石灰土壤原状土柱上硼和锌的迁移

Leaching of boron （B） and zinc （Zn） can be significant in some pedomorphic conditions, which can cause contamination of shallow groundwater and economic losses. Boron and Zn adsorption and transport was studied using 8.4 cm diameter × 28 cm long intact columns from two calcareous soil series with differing clay contents and vadose zone structures： Lyallpur soil series, clay loam （fine-silty, mixed, hyperthermic Ustalfic Haplargid）, and Sultanpur soil series, sandy loam （coarse-silty, mixed, hyperthermic Ustollic Camborthid）. The adsorption isotherms were developed by equilibrating soil with 0.01 tool L^-1 CaCl2 aqueous solution containing varying amounts of B and Zn and were fitted to the Langmuir equation. The B and Zn breakthrough curves were fitted to the two-domain convective-dispersive equation. At the end of the leaching experiment, 0.11 L 10 g L^-1 blue dye solution was also applied to each column to mark the flow paths. The Lyallpur soil columns had a slightly greater adsorption partition coefficient both for B and Zn than the Sultanpur soil columns. In the Lyallpur soil columns, B arrival was immediate but the peak concentration ratio （the concentration in solution at equilibrium/concentration applied） was lower than that in the Sultanpur soil columns. The breakthrough of B in the Sultanpur soil columns occurred after about 10 cm of cumulative drainage in both the columns; the rise in effluent concentration was fast and the peak concentration ratio was almost 1. Zinc leaching through the soil columns was very limited as only one column from the Lyallpur soil series showed Zn breakthrough in the effluent where the peak concentration ratio was only 0.05. This study demonstrates the effect of soil structure on B transport and has implications for the nutrient management in field soils.     

Determining differential water movement through ion exchange resin for nitrate leaching measurements

Abstract

The fate of fertilizer N applied to agricultural soils is of growing concern due to the potential for groundwater contamination. The recent development of an exchange resin that specifically absorbs NO₃ has led to the potential for a new technique to measure cumulative NO₃ leaching. The main limitation to the application of the resin technique is the matching of water movement through the resin with that of soil. A soil water movement device was developed to compare water movement through the resin to that of soil. A study was initiated to develop a resin/soil pack with water movement characteristics that closely matches those of natural soils. Three different soil types were used in this study: a Cahaba sandy loam (fine‐loamy, siliceous, thermic Typic Hapludult), a Congaree clay loam (fine loamy, mixed, nonacid, thermic Typic Udifluvent), and a Hiwassee clay (clayey, kaolinitic, thermic Typic Rhodudult). Both pure resin and resin mixed with soil were found to have higher water movement characteristics compared to bulk soil. A resin pack method was found which had water movement characteristics that were not significantly different from that of bulk soil for the three different soil types. The resin pack method is described.     

Zeolite Effects on Immobile Water Content and Mass Exchange Coefficient at Different Soil Textures

The concern for groundwater pollution by agrichemicals through solute movement within the soil is widespread. Zeolite is a type of soil amendment that is utilized to improve physical properties of soil and ameliorate polluted soil. The high negative charge of the zeolite and its open space structure allows adsorption and access of heavy metals and other cations and anions. The objectives of this research were (i) to determine the effects of different application rates of zeolite (0, 2, 4, and 8 g kg^?1) on the immobile water content and mass exchange coefficient in a loam soil and then (ii) to determine the effects of optimum application rate of zeolite on the immobile water content and mass exchange coefficient of sandy loam and clay loam soils in saturated conditions by a mobile and immobile (MIM) model. In a disturbed soil column, a method was proposed for determination of MIM model parameters, that is, immobile water content (θ_im), mass exchange coefficient (α), and hydrodynamic dispersion coefficient (D_h). Breakthrough curves were obtained for different soil textures with different zeolite applications in three replicates, by miscible displacement of chloride (Cl^?1) in disturbed soil column. Cl^?1 breakthrough curves were evaluated in terms of the MIM model. The results showed that the pore water velocity calculated based on the total soil volumetric water content (θ_im+ θ_m) and real pore water velocity calculated based on the mobile water content (θ_m) increased in the loam soil with an increase in zeolite application rate, so that, between these different rates of zeolite application, the maximum value of pore water velocity and real pore water velocity occurred at zeolite application rates of 8.6 and 11.5 g kg^?1, which are indicated as the optimum application rates. However, the comparison between different soils showed that the zeolite application rate of 8 g kg^?1 could increase pore water velocity of sandy loam and loam soils by 31% more than that of clay loam soil. The immobile water content and mass exchange coefficient of loam soil were correlated with the zeolite application rate and reduced with an increase in the rate of applied zeolite. In a comparison between different soils at zeolite application rate of 8 g kg^?1, the immobile water contents of the zeolite-treated soil decreased by 57%, 60%, and 39% on sandy loam, loam, and clay loam soils, respectively, compared with the untreated soil. Furthermore, zeolite application could reduce mass exchange coefficient by 9%, 43%, and 21% on sandy loam, loam, and clay loam soils, respectively. A positive linear relationship was found between θ_im and α. Zeolite application increased real pore water velocity of sandy loam soil by 39% and 46% compared with loam and clay loam soils, respectively. In other studies there was a decrease in ammonium and nitrate leaching due to the zeolite application, and therefore, an increase in real pore water velocity due to zeolite application in sandy loam soil, as compared with the loam and clay loam soils, may not show more rapid movement of solute and agrichemicals to the groundwater.     

