Depth distribution and bioavailability of pollutants in long-term differently tilled soils

Pollutants can be introduced to soil through the application of organic and inorganic fertilizers and pesticides and through atmospheric depositions. The objective of this research was to evaluate the influence of long-term (9–17 years) tillage systems on the behavior of pollutants in soils. Bioavailability and enrichment of heavy metals, arsenic, and organics, i.e. polychlorinated biphenyls (PCB’s) and a chlorinated phenol (2,4-DCP) were measured in a Eutric Cambisol and a Luvisol under conventional tillage (CT), reduced tillage (RT), and no-tillage (NT). Soil samples were collected from 0 to 3, 3 to 10, and 10 to 25 cm depths.

The upper layer of NT soils was enriched in pollutants, but concentrations decreased with increasing soil depth. Atmospheric deposition of pollutants and input via organic fertilizers was noticeable in soils under long-term NT. Total amount of zinc (59 mg kg⁻¹) was significantly enriched in the 0–3 cm depth of the Luvisol under NT and this was attributed to higher sorption capacity for heavy metal input via liquid manure. In the Eutric Cambisol, NT resulted in significant increase of cadmium extracted by aqua regia in the arable layer of 0–25 cm. As a result of higher soil organic C, long-term accumulation of PCB’s in NT soils was more pronounced than in plowed soils. In plowed soils the mixing effect resulted in homogeneous distribution of pollutants within a soil depth of 0–25 cm.

The enrichment of organic C in RT and NT soils emphasizes the role of soils as a sink for pollutants, buffering the contaminants against leaching and transfer into crops.     

Effects of tillage depth on organic carbon content and physical properties in five Swedish soils

The soil tillage system affects incorporation of crop residues and may influence organic matter dynamics. A study was carried out in five 15–20 year old tillage experiments on soils with a clay content ranging from 72 to 521 g kg⁻¹. The main objective was to quantify the influence of tillage depth on total content of soil organic carbon and its distribution by depth. Some soil physical properties were also determined. The experiments were part of a series of field experiments all over Sweden with the objective of producing a basis to advise farmers on optimal depths and methods of primary tillage under various conditions. Before the experimental period, all sites had been mouldboard ploughed annually for many years to a depth of 23–25 cm. Treatments included primary tillage to 24–29 cm depth by mouldboard plough (deep tillage) and to 12–15 cm by field cultivator or mouldboard plough (shallow tillage). Dry bulk density, degree of compactness and penetration resistance profiles clearly reflected the depth of primary tillage and substantially increased below that depth. Compared to deep tillage, shallow tillage increased the concentration of organic carbon in the surface layer but decreased it in deeper layers. Total quantity of soil organic carbon and carbon–nitrogen ratio were unaffected by the tillage depth. Thus, a reduction of the tillage depth from about 25 cm to half of that depth would appear to have no significant effect on the global carbon cycle.     

Fine-earth translocation by tillage in stony soils in the Guadalentin, south-east Spain: an investigation using caesium-134

Tillage erosion is increasingly recognised as an important soil erosion process on agricultural land. In view of its potential significance, there is a clear need to broaden the experimental database for the magnitude of tillage erosion to include a range of tillage implements and agricultural environments. The study discussed in this paper sought to address the need for such data by examining tillage erosion by a duckfoot chisel plough in stony soils on steep slopes in a semi-arid environment. Results of the investigation of coarse fraction (rock fragment) translocation by tillage in this environment have been presented elsewhere and the paper focuses on tillage translocation and erosion of the fine earth. Tillage translocation was measured at 10 sites, representing both upslope and downslope tillage by a duckfoot chisel plough on five different slopes, with tangents ranging from 0.02 to 0.41. A fine-earth tracer, comprising fine earth labelled with ¹³⁴Cs, was introduced into the plough layer before tillage. After a single pass of the plough, incremental samples of plough soil were excavated and sieved to separate the fine earth from the rock fragments. Translocation of the fine-earth tracer was established by analysing the ¹³⁴Cs content of the samples of fine earth. These data were used to establish translocation distances for each combination of slope and tillage direction. Translocation distances of the fine earth were not significantly different from translocation distances of the coarse fraction. For all sites, except uphill on the 0.41 slope, translocation distances were found to be linearly related to slope tangent. The soil flux due to tillage for each site was calculated using the translocation distance and the mass per unit area of the plough layer. For slopes with tangents <0.25, the relationship between soil flux and tangent was linear and the soil flux coefficient derived was 520–660 kg m⁻¹ per pass. This is much larger than the coefficients found in other studies and this high magnitude is attributed to the non-cohesive nature and high rock fragment content of the soil in this investigation. A second contrast with previous studies was found in non-linearity in the relationship between soil flux and tangent when steeper slopes were included. This was a product of variation in plough depth between the steepest slopes and the remainder of the study area. On the basis of the study it is suggested that an improved understanding of tillage erosion may be obtained by considering the dual processes of tillage detachment (mass per unit area of soil subject to tillage) and tillage displacement (equivalent to translocation distance per pass) in assessing, comparing and modelling tillage translocation. An improved model is proposed that recognises the complexity of soil redistribution by tillage, provides a framework for process-based investigation of the controls on tillage fluxes, and allows identification of potential self-limiting conditions for tillage erosion.     

