Specific draught for mouldboard plough, chisel plough and disc harrow at different water contents

The objective of the present study was to measure the specific draught (force per cross-sectional area of worked soil) and energy use for soil fragmentation for different tillage implements and soil conditions. Draught was calculated from measurements of fuel consumption and speed during tillage with a mouldboard plough and a chisel plough set to working depths of 13, 17 and 21 cm, and a disc harrow. Tillage was carried out at three different water contents (“Wet”, “Moist” and “Dry”) on two sites. The average working depth was calculated from weighing the loose soil within a 0.25-m² frame. Specific area of the soil was determined by sieving. Soil strength was measured in situ using a shear vane and a penetrometer. Average working depth was much less than the set working depth for the chisel plough. Specific draught was generally the lowest for the mouldboard plough and the highest for the chisel plough, and increased with decreasing soil water content. The specific draught was strongly correlated to soil cohesion, but not to penetration resistance. The proportion of coarse aggregates after tillage was the highest for the mouldboard plough and the lowest for the moist soil. The energy use for soil fragmentation was in most cases the lowest for the disc harrow, while there were small differences between the chisel and the mouldboard ploughs. The results show that the mouldboard plough is energy efficient for loosening soil, while the disc harrow is energy efficient for soil fragmentation during primary tillage. Tillage at an intermediate water content, close to the plastic limit, gave the largest proportion of small aggregates and consequently the lowest energy use for soil fragmentation.     

Influence of tool angles and speed on the soil reactions of a bent leg plough in two soils

The soil reactions of bent leg ploughs, as influenced by tool angles, need to be studied in detail in order to optimise their performance under different soil and operational conditions. In a field study conducted at Kumulur, south India, three bent leg tool models, with 30°, 37.5° and 45° bend angles, were tested for their soil reactions in a Typic Ustocrept (loamy sand) and a Typic Chromustert (clay loam) soil, under different speeds of operation and rake angles. A simple and reliable instrumentation system, capable of measuring the soil reactions of the tools, was developed and used in this study. Mathematical response models were built on these soil reactions to optimise the parametric levels yielding maximum performance. It was found that the tool, while working in the Ustocrept (loamy sand) and Chromustert (clay loam) soils, should have a rake angle between 9° and 15° for minimum horizontal and lateral soil reactions, and maximum downward suction, aiding penetration.     

Time-dependent sorption of imidacloprid in two different soils

Time-dependent sorption of imidacloprid [1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine] was investigated with two German soils (sandy loam and silt loam). Soil batches containing the active ingredient (0.33 mg/kg) were incubated for 100 days. After selected aging periods, imidacloprid desorbed by 0.01 M CaCl(2) (soluble phase) and by organic solvents (methanol and acetonitrile) and reflux extraction with acidified methanol (sorbed phase) was determined. Calculated sorption coefficients K(d) and K(oc) increased by a factor of 3.2-3.8 during 100 days of aging. Additionally, the time-dependent sorption was verified by a column leaching experiment with the aged soil. The amount of imidacloprid in column eluates (0.01 M CaCl(2)) decreased compared to total recovered by a factor of approximately 2. Sorption of imidacloprid thus increased with residence time in soil, making it more resistant to leaching. These results are further information to explain the low leaching potential of imidacloprid in the field, despite its high water solubility.     

Erodibility of model soils with different densities

Soil erodibility as a function of the soil density was studied in a hydraulic flume. The experiments were performed with mixtures of aggregates and different-sized chernozemic soil particles with the predominance of the fraction of 0.5–2 mm, which corresponded to their proportions in the plow horizon. It was found that, when the soil density increased, the erodibility abruptly decreased and was well described by a power function with an exponent of −9.25 (R ² = 0.997). The approximate calculation of the contact area between the aggregates showed that the cohesion force between them is not a linear function of the total area of the interaggregate contacts.     

