Artificial neural networks for predicting unsaturated soil hydraulic characteristics at different applied tensions

Direct measurement of unsaturated hydraulic parameters that are crucial inputs in any modeling of water flow or solute transport through the vadose zone is costly and time-consuming. Therefore, indirect methods like artificial neural networks (ANNs) can be used to estimate these parameters. Different ANNs conditions [two training algorithms (Trainlm and Traingd), two transfer functions (Tansig and Logsig), and different combinations of the input variables sand, silt, clay, bulk density (BD), soil organic matter (SOM) and initial (?_i) and saturated (?_s) volumetric water content] were used to predict the unsaturated hydraulic conductivity, K _ψ [at six applied tensions (ψ) of 0–0.2 m] and sorptive number, α (at five ψ values of 0.03–0.2 m) that correspond to 138 soil samples from two neighboring study areas located in the Agricultural College, Shiraz University, Islamic Republic of Iran. A four-layer ANNs with three and four nodes in the hidden layers, performed the best in predicting K _ψ and α. Traingd produced the best predictions over all input variables when Tansig and Logsig transfer functions were used for K _ψ and α at different values of ψ, respectively. ‘Silt + clay + sand + BD + SOM’ was the most basic influential input variable for predictions of K _ψ and α at almost all values of ψ. The accuracy of ANNs-predicted K _ψ decreased with decreasing ψ from 0.2 to 0.1 m, followed by an increase to a ψ value of 0 m; a specific relationship was not observed for α. Therefore, ANNs can be used to predict K _ψ with greater confidence at moderate values of ψ than at lower or higher values. The normalized root mean square error, NRMSE, confirmed that ANNs predictions for K _ψ were more accurate than predictions for α. Because reliable predictions were obtained for K _ψ, and to a lesser extent for α, it is recommended that such intelligence models are used to predict these vital soil hydraulic attributes.     

Determination of unsaturated soil hydraulic properties at different applied tensions and water qualities

Irrigation with low-quality water may change soil hydraulic properties due to excessive electrical conductivity (EC_w) and sodium adsorption ratio (SAR_w). Field experiments were conducted to determine the effects of water quality (EC_w of 0.5–20 dS m^?1 and SAR_w of 0.5–40 mol^0.5 l^?0.5) on the hydraulic properties of a sandy clay loam soil (containing ～421 g gravel kg^?1 soil) at applied tensions of 0–0.2 m. The mean unsaturated hydraulic conductivity [K(ψ)], sorptive number (α) and sorptivity coefficient (S) varied with change in EC_w and SAR_w as quadratic or power equations, whereas macroscopic capillary length, λ, varied as quadratic or logarithmic equations. The maximum value of K(ψ) was obtained with a EC_w/SAR_w of 10 dS m^?1/20 mol^0.5 l^?0.5 at tensions of 0.2 and 0.15 m, and with 10 dS m^?1/10 mol^0.5 l^?0.5 at other tensions. Changes in K(ψ) due to the application of EC_w and SAR_w decreased as applied tension increased. Analysis indicated that 13.7 and 86.3% of water flow corresponded to soil pore diameters <1.5 and >1.5 μm, respectively, confirming that macropores are dominant in the studied soil. The findings indicated that use of saline waters with an EC of <10 dS m^?1 can improve soil hydraulic properties in such soils. Irrigation waters with SAR_w < 20 mol^0.5 l^?0.5 may not adversely affect hydraulic attributes at early time; although higher SAR_w may negatively affect them.     

In situ characterization of hydraulic conductivities of individual soil profile layers during infiltration over long time periods