Sorption and mobility of 14C-labeled imazaquin and metolachlor in four soils as influenced by soil properties

Aqueous batch-type sorption-desorption studies and soil column leaching studies were conducted to determine the influence of soil properties, soil and suspension pH, and ionic concentration on the retention, release, and mobility of [14C]imazaquin in Cape Fear sandy clay loam, Norfolk loamy sand, Rion sandy loam, and Webster clay loam. Sorption of [14C]metolachlor was also included as a reference standard. L-type sorption isotherms, which were well described by the Freundlich equation, were observed for both compounds on all soils. Metolachlor was sorbed to soils in amounts 2-8 times that of imazaquin, and retention of both herbicides was related to soil organic matter (OM) and humic matter (HM) contents and to herbicide concentration. Metolachlor retention was also related to soil clay content. Imazaquin sorption to one soil (Cape Fear) increased as concentration increased and as suspension pH decreased, with maximum sorption occurring in the vicinity of pK(a1) = (1.8). At pH levels below pK(a1) imazaquin sorption decreased as hydronium ions (H3O+) increased and competed for sites. NaCl was more effective than water in desorption of imazaquin at pH levels near the pK(a1). Mechanisms of bonding are postulated and discussed. The mobility of imazaquin through soil columns was in the order Rion > or = Norfolk > Cape Fear > or = Webster, whereas for metolachlor it was Rion > or = Norfolk > Webster > or = Cape Fear. Imazaquin was from 2 to 10 times as mobile as metolachlor.     

Cotton response to in-row subsoiling and potassium fertilizer placement in Alabama

In the USA a suggested method for correcting late season K deficiencies in cotton (Gossypium hirsutum L.) is by in-row deep placement of K fertilizer. Experiments were conducted on three Alabama soils (southeastern USA) for 3 years to evaluate cotton response to K fertilizer when surface broadcast with and without in-row subsoiling (to 38 cm depth) or deep placed in the in-row subsoil channel. Potassium was applied at rates ranging from 0 to 84 kg K ha⁻¹. Deep placement was achieved with a fertilizer applicator developed to distribute dry fertilizer at three depths down the back of the subsoil shank. All three soils also had deep placement treatments of 1680 kg ha⁻¹ agricultural limestone with and without 84 kg K ha⁻¹. Soils were an Emory silt loam (fine-silty, siliceous Fluventic Umbric Dystrochrepts), a Norfolk sandy loam (fine-loamy, siliceous Typic Kandiudults), and a Lucedale sandy clay loam (fine-loamy, siliceous Rhodic Paleuduts). All three soils had medium soil test K concentrations in the plow layer and medium or low concentrations of K at greater depths. The Norfolk soil had a well-developed traffic pan and in-row subsoiling increased seed cotton yields by an average of 22% during the 3 years of the study. Cotton responded to K fertilization in 2 out of 3 years at each location (6 out of 9 site-years) regardless of the method of K application. Annual applications of 84 kg K ha⁻¹ increased 3 year average seed cotton yields by 17%, 10% and 19% on the Emory, Norfolk and Lucedale soils, respectively. Deep placement of agricultural limestone with or without K fertilizer for cotton did not increase cotton yields.     