Temporal denitrification patterns in different horizons of two riparian soils

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

Recolonization of methyl bromide sterilized soils under four different field conditions

Summary The course of recovery in biological activity was assessed in the top 5 cm of undisturbed soil cores (29.7 cm diameter, 30 cm deep) that had been fumigated in the laboratory with methyl bromide. The cores were returned to their original pasture and forest sites, two with a moderate and two with a high rainfall, and untreated soils at all sites served as baselines. Sampling took place over 166 days (midsummer to midwinter). Microbial biomass (as measured by fumigation-extraction and substrate-induced respiration procedures) and dehydrogenase activity both recovered rapidly, but remained consistently lower in the fumigated than in untreated samples at both forest sites and at the moister of the two pasture sites. Bacterial numbers also recovered rapidly. Fungal hyphal lengths were, on average over 166 days, 25% lower in the fumigated soils. Levels of mineral N were initially highest in the fumigated soils, but declined with time. Fumigation generally had no detectable effects on the subsequent rates of net N mineralization and little effect on nitrification rates. Fumigation almost totally eliminated protozoa, with one to three species being recovered on day 0; the numbers recovered most rapidly in the moist forest soil and slowly in the dry pasture soil. The recoionization rate of protozoan species was similar in all soils, with species numbers on day 110 being 33 and 34 in the fumigated and untreated soils, respectively. Nematodes were eliminated by fumigation; recolonization was first detected on day 26 but by day 166, nematode numbers were still lower in fumigated than in untreated soils, the abundance being 10 and 62 g^-1 soil and diversity 10 and 31 species, respectively. Overall, the results suggest that protozoan and nematode populations and diversities could provide a useful medium-term ecological index of the recovery in comprehensive soil biological activity following major soil pollution or disturbance.     

Nitrification in two coniferous forest soils after different fertilization treatments

The effects of seven different fertilization treatments on nitrification in the organic horizons of a Myrtillus-type (MT) and a Calluna-type pine forest in southern Finland were studied. No (NO^?₃ + NO^?₂)-N accumulated in unfertilized soils during 6 weeks at 14 or 20°C in the laboratory. Net nitrification was stimulated by urea in both soils (but more in the MT pine forest soil) and to a lesser degree by wood ash but not by ammonium nitrate or nitroform (ureaformaldehyde). Nitrification was not detected in nitroform fertilized soils although ammonium accumulation was high during incubation. In the MT pine forest soil, net nitrification appeared to be stimulated by apatite, biotite and micronutrients. Nitrapyrin inhibited nitrification indicating that it was carried out by autotrophic nitrifiers. In the urea-fertilized MT pine forest soil, nitrification took place at an incubation temperature of 0°C. Accumulation of (N0^?₃ + NO^?₂)-N was highest in soil sampled at < 10°C.     

Incorporation of urea-derived 13C into microbial communities in four different agriculture soils

The objective of this study was to investigate changes in the composition of the soil microbial community brought about by urea application and differences in the incorporation of urea-derived C into the soil phospholipid fatty acid (PLFA) pool at differing soil pH. We selected four soils which ranged in pH from 3.9 to 7.8. ¹³C-labeled urea was applied at two concentrations 100 and 200 mg N kg^?1 which represents commonly used and high levels of application. Significant hydrolysis of applied urea occurred within 2 h; less than 2 % of urea-C was retained in the soil with one exception, the fluvo-aquic soil at pH 7.8 amended with 200 mg kg^?1 urea-N 3 days after urea application. According to principal component analysis (PCA), the effect of urea and incubation time on microbial community composition was far weaker than differences between the four soils due to their large differences in basic properties; the scores of PC2 were significantly correlated with pH values. The incorporation of ¹³C-urea to PLFAs increased with soil pH; this may be related to increases in the speciation of inorganic C into bicarbonate.¹³C label was primarily incorporated into 16:1ω5c, 16:0, and cy19:0 in red soil, pH 3.9; and into 16:1ω7c, 16:0, and 16:1ω5c in fluvo-aquic soil, pH 7.8. A wider range of PLFAs became labeled in the two paddy soils at pH 5.2 and 6.7. This suggests that the profile of PLFAs labeled from the application of ¹³C-urea may be affected by redox potential.     