Several studies have raised serious doubts about the suitability of small cores for measuring water‐movement attributes, due to their potential to provide unrealistic representation of macropore connectivity and abundance. This study explored the potential of lysimeter‐scale experiments to calculate the hydraulic conductivity, K(ψ_m), of undisturbed soil layers in a matric potential (ψ_m) range between 0 and −4 kPa. Four large lysimeters were collected from a Dystric Cambisol. For each lysimeter a tension infiltrometer supplied infiltrating water under suctions of 0, 0.5, 1 and 1.5 kPa. Soil water dynamics were measured in situ using arrays of tensiometers, at depths corresponding with layer boundaries. The results show clearly that infiltration and drainage rates are intimately linked to temporal ψ_m dynamics, which themselves are determined by preferential flow and soil‐layer interactions. A quasi‐steady state was identified as when infiltration matched drainage, and ψ_m measurements showed each layer had a stable hydraulic gradient, which then allowed in situ determination of the K(ψ_m) relationship of individual soil layers. For this soil K(ψ_m) is distinctly different for each soil layer, and these differences are consistent among the four lysimeters. A consistent feature is that all layers have a distinct change in the slope of the K(ψ_m) relationship, in the ψ_m range of −0.5 to −1.5 kPa, highlighting a dual‐porosity character. The whole‐column infiltration behaviour was strongly linked to the K(ψ_m) relationship of the surface layer (0–2 cm depth), and therefore hydraulic characterization of this layer should be a critical component of a soil survey.     

Spatial variability of water retention parameters and saturated hydraulic conductivity in a calcareous Inceptisols (Khuzestan province of Iran) under sugarcane cropping

The objective of this study was to quantify inherent spatial variability and spatial cross-correlation of the van Genuchten retention parameters and saturated hydraulic conductivity (K_s) of surface and subsurface layers in a calcareous Inceptisols (Khuzestan province, Iran) under sugarcane cropping. Measurements were performed on 100-cm³ undisturbed soil cores collected at 94 locations along a 30-m-long transect with horizontal sampling distance intervals of 0.3 and 1 m at soil depths of 0–40 and 40–80 cm, respectively. Spatial variability was investigated using conventional statistics and geostatistical techniques. Coefficient of variation (CV) varied from 8.2% (for shape parameter, n at 40–80 cm depth) to 256.7% (for K_s at 0–40 cm depth). The n parameter and saturated water content, θ_s, showed a small-scale spatial heterogeneity with a maximum CV of 11.3% for the first depth and 9.2% for the second depth. Most of the hydraulic parameters at both depths showed a spatial structure and convex experimental semivariograms with dominant spherical models with the influence range of 3.2–41 m. In most cases, the extent of spatial correlation scales of cross-semivariograms for pairs of cross-correlated hydraulic variables was found to be different with reference to those relating to the direct semivariograms of correlated variables.     

Effects of a bentonite–water mixture on soil-saturated hydraulic conductivity

To reduce water loss in light-textured soils, hydraulic conductivity should be reduced by mixing the soils with some soil conditioners, e.g. sodium-bentonite. The objectives of this study were to investigate the effects of irrigation water with different bentonite concentrations (0, 0.05, 0.1, 0.15 and 0.2%) on hydraulic gradient (i) and relative saturated hydraulic conductivity (K _rs) in a laboratory soil column with a loamy sand soil. Addition of sodium-bentonite to the soil increased i throughout each experiment. Furthermore, addition of bentonite reduced K _rs, and a 0.2% bentonite–water concentration after infiltration of 48 mm of bentonite–water mixture (BWM), reduced the K _rs value to 56% of K _s. K _rs was reduced as the concentrations of bentonite increased and its value reached ～0.5 to 0.6 as the infiltration of BWM increased. The lowest value of K _rs and the greatest reduction rate occurred at a bentonite concentration of 0.2%. It is concluded that BWM can be used as a channel liner. Using a 0.2% bentonite concentration resulted in a reduction in the seepage ratio from 1.0 to 0.08.     

Application of two methods to determine hydraulic conductivity with disc permeameters on sloping land