Estimation of critical limit for zinc in rice soils

Abstract

Twenty surface soil samples wore collectod from Nalnltal Tarai (foot‐ hills of Himalya) where ‘Khaira’ disease (Zn deficiency disease of rice) was prevalent. Rice (Oryza sativa L. variety IR ‐ 8) was grown in pots for 8 weeks after transplanting. Experiments were carried out to find the suitability of five soil Zn extractants viz. dilute acid (HC1 ‐ H₂SO₄) mixture, DTPA‐ (NH₄) ₂CO₃, pH 7.3, dithizono, NH₄ ‐ Ac, pH 4.6 and MgCl₂. Critical limits of available Zn in soils were established for rice crop by old and new Cate and Nelson procedures.

Zn extracted from the soil with NH₄ ‐ Ac, pH 4.6, dithlzono, MgCl₂, and DTPA‐(NH₄) ₂CO₃, pH 7.3 was significantly correlated with the uptake of Zn by the rice plants. The correlation of Zn uptake with dilute acid mixture extractable Zn was not significant. The extractant which extracted more Zn gave higher values of critical limit and vice versa. It is concluded that all extracting solutions except dilute acid mixture were found to be suitable for predicting available Zn in rice soils of Taral.     

Soil organic carbon and fly-ash distributions in eroded phases of soils in Illinois and Russia

Soil organic carbon (SOC) dynamics are affected by tillage, soil erosion and depositional processes. The objectives of this paper are to evaluate soil organic carbon and fly-ash distribution methods for identifying eroded phases of soils in Illinois and Russia and quantifying the extent of soil loss from erosion. The effect of accelerated erosion on soils is recorded on National Cooperative Soil Survey maps as phases of soil series that reflect the percentage of the original A horizon materials remaining. Identification depends on knowledge of the original A horizon thicknesses, SOC and fly-ash contents at uncultivated and uneroded sites when determining erosion phases of soil at cultivated and eroded sites. However, locating uncultivated and uneroded comparison sites with similar landscape and slope characteristics can be difficult. The amount of A horizon materials within the plow layers (Ap horizons) or topsoils are often determined by soil colors which reflect the SOC contents. Soil erosion phases based on original A horizon materials remaining in the topsoils may underestimate the extent of soil losses from topsoils and subsoils, particularly where soils have been cultivated for hundreds of years and are severely eroded. The SOC contents and soil erosion phases can be affected by losses or gains of organic C-rich sediments from tillage translocation and erosion, by management input level differences, oxidation, or as a result of land use and landscape position variations. Fly-ash was found to be more stable and act as a better indicator of soil erosion phase than SOC content.     