Suitability of a hydraulic‐conductivity model for predicting salt effects on swelling soils

Many empirical approaches have been developed to analyze changes in hydraulic conductivity due to concentration and composition of equilibrium solution. However, in swelling soils these approaches fail to perform satisfactorily, mainly due to the complex nature of clay minerals and soil–water interactions. The present study describes the changes in hydraulic conductivity of clay (Typic Haplustert) and clay‐loam (Vertic Haplustept) soils with change in electrolyte concentration (TEC) and sodium‐adsorption ratio (SAR) of equilibrium solution and assesses the suitability of a model developed by Russo and Bresler (1977) to describe the effects of mixed Na‐Ca‐Mg solutions on hydraulic conductivity. Four solutions encompassing two TEC levels viz., 5 and 50 mmol_c L^–1 and two SAR levels viz., 2.5 and 30 mmol^1/2 L^–1/2 were synthesized to equilibrate the soil samples using pure chloride salts of Ca, Mg, and Na at Ca : Mg = 2:1. Diluting 50 mmol_c L^–1 solution to 5 mmol_c L^–1 reduced saturated hydraulic conductivity of both soils by 66%, and increasing SAR from 2.5 to 30 mmol^1/2 L^–1/2 decreased saturated hydraulic conductivity by 82% and 79% in clay and clay‐loam soils, respectively. Near saturation, the magnitude of the change in unsaturated hydraulic conductivity due to the change in TEC and SAR was of 10³‐ and 10²‐fold, and at volumetric water content of 0.20 cm³ cm^–3, it was of 10¹⁴‐ and 10⁶‐fold in clay and clay‐loam soils, respectively. Differences between experimental and predicted values of saturated hydraulic conductivity ranged between 0.6% and 11% in clay and between 0.06% and 2.1% in clay‐loam soils. Difference between experimental and predicted values of unsaturated hydraulic conductivity widened with drying in both soils. Predicted values were in good agreement with the experimental values of hydraulic conductivity in clay and clay‐loam soils with R² values of 0.98 and 0.94, respectively. The model can be satisfactorily used to describe salt effects on hydraulic conductivity of swelling soils in arid and semiarid areas, where groundwater quality is poor.     

The role of clay, organic carbon and long-term management on mouldboard plough draught measured on the Broadbalk wheat experiment at Rothamsted

Despite a high energy requirement, the mouldboard plough remains the dominant tillage tool in northwest Europe. The aim of this work was to evaluate the relative influences of soil texture (clay content), soil organic carbon (SOC) and long‐term management on soil‐specific draught (S), where S is the force per cross‐sectional area of worked soil. Measurements were made during autumn 2000 on the then 157‐year‐old Broadbalk wheat experiment at Rothamsted, UK, where clay contents vary from 19 to 39% and the different cropping history, mineral and organic fertilizer treatments lead to SOC values of 0.7–3.2%. Minimum SOC values increased with increasing clay and were associated with zero or low mineral N inputs, while higher SOC values (>2%) were associated with long‐term applications of farmyard manure (FYM), despite these being on the lighter (<24% clay) soils. S values ranged between 52 and 142 kPa, with higher values co‐located in areas with high clay contents. Contour maps were generated to illustrate the spatial variability of S and show similarity to those for clay. Where FYM had been added, S was 66 kPa compared with 74 kPa where only mineral or no fertilizer was applied on soils of the same texture. Increasing applications of mineral N resulted in relatively small increases in SOC but up to 12% reduction in S.     

A model for predicting the fate of nitrogen fertilizer in lowland ricefields

Equations are developed for the simultaneous movement and reaction in flooded soils of urea, ammoniacal species, carbonate species, and acids and bases, the simultaneous uptake of N by a developing rice root system, and losses of NH₃ and CO₂ by volatilization from the floodwater. The equations allow for the initial distribution of urea and other reactants in the soil and floodwater, for movement both by diffusion and convection, and for the rates of urea hydrolysis, floodwater algal activity, organic-C and -N mineralization, and H+ release from roots to balance excess uptake of cations over anions. The equations are combined in a computer model which can predict the fate of N fertilizer in lowland ricefields for any combination of crop and environmental conditions.     

A simulation model for predicting soil moisture status

A simulation model has been developed to predict daily values of soil moisture content in the top 300 mm of the soil profile from simple meteorological and soil data. Daily precipitation is balanced against runoff, evapotranspiration and drainage. Proven procedures were adapted to calculate both runoff and evapotranspiration, the selection of the methods being influenced by the simplicity of the input data requirement and the essential accuracy of the results in relation to the complete model. Drainage for a given moisture content was calculated by means of exponential functions derived from experimental data of the hydraulic conductivities at field capacity and at saturation assuming a homogeneous soil profile. Good agreement was obtained between the predicted values of the soil moisture content and experimental data over a 4-year period for three typical Scottish soils both fallow and grass covered.     