The purpose of the present study was to compare two methods for estimating the hydraulic conductivity near saturation with disc permeameters, and to identify their merits when studying runoff on sloping land. The soil's hydraulic conductivity (K) was measured with disc permeameters at a sequence of nominal pressures (ψ) in three blocks with average slope gradients of 11.0% (two occasions), 21.5% (two occasions) and 29.3% (one occasion), respectively, within a sloping area, 40 m wide and 100 m long. Two different methods were used. In the first, the split‐location method, the permeameter was moved to an adjacent spot after measurement at each applied ψ. The estimate of K(ψ) was based on measured sorptivity, steady‐state volumetric flow, initial volumetric water content and the volumetric water content at the applied ψ. In the second method, the one‐location method, the permeameter was not moved during the measurements at each sequence of applied ψ and the estimate of K(ψ) was based only on steady‐state volumetric flow and piece‐wise application of the exponential relation between K and ψ. The latter method generally gave smaller estimates of K than the former on the gentle slopes. These differences were smaller or negligible on steeper slopes. The slope gradient and the conditions in the uppermost soil layers had a definite influence on the values of K obtained. The one‐location method is recommended in studies in which disturbance of the soil surface must be kept to a minimum, as is the case in experimental plots.     

Simple methods for estimating field capacity using Mamdani inference system and regression tree

Using easily measurable soil properties could save time and cost for field capacity (FC) prediction. The objective of this study was to compare Mamdani fuzzy inference system (MFIS) and regression tree (RT) for FC predicting using such properties. One hundred and sixty-five soil samples from Unsaturated Soil hydraulic database data-set and 45 from Hydraulic Properties of European Soils data-set were used for the development and validation of MFIS and RT, respectively. Fuzzy rules and tree diagram based on the relationships between these predictor variables and the response variable FC were defined and 48 rules were written. Results showed a positive linear relevancy in terms of standardized independent variable weight, W*, between clay content and FC and negative linear relevancy between geometric mean particular size diameter (d_g) and FC. Among predictor variables, d_g (W* = 0.81) and bulk density (BD) (W* = 0.49) had the highest and lowest influence on FC, respectively. A tree diagram is presented for the prediction of FC using clay content, dg, and BD. Overall, based on statistical parameters, RT method (R² = 0.78, geometric mean error (GME) = 1.02, mean error (ME) = 0.01 cm³ cm^?3, and root mean square error (RMSE) = 0.04 cm³ cm^?3) showed a higher performance than MFIS method (R² = 0.72, GME = 1.16, ME = 0.08 cm³ cm^?3, and RMSE = 0.06 cm³ cm^?3) to predict FC.     

Pedo-transfer functions for estimating the hydraulic properties of paddy soils in subtropical central China

Pedo-transfer functions (PTFs) have been widely used to estimate soil hydraulic properties in the simulation of catchment eco-hydrological processes. However, the accuracy of existing PTFs is usually inadequate for use. To develop PTFs for local use, soil columns were collected from a double rice-cropped agricultural catchment in subtropical central China. The PTFs for saturated soil hydraulic conductivity (K_s) and parameters (θ_s, α, and n) of the van Genuchten model for the soil water retention curve (SWRC) were obtained based on soil’s basic properties, and compared with models developed by Li et al. in 2007 and Wösten et al. in 1999, respectively. Our results indicated that K_s in the range of 0.04–1087 cm d^?1 and θ_s in the range of 0.34–0.51 cm³ cm^?3 were both well estimated with the R²_adj of 0.72 and 0.87, respectively, but α (0.04–0.65 cm^?1) and n (1.05–1.21) were relatively poorly predicted with the respective R²_adj of 0.38 and 0.55, despite the use of more input parameters. Our local derived PTFs outperformed the other two existing models. However, if the local PTFs for paddy soils are not available, the Wösten et al. 1999 model can be proposed as a useful alternative. Therefore, this study can improve our understanding of the development and application of PTFs for predicting paddy soil hydraulic properties in China.     

Assessment of variation in drought tolerance using some key physiological criteria in potential wheat (Triticum aestivum L.) cultivars of different geographic origins