Soil organic carbon changes after 12 years of no-tillage and tillage of Grantsburg soils in southern Illinois

Many factors including management history, soil type, climate, and soil landscape processes affect the dynamics of soil organic carbon (SOC). The primary objective of this research was to determine the effects of no-tillage and tillage systems on the SOC content after 12 years of controlled treatments. A tillage experiment with three treatments (no-till (NT), chisel plow (CP) and moldboard plow (MP)) was initiated in the spring of 1989 in southern Illinois. The plot area was previously in a tall fescue hayland for 15 years and had a 6% slope. Maize (Zea mays L.) and soybean (Glycine max L. Merr.) were grown in the plot area on a yearly rotation system starting with maize. Periodically, the SOC content of various soil layers, to a depth of either 30 or 75 cm, was measured and expressed on both a gravimetric and volumetric basis. After 12 years, the 0–15 cm surface soil layer of MP was significantly lower in SOC than the NT and CP plots. For all but 2 values, the significance of findings did not change with the form of expression (gravimetric versus volumetric). The surface layer (0–15 cm), subsoil (15–75 cm), and rooting zone (0–75 cm) of all treatments had reduction in SOC on a volumetric basis when compared to the pre-treatment values for sod. At the end of the 12-year study, the MP system had significantly less SOC in the surface layer, subsurface layer and rooting zone than the NT system at comparable depths. After 12 years of tillage under a maize–soybean rotation, the NT treatment sequestered or maintained more SOC stock (47.0 Mt ha⁻¹) than the CP (43.7 Mt ha⁻¹) and MP (37.7 Mt ha⁻¹) treatments. The annual rate of SOC stock build up in the root zone (0–75 cm), above the MP system base, was 0.71 Mt ha⁻¹ year⁻¹ for the NT system and 0.46 Mt ha⁻¹ year⁻¹ for the CP system. For land coming out of the Conservation Reserve Program and returning to row crop production, NT and CP systems would maintain more SOC stock than MP system and reduce CO₂ emissions to the atmosphere.     

Tillage and residue management effects on β-glucosaminidase activity in soils

There is an increasing interest in assessing the effects of tillage systems and residue management on biochemical processes, especially enzyme activities, of soils. This study was carried out to investigate the effects of three tillage systems (no-till, chisel plow and moldboard plow) and four residue placements (bare, normal, mulch and double mulch) on the activity of N-acetyl-β-glucosaminidase (NAGase, EC 3.2.1.30) involved in C and N cycling in soils. The activity values were significantly affected by tillage and residue management practices, being greatest in soils with no-till/double mulch and least with no-till/bare and moldboard/normal. Also, they were the highest under no-till/ double mulch-treated soils. Linear regression analyses showed that the activity of NAGase was significantly correlated with organic C in the surface soils (r=0.89***) and with organic C content at different depths (r=0.97***). The NAGase activity values were significantly correlated with the arylamidase activity values of the soils (r=0.63**), suggesting that tillage and residue management practices have similar impacts on the activities of these enzymes. The activity of this enzyme decreased markedly with increasing depth of the surface soil (0-15 cm) of the no-till/ double mulch-treated plots.     

土壤胶体理化性质对其稳定性和可移动性的影响研究

采用长春市具有代表性的阶地农田的黏壤土、河漫滩的细砂土和黄土台地的粉壤土为基质,以提取的土壤胶体为对象,采用实验室模拟方法研究了土壤胶体理化性质对其稳定性和可移动性的影响。研究结果表明3种土壤胶体的临界絮凝浓度(CFC),与伊利石/蒙脱石矿物含量成反比并随着矿物含量的增大而降低,可能是因为伊利石/蒙脱石矿物是易絮凝矿物,水化驱动力及水化后的不稳定性较大;去除游离氧化铁后的农土去铁胶体提高了稳定性,而黄土去铁胶体和河土去铁胶体降低了稳定性,主要是由不同的土壤胶体去除游离氧化铁后性质改变程度不一样引起的;去除有机质后的农土去有机质胶体、黄土去有机质胶体和河土去有机质胶体降低了CFC,并且降低程度是与土壤胶体的有机质含量成反比。     

Effects of liming and tillage systems on microbial biomass and glycosidases in soils