Nitrogen Mineralization Potential as Influenced by Microbial Biomass,Cotton Residues and Temperature

Integrating information on nitrogen (N) mineralization potentials into a fertilization plan could lead to improved N use efficiency. A controlled incubation mineralization study examined microbial biomass dynamics and N mineralization rates for two soils receiving 56 and 168 kg N ha^?1 in a Panoche clay loam (Typic Haplocambid) and a Wasco sandy loam (Typic Torriorthent), incubated with and without cotton (Gossypium hirsutum L.) residues at 10 and 25°C for 203 days. Microbial biomass activity determined from mineralized carbon dioxide (CO₂) was higher in the sandy loam than in clay loam independent of incubation temperature, cotton residue addition and N treatment. In the absence of added cotton residue, N mineralization rates were higher in the sandy loam. Residue additions increased N immobilization in both soils, but were greater in clay loam. Microbial biomass and mineralization were significantly affected by soil type, residue addition and temperature but not by N level.     

Soil Physical Properties and Bromide Movement in Relation to Tillage System

Abstract

Conventional (CT) and no‐tillage (NT) effects on soil physical properties and bromide (Br) movement were studied at two locations in North Carolina. The soils were a Norfolk sandy loam (fine‐loamy, siliceous, thermic Typic Paleudult) at a North American eastern Coastal Plain location and a Pacolet sandy clay loam (clayey, kaolinitic, thermic Typic Kanhapludult) at a Piedmont location. Bulk density (Db), macroporosity (Mp), and saturated hydraulic conductivity (Ks) were measured in the plant row (R) and trafficked (T) or untrafficked (N) interrow positions. Simulated rain was applied at two intensities to 1?m² plots after KBr was surface applied. The first simulated rain (30 min) consisted of a low (1.27 cm h^?1) or a high (5.08 cm h^?1) intensity applied 24 h after Br application. One week later, the high rainfall rate was repeated on all plots. Soil samples for Br determinations were taken 2 days after each rain simulation event to a depth of 40 cm and at the end of the growing season to 120 cm. Soil physical properties were affected by both tillage and position. Bulk density was greater for NT than for CT and in the T compared with R and N row positions. Mp was significantly greater in NT than CT at Coastal Plain location, but the results were opposite at the Piedmont location. Saturated hydraulic conductivity was highly variable ranging from 0.36 cm h^?1 to 14.4 cm h^?1 at the Coastal Plain location and from 0.06 cm h^?1 to 7.12 cm h^?1 at the Piedmont location. Saturated hydraulic conductivity at T position was about 100% lower than Ks at N and R positions, but the effect of tillage system was not significant on Ks. The surface 10 cm of soil contained the greatest Br concentration for both tillage systems. For the first and second sampling dates, greater Br movement occurred under NT vs. CT. However, no significant differences were observed in Br movement in the end of season sampling. Because of the coarser soil texture, greater Ks and Mp at the Coastal Plain location, Br moved, to a greater depth at this site than at the Piedmont site.     

Toxicity of brass powder to corn and the relationship to soil fractionation of copper and zinc

Abstract

The relationship of Cu and Zn fractionation in soils to plant growth was investigated on a Sassafras sandy loam (fine‐loamy, siliceous, mesic Typic Hapludult) and a Joppa gravelly sandy loam (loamy‐skeletal, siliceous, mesic Typic Hapludult). Pot studies were conducted in the greenhouse exposing corn (Zea mays cv. Silver Queen) to concentrations of 0, 100, 200, and 400 mg brass powder/kg soil. The corn was grown over a two week period, during which time individual plant heights were taken to note differences in plant growth. Data showed that plant height was reduced when the concentration of brass powder in the soil was increased. Total and fractionated Cu and Zn levels in the soils were analyzed and compared to height. Regression equations showed a more explicit relationship between height and exchangeable Cu levels rather than other Cu and Zn levels in the two soils. Additionally, a more pronounced effect was seen in plants grown on the Sassafras sandy loam, which was attributed to differences in soil physicochemical properties.     

Soil carbon and nitrogen dynamics as affected by long-term tillage and nitrogen fertilization