The present experiment comprised seven wheat cultivars, two drought levels (0 and 17% PEG-8000) and four replicates. The seeds of six wheat cultivars (Al-lugaimi, Bonus, Kronos, Yecora-rojo, Irena and Sama) were supplied by the King Saud University, Riyaz, Saudi Arabia, whereas S-24 was obtained from the Department of Botany, University of Agriculture, Faisalabad. The seeds were allowed to germinate and grow for 20 days in medium having full-strength Hoagland's nutrient solution or Hoagland's solution with 17% PEG-8000. For the appraisal of drought tolerance, various physiological traits such as gas-exchange attributes (A, E, C_i, g_s , and A/E), leaf water relations (ψ_w, ψ_s and ψ_p) and the activities of key antioxidant enzymes (SOD, POD and CAT) were determined. On the basis of biomass and gas-exchange attributes (A, E, and g_s ), cultivars Al-lugaimi and Sama were found to be drought tolerant, cultivars Yecora-rojo and Irena moderately drought tolerant, and cultivars S-24, Bonus and Kronos drought sensitive. However, plant osmotic adjustment and the activities of potential antioxidant enzymes (SOD, POD and CAT) were not found to be associated with drought tolerance of the different wheat cultivars.     

Effect of zeolite and saline water application on saturated hydraulic conductivity and infiltration in different soil textures

The effects of zeolite application (0, 4, 8 and16 g kg^?1) and saline water (0.5, 1.5, 3.0 and 5.0 dS m^?1) on saturated hydraulic conductivity (K _s) and sorptivity (S) in different soils were evaluated under laboratory conditions. Results showed that K _s was increased at salinity levels of 0.5‐1.5 dS m^?1 in clay loam and loam with 8 and 4 g zeolite kg^?1 soil, respectively, and at salinity levels of 3.0–5.0 dS m^?1 with 16 g zeolite kg^?1 soil. K _s was decreased by using low and high salinity levels in sandy loam with application of 8 and 16 g zeolite kg^?1, respectively. In clay loam, salinity levels of 0.5–3.0 dS m^?1 with application of 16 g kg^?1 zeolite and 5.0 dS m^?1 with application of 8 g zeolite kg^?1 soil resulted in the lowest values of S. In loam, all salinity levels with application of 16 g zeolite kg^?1 soil increased S compared with other zeolite application rates. In sandy loam, only a salinity level of 0.5 dS m^?1 with application of 4 g zeolite kg^?1 soil increased S. Other zeolite applications decreased S, whereas increasing the zeolite application to 16 g kg^?1 soil resulted in the lowest value of S.     

Evaluation of the spatial pattern of surface soil water content of a karst hillslope in Southwest China using a state-space approach

This study aims to evaluate the effects of soil physicochemical properties and environmental factors on the spatial patterns of surface soil water content (SWC) based on the state-space approach and linear regression analysis. For this purpose, based on a grid sampling scheme (10 m × 10 m) applied to a 90 m × 120 m plot located on a karst hillslope of Southwest China, the SWC at 0–16 cm depth was measured 3 times across 130 sampling points, and soil texture, bulk density (BD), saturated hydraulic conductivity (K_s), organic carbon (SOC), and rock fragment content as well as site elevation (SE) were also measured at these locations. Results showed that the distribution pattern of SWC could be more successfully predicted by the first-order state-space models (R² = 67.5–99.9% and RMSE = 0.01–0.14) than the classic linear regression models (R² = 10.8–79.3% and RMSE = 0.11–0.24). The input combination containing silt content (Silt), K_s, and SOC produced the best state-space model, explaining 99.9% of the variation in SWC. And Silt was identified as the first-order controlling factor that explained 98.7% of the variation. In contrast, the best linear regression model using all of the variables only explained 79.3% of variation.     

Response of nectarines to organic fertilization under the rain-fed ecosystem of Northwest Himalayas

The comparative efficacy of organic sources on cropping behavior, nutrient dynamics, physico-chemical and biological properties of soil and fruit quality under rain-fed agroecosystem on “Silver King” nectarines was investigated. Bio-organic nutrients, namely vermi-compost (VC), biofertilizer (BF), farmyard manure (FYM), compost (comp), vermiwash (VW) and cow urine (CU) were evaluated in 11 different treatment combinations. The treatment application of VC at 25 kg tree^?1, BF at 40 g tree^?1, FYM at 30 kg tree^?1, comp at 15 kg tree^?1, VW_1:10 and CU_1:10 significantly improved plant growth and fruit quality characteristics of nectarine trees. This superior combination also enhanced physico-chemical and biological properties of the rhizosphere soil when compared to control as conventional chemical fertilizer application nitrogen, phosphorus and potassium (NPK) fertilizers. Different treatments of bio-organic sources changed pH of the soil to neutral. Available macronutrient contents of soil (viz. N, P, and K) increased by 57.8%, 27.7%, and 16.4%, respectively. Microbial biomass of soil fungi, total bacteria, actinobacteria, and arbuscular mycorrhizal fungi improved 66.0%, 73.8%, 133.3% and 350.0%, respectively, over control. Considerably, a higher amount of leaf macronutrients, N (3.53%), P (0.23%), and K (3.2%), was also recorded over control.     

