16-week long incubation following application of biuret (C 23.3%, N 40.8%, O 30.0% and H 4.9%) at concentrations of 0, 2, 10, 100 and 1000 mg kg⁻¹ (oven-dried) soil to assess the potential of biuret as a slow-release N fertiliser. Lower concentrations of biuret specifically increased C mineralisation and soil microbial biomass C in the sandy loam soil, but not in the silt loam soil. A significant decrease of microbial biomass C was found in both soils at week 16 after biuret was applied at higher concentrations. C mineralisation declined with duration of incubation in both soils due to decreased C availability. Biuret at concentrations from 10 to 100 mg kg⁻¹ soil had a significantly positive priming effect on soil organic N mineralisation in both soils. The causes for the priming effects were related to the stimulation of microbial growth and activity at an early stage of the incubation and/or the death of microbes at a later stage, which was biuret-concentration-dependent. The patterns in NH₄⁺-N accumulation differed markedly between the two soils. Net N mineralisation and nitrification were much greater in the sandy loam soil than in the silt loam soil. However, the onset of net nitrification was earlier in the silt loam soil. Biuret might be a potential slow-release N source in the silt loam soil.     

Erosion processes and erodibility of cultivated soils in North Rhine‐Westphalia under artificial rain. II. Results of field experiments and comparison with laboratory trials

In the densely populated state of North Rhine‐Westphalia, soil erosion by water causes substantial on‐site degradation and off‐site damages. The implementation of soil‐conservation measures is improved, if soil erodibilities and erosion processes are known. In a state‐wide investigation, we aimed to representatively assess soil‐erosion processes and erodibilities of cultivated soils. For this purpose, we measured surface runoff and soil‐loss rates of 28 cultivated soils with field plots under artificial rain. In the field experiments, surface runoff and soil loss indicated high sealing susceptibilities and high erodibilities on soils of quite different textures including a clay silt, a loam silt, a loam sand, a sand loam, and two standard loams. Rill formation causing high soil‐loss rates was observed on a clay silt (soil BM) and on a loam silt (soil RB), the latter yielding an empirical K‐factor of 1.66 t ha^–1 h N^–1. K‐factors of other silty soils ranged from 0.04 to 0.48, whereas sandy soils and clayey soils had K‐factors ranging from 0.00 to 0.32, and 0.00 to 0.12, respectively. Comparatively high erodibilities of two silt clays were due to saturation overland flow. Erosion processes and erodibilities of soils with similar texture varied to a large extent, possibly caused in part by seasonal differences in the timing of erosion tests. Surface runoff was different in field experiments compared with laboratory experiments (companion paper) conducted with topsoil material taken from the field plots. In addition, higher concentrations of suspended sediment were recorded on average in the field than in the laboratory. These differences might reflect the influence of the subsoil and are due to higher transport capacities on longer plots in the field. Thus, laboratory experiments can complement but not replace costly field trials for K‐factor determination. Empirical K‐factors derived from field and laboratory experiments are in general lower than K‐factors of other soils in Germany or calculated K‐factors derived from pedotransfer functions, which might be attributed to a more maritime‐type climate in North Rhine‐Westphalia. Since the temporal variability of erodibility was not assessed, the reported K‐factors should be regarded as preliminary.     

江淮流域白浆化土壤的矿物组成与化学特性的研究

对采自江淮流域的7个典型白浆化工土壤剖面不同粒级的矿物特性与化学组成进行了研究。结果表明：该区域白浆化土壤的质地为粉砂质壤土及粘壤土，粉粒含量为45%～76%。粘粒矿物以水云母为主，含量为60%～80%，继承了黄土母质的特性，土体硅铝率（Sa)与硅铁铝率（Saf）分别为7.70～14.05与6.43～10.24，而粘粒的分别为3.53～4.22和2.40～3.35。各剖面土体Sa与Saf以表层较高或最高，有明显富硅现象；而粘粒的Sa和Saf及矿物组成，颗粒组成的层次差异则表现出母质层次上的不连续性，白土层与粘化层的显著分异是由于全新世黄土性沉积物，经过冲积淤积交替更迭，加上后期淋溶淀积而成；脱硅、脱盐基和富铝化及氧化还原淋溶淀积是其重要成土过程，后一过程不同的利用方式，强度有所差别，以水稻土较强。     

Influence of texture on habitable pore space and bacterial-protozoan populations in soil

Summary Soil texture affects pore space, and bacterial and protozoan populations in soil. In the present study we tested the hypothesis that bacteria are more protected from protozoan predation in fine-textured soils than in coarse-textured soils because they have a larger volume of protected pore space available to them. The experiment consisted of three sterilized Orthic Black Chernozemic soils (silty clay, clay loam, and sandy loam) inoculated with bacteria, two treatments (with and without protozoa), and five sampling dates. The soils were amended with glucose and mineral N on day 0. On day 4 bacterial numbers in all three soils were approximately 3×10⁹ g^–1 soil. The greatest reduction in bacteria due to protozoan grazing occurred between day 4 and day 7. Compared to the treatment without protozoa, bacteria in the treatment with protozoa were reduced by 68, 50, and 75% in the silty clay, clay loam, and sandy loam, respectively. On day 4, 2 days after the protozoan inoculation, all protozoa were active. The numbers were 10330, 4760, and 15 380 g^–1 soil for the silty clay, clay loam, and sandy loam, respectively. Between day 4 and day 7, the period of greatest bacterial decline, total protozoa increased greatly to 150480, 96160, and 192100 g^–1 soil for the three soils, respectively. Most protozoa encysted by day 7. In all soils the addition of protozoa significantly increased CO₂–C evolution per g soil relative to the treatment without protozoa. Our results support the hypothesis that bacteria are more protected from protozoan predation in fine-textured soils than in coarse-textured soils.