This study was undertaken to investigate the long-term influence of lime application and tillage systems (no-till, ridge-till and chisel plow) on soil microbial biomass C (C_mic) and N (N_mic) and the activities of glycosidases (- and -glucosidases, - and -galactosidases and -glucosaminidase) at their optimal pH values in soils at four agroecosystem sites [Southeast Research Center (SERC), Southwest Research Center (SWRC), Northwest Research Center (NWRC), and Northeast Research Center (NERC)] in Iowa, USA. Results showed that, in general, the C_mic and N_mic values were significantly (P <0.001) and positively correlated with soil pH. Each lime application and tillage system significantly (P <0.001) affected activities of the glycosidases. With the exception of -glucosidase activity, there was no lime×tillage interaction effect. Simple correlation coefficients between the enzyme activities and soil pH values ranged from 0.51 (P <0.05) for the activity of -glucosidase at the NWRC site (surface of the no-till) to 0.98 (P <0.001) at the SWRC site. To assess the sensitivity of the enzymes to changes in soil pH, the linear regression lines were expressed in activity/pH values. In general, their order of sensitivity to changes in soil pH was consistent across the study sites as follow: -glucosidase>-glucosaminidase>-galactosidase>-galactosidase>-glucosidase. Lime application did not significantly affect the specific activities (g p -nitrophenol released kg^–1 soil organic C h^–1) of the enzymes. Among the glycosidases studied, -glucosidase and -glucosaminidase were the most sensitive to soil management practices. Therefore, the activities of these enzymes may provide reliable long-term monitoring tools as early indicators of changes in soil properties induced by liming and tillage systems.     

Determining weathering rates of soils in China

As an important parameter for critical load calculation and soil acidification simulation, weathering rates of soils in China were studied using different methods of calculation. The approaches used were the mass balance approach, the soil mineralogical classification, the total analysis correlation, the PROFILE model, the MAGIC model and a simulated leaching experiment. Since chemical weathering of secondary minerals usually plays a much more important role in neutralizing the long-term acidification of soils in China than that of parent material, soil mineralogy rather than parent rock/material type, which is regarded as the most suitable factor representing weathering rates in Europe, should be adopted as the basis for soil classification. The weathering rate assigned to each soil should also be corrected when the effect of temperature is considered. Due to the variation in experimental conditions, the weathering rates of soils from laboratory experiment may be difficult to compare with field determined rates, and should be adjusted by pH and percolation rate. The comparison of various methods in this study shows that the weathering rates of soils estimated by the PROFILE model coincide well with those from other independent methods such as the dynamic modeling by MAGIC and the modified leaching experiment. The weathering rates were very low (usually lower than 1.0 kEq·ha⁻¹·year⁻¹) for Allites (including Latosol, Lateritic Red Earth, Red Earth, Yellow Earth and Yellow-Brown Earth) in south China and Silalsols (consisting of Dark Brown Forest Soil, Black Soil and Podzolic Soil) in northeast China, and very high for Alpine Soils, Desert Soils and Pedocals in west China. The content of weatherable minerals in soil is the most important factor in determining the spatial distribution of weathering rate in China, while the difference in temperature may be the reason why the weathering rate of soil in northeast China was lower than that in southeast China.     

Total and labile soil organic nitrogen as influenced by crop rotations and tillage in Canadian prairie soils

Crop rotations and tillage practices influence the quantity and quality of soil organic N (SON). We evaluated the impact of crop rotations and tillage practices on SON and mineralizable N at a depth of 0–15 cm in six field experiments, varying in duration over 8–25 years, that were being conducted in three Chernozemic soil zones in Saskatchewan, Canada. In a Brown Chernozem, continuous wheat increased SON at 0–15 cm by 7–17 kg N ha^–1year^–1 more than fallow/wheat. In a Dark Brown Chernozem, continuous cropping increased SON by 30 kg N ha^–1year^–1, compared with cropping systems containing fallow once every 3 years; and, in a Rego Black Chernozem, the increase in SON was 29 kg N ha^–1 year^–1, compared with cropping systems containing fallow once every 4 years. The increase in SON due to increased cropping frequency was accompanied by an increase in the proportion of mineralizable SON in the Brown Chernozem, but not in the Dark Brown and Black Chernozems. In the Brown Chernozemic soil zone, no-tillage management increased SON, compared with conventional tillage, varying from 16 kg N ha^–1year^–1 to 28 kg N ha^–1year^–1. In the Dark Brown Chernozemic soil zone, it increased SON by 35 kg N ha^–1year^–1 and, in the Black Chernozemic soil zone, by about 40 kg N ha^–1year^–1. Increases in SON at a depth of 0–7.5 cm due to no-tillage management was accompanied by a greater increase in the mineralizable N for Hatton fine sandy loam, Melfort silty clay and Indian Head clay than for other soils, indicating that the material responsible for the increased SON due to no-tillage was more labile than the soil humus N. However, the increased SON under no-till in Swinton loam, Sceptre clay and Elstow clay loam was not associated with an increase in the mineralizable N, indicating that this increased SON was no more susceptible to decomposition than the soil humus N. Therefore, increases in SON under improved management practices, such as conservation tillage and extended crop rotations, do not necessarily increase the potential soil N availability.     