Behavior of iodine in a forest plot,an upland field and a paddy field in the upland area of Tsukuba,Japan: Seasonal variations in iodine concentration in precipitation and soil water and estimation of the annual iodine accumulative amount in soil horizons

Abstract

In the course of a series of studies conducted to investigate the long-term behavior of ¹²⁹I (which has a half-life of 16 million years) in the environment, seasonal variation in the concentration of stable iodine (¹²⁷I) in precipitation and soil water to a depth of 2.5 m in a forest plot, an upland field and a paddy field in the upland area of Tsukuba, Japan, were determined. Iodine concentration in precipitation tended to increase during the summer (high air temperature) season and low-rainfall period, and a positive high correlation was observed between annual rainfall and the annual amount of iodine supplied by precipitation. No seasonal variations in iodine concentration in soil water were observed at any depth in the forest plot and upland field unlike at shallow depths (0.2 and 0.5 m) in the paddy field. In the paddy field, from the beginning of summer irrigation, under flooding conditions, iodine concentration in soil water at shallow depths (0.2 and 0.5 m) continuously increased, and immediately before mid-summer (intermittent) drainage and drainage, the maximum iodine concentration (approximately 50 µg L^?1) and lowest E_h values (approximately ?150 to ?200 mV) were recorded. These high iodine concentration levels and low E_h values were ascribed to high air temperature (approximately > 25°C on average every 10 days) and the continuation of the groundwater level above the ground surface. As for the temporary winter irrigation period (mean daily air temperature 2?4°C), the iodine concentration was low (1.7–3.7 µg L^?1) at all depths, as was the case in the non-irrigation period. After mid-summer drainage, and drainage, the iodine concentration in soil water at depths of 0.2 and 0.5 m decreased drastically as the groundwater level decreased. The mean annual amount of iodine accumulated in the surface soil horizons (0–0.67 m) in the forest plot was estimated to be approximately 2.9 mg m^?2 (7.5 µg kg^?1 dry soil), which coincided with the mean annual amount of iodine supplied to the earth surface by precipitation. A mildly oxidative subsurface 2Bw horizon (0.60–0.89 m) in the paddy field was estimated to illuviate approximately 3.1 mg m^?2 (20 µg kg^?1 dry soil) of iodine annually by retaining iodine in the soil water percolated to this horizon.     

Low-molecular weight organic acids improve plant availability of phosphorus in different textured calcareous soils

Understanding the role of organic acids on phosphorus (P) sorption capacity of soils is very important for its economic and friendly management. Combining P application with low-molecular weight organic acids could result in its higher plant availability for prolonged time. Therefore, citric and oxalic acid (at the rate of 1.0 mM kg^?1 soil) were evaluated for their effect on P sorption capacity and its plant availability in two different textured calcareous soils. Organic acids decreased P sorption capacity and organic carbon partition coefficient (K_oc) whereas increased Gibbs free energy (ΔG) of P. Organic-acid-treated soils required lesser quantity of P fertilizer to produce soil solution P concentration optimum for plant growth (external P requirement [EPR_0.2]), that is, 0.2 mg L^?1. Citric acid was efficient than oxalic acid in the above effects. P sorption parameters of Freundlich model were negatively correlated with lime potential and ΔG whereas had positive correlation (P < 0.05) with EPR_0.2 and K_oc. Incubation with oxalic acid increased available P in loamy sand and loam soil by 20% and 30%, respectively. Thus, organic acids could help reduce application rate of P fertilizer through lowering its adsorption in highly P-fixing soils without compromise on yield.     