Adsorption-desorption and leaching behaviors of broflanilide in four texturally different agricultural soils from China

Journal of Soils and Sediments - Broflanilide (BFL) is a new type of pesticide with broad prospects. However, it is not yet fully understood. With its wide application in the paddy field, it might...     

两种离子液体对Cd2+在四种土壤上吸附的影响

研究了2,3-吡啶二羧酸和咪唑-4,5-二羧酸两种离子液体阳离子部分对Cd2+在四种不同性质土壤上吸附的影响。结果表明,离子液体的存在显著影响了Cd2+在土壤中的吸附,与对照相比,添加1 mmol·L-12,3-吡啶二羧酸使得Cd2+在武进漂洗型水稻土、吴县潴育型水稻土、南京黄褐土和宜兴棕红壤四种土壤上的最大吸附量分别降低209、834、667、509 mg·kg-1,而添加1 mmol·L-1咪唑-4,5-二羧酸使Cd2+最大吸附量分别降低226、54、124、81 mg·kg-1,2,3-吡啶二羧酸对Cd2+在供试土壤上吸附量的影响显著大于咪唑-4,5-二羧酸。基于离子选择电极分析了平衡液中自由态Cd2+含量,发现两种离子液体都能与Cd2+络合,从而降低平衡液中Cd2+含量,其中2,3-吡啶二羧酸与Cd2+的络合能力大于咪唑-4,5-二羧酸。两种离子液体进入环境,会使Cd2+在土壤上的吸附量减少,从而增加Cd2+的移动性和环境风险。     

A study of phosphate adsorption by four Bangladesh soils

The adsorption curves for four soils were divided into segments I, II and III. Segment I ($\text{< 2}\text{μg P/ml equil. concn.}$) and segment II (2–150 μg P/ml equil. concentr.) conformed to the Langmuir equation similar to that of pure materials like gibbsite, pseudoboehmite and kaolinite, whereas segment III $\text{(> 75–150 μ}\text{g P/ml equil. concn.}\text{)}$ conformed to the Freundlich equation and was unlike the previous finding of linear relationship for pure materials.     

Comparison of two different methods to measure nitric oxide turnover in soils

 The NO turnover in soils was measured in two different experimental set-ups, a flow-through system, which is very time-consuming and needs rather sophisticated equipment, and a closed system using serum bottles. We compared the NO turnover parameters (NO consumption rate constant, NO production rate, NO compensation concentration) that were measured with both systems in different soils, under different conditions and in the presence of 10 Pa acetylene to inhibit nitrification. The values of the NO turnover parameters that were measured with the two systems under oxic conditions were usually comparable. The addition of acetylene did not affect the NO consumption rate constants of the soils with the exception of soil G1. However, the NO production rates and the NO compensation concentrations decreased significantly in the presence of acetylene, indicating that nitrification was the main source of NO in these soils. Only one soil (Bol) showed no nitrifying activity. Increasing soil moisture content resulted in decreasing NO consumption rate constants and NO production rates. Even at a high soil moisture content of 80% water holding capacity, nitrification was the main source of NO. The values of the NO turnover parameters that were measured with the two systems were not comparable under anoxic conditions. The NO consumption rate constants and the NO production rates were much lower in the closed than in the flow-through system, indicating that the NO consumption activity became saturated by the high NO concentrations accumulating in the closed system. Under oxic conditions, however, closed serum bottles were a cheap, easy and reliable tool with which to determine NO turnover parameters and to distinguish between nitrification and denitrification as sources of NO. Received: 21 April 1998     

A rapid method for predicting the lime requirement of acidic temperate soils with widely varying organic matter contents. III. A lime-quality correction model

A correction factor for lime quality ( F ), is described, which can be used to convert CaCO₃ requirements into recommendations for commercially available liming materials. A model is presented that relates values of F to the properties of both the liming materials and the soils to which the materials are applied. The results of independent tests demonstrate that the model is capable of predicting suitable values of F for a wide variety of different soil-lime treatments.
A procedure is described for estimating the amount of liming material required to adjust the pH in soils with widely varying organic matter contents. The procedure incorporates all the models and relationships developed in this study and appears to provide a more comprehensive method of evaluating the lime requirement of temperate acidic soils than any other method currently available.