Enzyme activities and microbial community structure in semiarid agricultural soils

This study investigated the effect of management on -glucosidase, -glucosaminidase, alkaline phosphatase, and arylsulfatase activities and the microbial community structure in semiarid soils from West Texas, USA. Surface samples (0–5 cm) were taken from a fine sandy loam, sandy clay loam, and loam that were under continuous cotton ( Gossypium hirsutum L.) or in cotton rotated with peanut ( Arachis hypogaea L.), sorghum ( Sorghum bicolor L.), rye ( Secale cereale) or wheat ( Triticum aestivum L.), and had different water management (irrigated or dryland), and tillage (conservation or conventional). The enzyme activities were higher in the loam and sandy clay loam than in the fine sandy loam. Soil pH was not affected by management, but the soil organic C and total N contents were generally affected by the different crop rotations and tillage practices studied. The trends of the enzyme activities as affected by management depended on the soil, but in general crop rotations and conservation tillage increased the enzyme activities in comparison to continuous cotton and conventional tillage. The soil enzyme activities were significantly correlated with the soil organic C ( r -values up to 0.90, P< 0.001), and were correlated among each other ( r -values up to 0.90, P <0.001). There were differences in the fatty acid methyl ester profiles between the fine sandy loam and the sandy clay loam and loam, and they reflected the differences in the enzyme activities found among the soils. For example, a 15:0 ranged from 1.61±0.25% in cotton-peanut/irrigated/no-till in the fine sandy loam to 3.86±0.48% in cotton-sorghum/dryland/conservation tillage in the sandy clay loam. There were no differences due to management within the same soil.Trade names and company names are included for the benefit of the reader and do not infer any endorsement or preferential treatment of the product by USDA-ARS     

The use of remote sensing to detect the consequences of erosion in gypsiferous soils

Tillage practices on sloping ground often result in unsustainable soil losses impairing soil functions such as crop productivity, water and nutrients storage, and soil organic carbon (SOC) sequestration. A sloping olive grove (10%) was planted in shallow gypsiferous soils in 2004. It was managed by minimum tillage; the most frequent management practice in central Spain. The consequences of erosion were studied in soil samples (at 0–10, 10–20, and 20–30 cm depths) by analyzing SOC, available water and gypsum content, and by detecting spectral signatures using an ASD FieldSpecPro® VIS/NIR-spectroradiometer. The Brightness index (BI), Shape index (FI), and Normalized Difference Vegetation Index (NDVI) were derived from the ASD spectral signatures and from remote sensing (Sentinel-2 image) data. The development of these young olive trees was estimated from the measured diameter of the trunks (17 ± 18 cm diameter). In 20–30 cm of the soil, the carbon stock (38 ± 18 Mg ha⁻¹) as well as the available water content (12 ± 6%) was scarce, affecting the productivity of the olive grove. The above-mentioned indices obtained from the laboratory samples and the pixels of the Sentinel-2 image were significantly (p < 0.01) correlated, with a correlation coefficient of around 0.4. The BI was related to the gypsum content and the slope of the plot. The FI was related to the carbon and water contents. The NDVI derived from the satellite image identified the influence of soil degradation on the trees and the carbon content. The spatial-temporal changes of the indices might help in tracking soil changes over time.     

Bulk density by Proctor test as a function of texture for agricultural soils in Maputo province of Mozambique

Soil degradation processes may be of various kinds, including soil compaction. The present study was carried out with the objective of assessing the sensitivity of agricultural or recently abandoned soils in Maputo province of Mozambique to compaction. The assessment is based on the maximum of bulk density attained using the Proctor test (MBD).

In this study the soil texture is expressed by silt plus clay (S + C) or clay (C). The relations between the soil texture and MBD, and between soil texture and critical water content (CWC—soil water at which MBD is attained) were determined. Selected soils range from 10 to 74% of S + C and 9 to 60% of C.

The results suggest there is a relationship between the considered parameters, being that between S + C and MBD or CWC, the best. For MBD the relationship is represented by two quadratic equations with the boundary in between these being a S + C value of 25% and C value of 20%.