Effects of conocarpus biochar on hydraulic properties of calcareous sandy soil: influence of particle size and application depth

A laboratory column experiment was conducted to investigate the effects of 400°C biochar at application rate of 15 g kg^?1 (21.9 t ha^?1) with different particle sizes (<0.5 mm (S₁), 0.5–1 mm (S₂) and 1–2 mm (S₃)) and application depths (0–2 cm depth (D₀), 4–6 cm depth (D₅) and 8–10 cm depth (D₁₀)) on hydro-physical properties of sandy loam soil. The results indicated that applying biochar decreased the waterfront and saturated hydraulic conductivity of sandy loam soil. The cumulative evaporation was the highest and amounted to 40.9 mm in the non-treated soil, but it recorded the lowest amount of 32.2–35.5 mm in the biochar-treated soil. Applying biochar caused significant increases in the amount of conserved and retained water with the highest amount of water conserved in soil treated with S₂ biochar at D₅. Moreover, the cumulative water infiltration through the soil was significantly reduced by S₁ and S₂ biochars at D₀. The values of saturated hydraulic conductivity for biochar treatments were significantly lower than those for the control, with the lowest values for S₁ at D₀ and D₅. These results suggest positive improvement for the hydro-properties of coarse-textured soils following biochar addition, especially with finer particles of biochar.     

Effect of biochar application rate on soil physical and hydraulic properties of a sandy loam

Biochar is used as a soil amendment for improving soil quality and enhancing carbon sequestration. In this study, a loamy sand soil was amended at different rates (0%, 25%, 50%, 75%, and 100% v/v) of biochar, and its physical and hydraulic properties were analyzed, including particle density, bulk density, porosity, infiltration, saturated hydraulic conductivity, and volumetric water content. The wilting rate of tomato (Solanum lycopersicum) grown in soil amended with various levels of biochar was evaluated on a scale of 0–10. Statistical analyses were conducted using linear regression. The results showed that bulk density decreased linearly (R² = 0.997) from 1.325 to 0.363 g cm^?3 while the particle density decreased (R² = 0.915) from 2.65 to 1.60 g cm^?3 with increased biochar amendment, with porosity increasing (R² = 0.994) from 0.500 to 0.773 cm³ cm^?3. The mean volumetric water content ranged from 3.90 to 14.00 cm³ cm^?3, while the wilting rate of tomato ranged from 4.67 to 9.50, respectively, for the non-amended soil and 100% biochar-amended soil. These results strongly suggest positive improvement of soil physical and hydraulic properties following addition of biochar amendment.     

Surface soil hydraulic properties in four soil series under different land uses and their temporal changes

The concepts of “genoform” and “phenoform” distinguish the genetically-defined soil series and the variation of soil properties resulted from different land uses and management practices. With the repeated field measurements over time, we attempted to understand the difference of soil hydraulic properties among different land uses for a given soil series, and their temporal dynamics. Four soil series (Glenelg, Hagerstown, Joanna, and Morrison) in Pennsylvania with contrasting textures, structures, and parent materials were investigated. Within each soil series, four common land uses (woodland, cropland, pasture, and urban) were examined. At each site of soil series–land use combination, field-saturated and near-saturated hydraulic conductivities, K(ψ), were measured at the soil surface using standard tension infiltrometers at water supply potentials (ψ) of − 0.12, − .06, − 0.03, − 0.02, − 0.01, and 0 m. Surface infiltration measurements were repeated at each site in May and October from 2004 to 2006. The analysis of variance indicated that the measurement time (May or October) had the greatest impact on all measured hydraulic conductivities (p < 0.001), followed by the land use (p < 0.05 for K_ψ = 0 and K_{ψ = − 0.06}) and soil series (p < 0.06 for K_{ψ = − 0.01} to K_{ψ = − 0.03}). The interactions between the time and land use and between the soil series and land use were statistically significant for K_ψ = 0 and K_{ψ = − 0.01.} When separated by the measurement time, land use showed greater impacts in October than in May, while soil series had greater impacts in May than in October. Among the four land uses, woodland showed less obvious temporal change compared to the other three land uses because of less human-induced impacts and more consistent ground cover. Other three land uses generally showed a higher hydraulic conductivity in May than in October due to the drier initial soil moisture condition and related management practices in the spring that gave rise to more significant macropore flow. The results suggested that the initial soil moisture is an important variable that drives the temporal variation of the surface soil hydraulic properties.     