Quantifying seasonal dynamics of active soil C and N pools is important for understanding how production systems can be better managed to sustain long-term soil productivity especially in warm subhumid climates. Our objectives were to determine seasonal dynamics of inorganic soil N, potential C and N mineralization, soil microbial biomass C (SMBC), and the metabolic quotient of microbial biomass in continuous corn (Zea mays L.) under conventional (CT), moldboard (MB), chisel (CH), minimum tillage (MT), and no-tillage (NT) with low (45kgNha^–1) and high (90kgNha^–1) N fertilization. An Orelia sandy clay loam (fine-loamy, mixed, hyperthermic Typic Ochraqualf) in south Texas, United States, was sampled before corn planting in February, during pollination in May, and following harvest in July. Soil inorganic N, SMBC, and potential C and N mineralization were usually highest in soils under NT, whereas these characteristics were consistently lower throughout the growing season in soils receiving MB tillage. Nitrogen fertilization had little effect on soil inorganic N, SMBC, and potential C and N mineralization. The metabolic quotient of microbial biomass exhibited seasonal patterns inverse to that of SMBC. Seasonal changes in SMBC, inorganic N, and mineralizable C and N indicated the dependence of seasonal C and N dynamics on long-term substrate availability from crop residues. Long-term reduced tillage increased soil organic matter (SOM), SMBC, inorganic N, and labile C and N pools as compared with plowed systems and may be more sustainable over the long term. Seasonal changes in active soil C and N pools were affected more by tillage than by N fertilization in this subhumid climate. Received: 20 September 1996     

Saturated hydraulic conductivity in pedogenetic characterization of podzols with fragipans in quebec

Saturated hydraulic conductivity (K) values were measured in the laboratory on two podzolic soils (Spodosols) with fragipans developed from till deposits in the Appalachian and Laurentian Highlands of Quebec. The main difference between these tills lies in their contrasting textures. Due to the presence of coarse fragments and to a brittle and compact horizon, usual methods of measuring K in the field could not be used. Instead, blocks of soil were carved out and encased in paraffin. The technique insures minimum disturbance of the samples and accommodates variations in sample size due to stones.Sainte-Agathe sandy loam (sandy, mixed, frigid Fragiorthod) had higher K values than Arago loam (fine-loamy, mixed, frigid Fragiorthod) throughout the profile. In both soils, K decreased with depth largely as a result of an increase in bulk density. At any given bulk density, however, K was always lower in Arago than in Sainte-Agathe soil. This was attributed to illuviation and reorganization of particles within pores and partings. In the Arago profile, rearrangement of clay-size particles created an important vesicular porosity, thus closing off a portion of the pore volume to water transmission. In the Sainte-Agathe profile, material ranging from fine silt to clay was deposited selectively according to size class. Accessibility of the pore volume to percolating water was thus maintained.A second eluvial horizon Aex (A'2x) is present in the Arago, but not in the Sainte-Agathe soil, just above the fragipan, probably as a result of the very abrupt increase in bulk density from the podzolic B horizon to the fragipan. Water accumulating at the top of the fragipan seeps laterally, enhancing the eluviated character of the Aex horizon. Hydraulic conductivity was higher in this horizon than in over- and underlying horizons, although bulk density was greater.     

Classification of five pedons near Afgoi,Somalia

Five pedons representing the major soils on the Central Agricultural Research Station located on the Shabelle River floodplain near Afgoi (Somalia) were described and sampled. The samples were analyzed for particle-size distribution, pH, calcium carbonate equivalent, electrical conductivity and sodium adsorption ratio. According to Soil Taxonomy, three pedons were classified as Udic Chromusterts, very fine, isohyperthermic; one as a Udic Chromustert, fine isohyperthermic; and one as a Typic Ustifluvent, fine-loamy isohyperthermic. Four of the pedons were classified as Chromic Vertisols and the fifth as a Calearic Fluvisol according to legend of the FAO-Unesco soil map of the world.     

Changes in Soil Test Phosphorus from Broiler Litter Additions

Abstract

Nutrient surpluses on the Delmarva Peninsula have led to a continual accumulation of soil test phosphorus (STP), a potential source for transport of phosphorus (P) to surface waters. This article examines the effects of initial soil test P concentrations and broiler litter additions on STP accumulation. Broiler litter (BL) was applied at rates of 0, 2.5, 5, 7.5, and 10 g kg^?1 (dry weight) to three soils: an Evesboro sandy loam (Mesic, coated Typic Quartzipsamments), a Pocomoke sandy loam (coarse‐loamy, siliceous, thermic typic Umbraquults), and a Matapeake silt loam (fine‐silty, mixed, semiactive, mesic Typic Hapludults). Soils and BL were incubated for 16 weeks with subsamples analyzed after 4 and 16 weeks. There was a linear increase in STP (Mehlich‐3), water‐soluble P (WS‐P), iron‐oxide strip‐extractable P (FeO‐P), and Mehlich‐3 phosphorus saturation ratio (M3‐PSR) with broiler litter additions. Regression analysis indicated few significant differences in STP response to added BL between soils within the same soil group having different initial STP levels. Correlation analysis and stepwise regression indicated that increases in WS‐P and FeO‐P from added BL were more closely related to the degree of P saturation of the soil rather than traditional STP measurements. Therefore, decisions regarding manure placement within a watershed should be based on the potential P sorption capacity of the soil as well as potential P transport pathways when the goal is the reduction of P transfer to waterbodies.     