Based on the obtained results, one can conclude that the selected parameters may be a useful basis for estimation of the sensitivity to compaction of the Maputo province's soils. It is recommended that similar studies be carried out for soils under forest land and for soil of other provinces to establish the national physical degradation hazard as a function of soil parameters determined routinely and at low cost. The suggested parameters are texture and soil organic matter (SOM).     

Spatio-temporal variation of anisotropy of saturated hydraulic conductivity in a tilled sandy loam soil

Knowledge on anisotropy of saturated hydraulic conductivity can improve the understanding of transport phenomena in soil. We hypothesized that saturated hydraulic conductivity (K_s) in the upper part of the root zone of an agricultural sandy loam soil was anisotropic at different soil depths and times after tillage. K_s was measured on undisturbed 100 cm³ core samples taken in the horizontal and vertical directions in up to four soil layers (Surf: surface layer (0–5 cm); Top: topsoil (10–15 cm); Trans: transition layer between topsoil and subsoil; Sub: subsoil (40–60 cm)) 1, 8 and 32 months, respectively, after mouldboard ploughing and drilling. The ratio between estimated geometric mean values for K_s in the vertical and the horizontal directions (K_ms,v/K_ms,h) was used to test the hypotheses. A total of 669 soil samples were analysed.K_ms,v/K_ms,h varied with time after tillage and between soil layers. One month after ploughing, K_ms,v/K_ms,h was <0.23 (P = 0.975) in the Trans layer with an average value of 0.084, i.e. K_ms,h was 12 times larger than K_ms,v. Anisotropy could not be documented in this layer 8 or 32 months after ploughing, i.e. K_ms,v/K_ms,h was not significantly different from 1.0. For the Surf and Top layers 32 months after ploughing, K_ms,v/K_ms,h was in the intervals 1.4–50 and 3.1–77, respectively, (P = 0.95) with average values of 8.4 and 15, respectively. Thus, K_ms,v was 8.4 respectively 15 times larger than K_ms,h in the two layers. Anisotropy was not found in these layers 1 or 8 months after tillage. Strong anisotropy was found in the Sub layer with K_ms,v/K_ms,h averaging to 14 and 32, respectively, 8 and 32 months after tillage. K_ms,v and K_ms,h generally decreased with time in the Surf, Top and Trans layers, except in the vertical direction in the Top layer between 8 and 32 months after ploughing, and in the Trans layer between 1 and 8 months after ploughing. Overall, the geometric means of K_s varied between 10^−4.0 and 10^−7.1 m s⁻¹.The results may reflect systematic effects of soil settlement and drying/wetting phenomena coupled with biological activity and the existence of stable, vertically oriented biopores in the subsoil. It appears to be necessary to consider anisotropy of K_s and its variation in the analysis and modelling of water flow and chemical transport in agricultural soils, particularly to explain heterogeneous flow phenomena at the plot and field scales.     

Tillage effects on microbial biomass and nutrient distribution in soils under rain-fed corn production in central-western Mexico

Quantifying how tillage systems affect soil microbial biomass and nutrient cycling by manipulating crop residue placement is important for understanding how production systems can be managed to sustain long-term soil productivity. Our objective was to characterize soil microbial biomass, potential N mineralization and nutrient distribution in soils (Vertisols, Andisols, and Alfisols) under rain-fed corn (Zea mays L.) production from four mid-term (6 years) tillage experiments located in central-western, Mexico. Treatments were three tillage systems: conventional tillage (CT), minimum tillage (MT) and no tillage (NT). Soil was collected at four locations (Casas Blancas, Morelia, Apatzingán and Tepatitlán) before corn planting, at depths of 0–50, 50–100 and 100–150 mm. Conservation tillage treatments (MT and NT) significantly increased crop residue accumulation on the soil surface. Soil organic C, microbial biomass C and N, potential N mineralization, total N, and extractable P were highest in the surface layer of NT and decreased with depth. Soil organic C, microbial biomass C and N, total N and extractable P of plowed soil were generally more evenly distributed throughout the 0–150 mm depth. Potential N mineralization was closely associated with organic C and microbial biomass. Higher levels of soil organic C, microbial biomass C and N, potential N mineralization, total N, and extractable P were directly related to surface accumulation of crop residues promoted by conservation tillage management. Quality and productivity of soils could be maintained or improved with the use of conservation tillage.     