Tillage effects on soil properties at different levels of fertilizer application in Punjab, Pakistan

The effects of cropping systems and management practices on soil properties provide essential information for assessing sustainability and environmental impact. Tillage and fertilizer rates were evaluated for their effects on soil bulk density (BD), penetration resistance, soil organic carbon (SOC) concentration and availability of macronutrients on a sandy clay loam (fine-loamy, mixed, hyperthermic Typic Haplargids, USDA; Luvic Yermosol, FAO) in a semi-arid region of Pakistan. Wheat (Triticum aestivum L.) and cotton (Gossypium hirsutum L.) were double-cropped from 1996 to 1998. Tillage treatments were minimum till (MT), conventional till (CT), and deep till (DT). Low, medium and high fertilizer rates were applied to wheat and cotton. BD was affected neither by tillage nor fertilizer rates. Soil penetration resistance was lower for DT than CT and MT. Tillage methods affected soil P concentration but did not affect N and K concentrations. However, fertilizer application significantly increased soil P and K concentrations. Concentrations of N, P, K and SOC were greater in the plough layer than sub-soil. Grain yield of wheat was significantly negatively correlated with penetration resistance and was positively correlated with soil P and K concentrations. Yield of cotton was significantly negatively correlated with soil BD. These data provide an experimental basis to re-evaluate recommendations for fertilizer rates and tillage methods for production of wheat and cotton in Punjab. Further, there is a strong need to establish long-term experiments to study agronomic and environmental effects of tillage methods, fertilizer rates, and cropping systems on productivity and environment quality.     

推求土壤水分运动参数的简单入渗法──Ⅱ.实验验证

预报土壤中水分流动需要的土壤导水特性可通过观察水平土柱的入渗过程来确定,这一观测过程的分析是基于对Ｒｉｃｈａｒｄｓ方程求积分解。土壤水分特征曲线中的参数由观测的水平土柱和特征湿润长度和吸力为确定,非饱和土壤导水率由已确定的特征曲线中的参数和测定的饱和导水率导出。供试土壤有三种,它们的质地从砂壤到粘壤。由这种方法所确定的这三种土壤的水分特征曲线与实测的特征曲线符合良好,所确定的砂壤的非饱和导水率与实     

Lime application to reduce phosphorus release in different textured intact and small repacked soil columns

Purpose

Phosphorus (P) losses from agricultural fields through leaching are the main contributors to eutrophication of lakes and rivers in North America. Adoption of P-retaining strategies is essential to improve the environmental quality of water bodies. The main objective of this study is to evaluate lime as a soil amendment in reducing phosphorus concentration in the leachate from three common soil textures with neutral to alkaline pH.

Materials and methods

Phosphorus leaching from undisturbed soil columns (10 cm in diameter and 20 cm deep) as well as small repacked columns was investigated and compared in this study. Lime (high calcium hydrated lime) at the rate of 1% by air-dried soil mass was applied to the topsoil of the columns. Both sets of experiments followed a full factorial design with two factors of soil texture at three levels (sandy loam, loam, and clay loam) and treatment at two levels (control and limed) with three replicates. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy was performed on the control and limed soil samples to confirm the formation of calcium phosphate compounds.

Results and discussions

For both intact and repacked columns, dissolved reactive phosphorus (DRP) concentrations in the leachates from limed sandy loam and limed loam soil columns was significantly reduced, while DRP in the limed clay loam column leachates was not changed. Elemental mapping demonstrated that in limed sandy loam and loam soils, the calcium loadings on the soil surface were always linked with phosphorus. The formation of calcium phosphate compounds and the increased phosphate adsorption on the soil surface through Ca bridging could be the two main phosphorus-lime retention mechanisms. Total dissolved phosphorus (TDP) in the leachates of limed loam and limed clay loam indoor intact and repacked columns was reduced, while there was no change in that of the sandy loam soil. In finer textured soils, lime can increase TDP retention through the immobilization of organic phosphates.

Conclusions

The impact of lime application on DRP and TDP varied with the soil texture. The lime-induced reduction in the DRP and TDP was variable between the intact and repacked columns demonstrating the importance of soil structure on phosphorus and lime interactions in the soil. Overall, lime application at the studied rate can be considered a promising soil amendment in mitigating phosphorus loss from non-calcareous neutral to alkaline soils.