Effects of conventional tillage on biochemical properties of soils

Modification of soil environment by different farming practices can significantly affect crop growth. Tillage causes soil disturbance, altering the vertical distribution of soil organic matter and plant nutrient supplies in the soil surface, and it may affect the enzyme activity and microbial biomass which are responsible for transformation and cycling of organic matter and plant nutrients. In this study, the influence of three conventional tillage systems (shallow plowing, deep plowing and scarification) at different depths on the distribution and activity of enzymes, microbial biomass and nucleic acids in a cropped soil was investigated. Analysis of variance for depth and tillage showed the influence of the different tillage practices on the activity of some enzymes and on the nucleic acids. Glucosidase, galactosidase, nitrate reductase and dehydrogenase activity were significantly affected by the three tillage modalities. Activity in the upper layer (0–20 cm) was higher in the plots tilled by shallow plowing and scarification than in those tilled by deep plowing. Positive relationships were observed between the soil enzymes themselves, with the exception of urease and pyrophosphatase activity. Moreover, significant correlations were found between DNA and β-galactosidase, and between RNA and β-glucosidase, β-galactosidase, alkaline phosphatase and phosphodiesterase. α-Glucosidase, β-galactosidase, alkaline phosphatase and phosphodiesterase were highly correlated with biomass C determined by the fumigation-extraction method. Received: 27 June 1996     

Interactive effect of tillage depth and mulch on soil temperature, productivity and water use pattern of rainfed barley (Hordium vulgare L.)

Soil porosity and organic matter content influence the hydrology, thermal status and productivity of agricultural soils. Shape, size and continuity of soil pores are determined by tillage practices. Thus appropriate tillage and mulch management can conserve residual soil moisture during the post rainy season. This can play a key role in enhancing productivity under the rainfed ecosystem of subhumid region in eastern India. A field study was carried out on a fine loamy soil from 1993–1994 to 1995–1996. Two tillage treatments were conventional ploughing (150 mm depth) and shallow ploughing (90 mm) depth. Each tillage practice was tested with three mulch management viz., no mulch, soil dust mulch and rice (Oryza sativa L.) straw mulch. Soil organic carbon, bulk density, moisture retentivity, soil temperature with productivity and water use pattern of barley (Hordium vulgare L.) were measured.Reduction in ploughing depth resulted in nominal increase in profile (0.0–1.2 m) moisture status, yield, and soil thermal status at 14:00 and water use efficiency (WUE). However, it decreased the magnitude of soil temperature in the morning (07:00). Straw mulch conserved 19–21 mm of moisture in the profile (1.2 m) over the unmulched condition. Both soil dust and rice straw mulching elevated soil thermal status at 07:00 as compared to unmulched condition, but this trend was reversed at 14:00. Straw mulching significantly increased grain yield and WUE over soil dust mulch and unmulched condition. Impact of straw mulch was more pronounced under shallow ploughing depth. Shallow tillage with rice straw mulching is recommended to the farmers to obtain higher level of yield and water use efficiency.     

Urease activity in two cultivated and non-cultivated arid soils

Summary Since urease activity in soil is believed to be relatively constant, the present study was designed to examine the effects of incubation, soil depth and the effect of cultivation on the persistence of urease activity in arid soils. Two soils were used, a Harkey (coarse, silty, mixed, calcareous, thermic, Typic Torrifluvent) and a Saneli (Clayey over sandy skeletal, montmorillonitic, calcareous, Vertic Torrifluvent), each consisting of a cultivated field and a non-cultivated roadbed site. Urease activity was much lower and more varable in the roadbed soils (40 years without cultivation) than in the cultivated field soils. Pre-incubation for 24 h with urea (with toluene) and without urea (without toluene) greatly reduced the total urease activity in all cases in relation to cell free urease activity (with toluene). Urease activity in the two field soils decreased slightly with profile depth but the decrease was greatest below the plow depth (33 cm). Protease activity or some inactivation processes must have lowered the urease content since there was substantially reduced urease activity after most pre-incubations. The extent of the urease activity decrease was so great that the addition of urea would have been required to increase the production of urease enzyme.