     

Adsorption and leaching behaviour of the herbicide alachlor (2-chloro-2', 6'diethyl-N-(methoxymethyl) acetanilide) in a soil specific management

Abstract. Uniform application rates of fertilizers and herbicides may result in over-treating some soils and under-treating others; costs may be unnecessarily large and soil, ground water and surface waters may be contaminated. An alternative is site specific treatment, tailored to individual soil types present in agricultural fields of any size. To study the pollution hazards of the herbicide alachlor, leaching and adsorption experiments used disturbed samples and undisturbed soil columns. Adjoining Ves, Normania and Webster soil series (Udic Haplustoll; Aquic Haplustoll; Typic Haplaquoll) were sampled and analysed for various properties. Ring uniformly ¹⁴C-labelled alachlor was used to study adsorption and leaching characteristics in these soils. Results show different alachlor behaviour in topsoil and subsoil layers.     

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.     

Runoff and leaching of alachlor under conventional and soil-specific management

Abstract. The influence of conventional and soil-specific management on leaching and runoff losses of soil-applied alachlor (2-chloro-2',6'-diethyl- N -(methoxymethyl) acetanilide) was studied across a soil catena (landscape) with varied slope and drainage characteristics. The catena consisted of: a well-drained Ves (fine-loamy, mixed, mesic Udic Haplustoll) soil on the backslope (1–4%), a Ves soil on the sideslope (6–12%), and a poorly drained Webster (fine-loamy, mixed, mesic Typic Haplaquoll) soil on the toeslope (0–3%). In general, the concentration of alachlor in runoff water was greater in the Ves soil than in the Webster. In 1992 alachlor concentrations in runoff (water, sediment + water) were less for soil-specific rates (2.20 or 2.80 kg/ha) than for a uniform rate (3.36 kg/ha) in both Ves soils. There was no significant difference in alachlor concentration related to application rates (soil-specific rate 3.66 kg/ha) in the runoff from the Webster soil. Averaged across soils and events, the concentrations of alachlor in runoff (water, sediments + water) were less for soil-specific rates than for the uniform rate. Alachlor was not detected in soil samples obtained from depths greater than 15 cm in any soil or treatment after the first sampling. At the first sampling in 1992 (7 days after application) alachlor was detected down to 45 and 90 cm in the Ves and Webster soils, respectively. Detectable amounts (≥0.1 μg/1) of alachlor were observed in soil water samples extracted from all three soils during some sampling dates. No particular trends were observed with soils or application rates.     

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.     

A study of some tillage practices for sustainable crop production in India

Soil tilth has been defined in terms of a ‘Physical Index’ based on the product of the ratings of eight physical properties — soil depth, bulk density, available water storage capacity, cumulative infiltration or apparent hydraulic conductivity, aggregation or organic matter, non-capillary pore space, water table depth and slope. The Physical Index and a tillage guide were used to identify the tillage requirements of different soils varying in texture from loamy sand to clay in the semi-arid tropics. The physical index was 0.389 for a loamy sand, 0.518 for a black clay loam and 0.540 for a red sandy loam soil and the cumulative rating indices in summer and winter seasons were 45 and 44 for loamy sand, 52 and 51 for red sandy loam and 54 and 52 for black clay loam soils, respectively. The compaction of the loamy sand by eight passes of a 490 kg tractor-driven roller (0.75 m diameter and 1.00 m length) increased the physical index to 0.658 and chiselling of the red sandy loam and black clay loam increased the physical indices to 0.686 and 0.729, respectively. The grain yields of rainfed pearl millet and guar and irrigated pearl millet, wheat and barley increased significantly over the control (no compaction) yields by compaction.

The chiselling of the soils varying in texture from loamy sand to clay at 50 to 120-cm intervals up to 30–40 cm depth, depending upon the row spacing of seedlines and depth of the high mechanical impedance layer, increased the grain yields of rainfed and irrigated maize on alluvial loamy sand, rainfed maize on alluvial sandy loam and red sandy loam, rainfed sorghum on red sandy loam and black clay loam, irrigated sorghum on black clay loam and rainfed black gram on red sandy loam, pod yield of rainfed groundnut, tuber yield of irrigated tapioca and fresh fruit yield of rainfed tomato on red sandy loam and sugarcane yield on black clay soil, significantly over the yields of no-chiselling systems of tillage such as disc harrow and country plough.