Effect of long-term organic and mineral fertilizer on physical properties in root zone of a clayey Ultisol

To explore the effects of long-term organic and mineral fertilization practices on the physical properties in Ultisol of south China, a study was conducted since 1998 to investigate the effects of a control (CK), application of chemical fertilizers (NPK), application of organic manure (OM), and NPK fertilizer plus straw returning (NPK + straw). Results showed that OM significantly increased soil water retention capacity at all tensions but with larger increment in low tension at depths of 0–10 cm and 10–20 cm (p < 0.05) when compared with the CK. On the contrary, NPK and NPK + straw led to a decrease in soil water retention capacity under chemical treatments. In the field both in wet and dry periods, soil water content was significantly higher in OM than in NPK + straw and NPK (p < 0.05) since soil hydraulic conductivity (saturated and unsaturated) are lower in OM than in other treatments (p < 0.05). OM was also found to have the lowest soil bulk density and penetration resistance of the four treatments. A high negative correlation was observed between the soil organic carbon and the bulk density and the penetration resistance (p < 0.01). In this way, the application of OM improved the clayey soil physical properties.     

Improving soil organic carbon pools through inclusion of summer mungbean in cereal-cereal cropping systems in Indo-Gangetic plain

Long-term effect of mungbean inclusion in lowland rice-wheat and upland maize-wheat systems on soil carbon (C) pools, particulate organic C (POC), and C-stabilization was envisaged in organic, inorganic and without nutrient management practices. In both lowland and upland systems, mungbean inclusion increased very-labile C (Cfrac₁) and labile C (Cfrac₂) in surface soil (0–0.2 m). Mungbean inclusion in cereal-cereal cropping systems improved POC, being higher in lowland (107.4%). Lowland rice-based system had higher passive C-pool (11.1 Mg C ha^?1) over upland maize-based system (6.6 Mg C ha^?1) indicating that rice ecology facilitates the stabilization of passive C-pool, which has longer persistence in soil. Organic nutrient management (farmyard manure + full crop residue + biofertilizers) increased Cfrac₁ and carbon management index (CMI) over inorganic treatment. In surface soil, higher CMI values were evident in mungbean included cropping systems in both lowland and upland conditions. Mungbean inclusion increased grain yield of cereal crops, and yield improvement followed the order of maize (23.7–31.3%) > rice (16.9–27.0%) > wheat (lowland 7.0–10.7%; upland 5.4–16.6%). Thus, the inclusion of summer mungbean in cereal-cereal cropping systems could be a long-term strategy to enrich soil organic C and to ensure sustainability of cereal-cereal cropping systems.     

Bioaccumulation and toxicity of lead,influenced by edaphic factors: using earthworms to study the effect of Pb on ecological health

Purpose

Lead (Pb) is a highly studied contaminant with no known biological function that causes harmful adverse effects on ecological and human health. We tried to evaluate how protective the current soil regulatory levels are for Pb towards safeguarding the ecological health. In order to achieve this, our study evaluated the effect of soil texture and pH on the toxicity and availability of lead to earthworms in soils varying in soil properties.

Materials and methods

The earthworm Eisenia fetida was exposed to Pb in three soils with different physico-chemical characteristics. Pb solutions were homogenously mixed with soil to obtain concentrations ranging from 0 to 10,000 mg/kg Pb dry soil. Avoidance behaviour, weight loss and mortality were measured in this study to calculate the EC₅₀ and LC₅₀ values.

Results and discussion

Weight loss and mortality in earthworms due to Pb toxicity were in the following order: acidic > neutral > alkaline soil. The EC₅₀ values resulting in 50% decrease in worm weight over control for Pb in acidic, neutral and alkaline soils were 460, 3606 and 5753 mg/kg soil, respectively. Thus, the acidic soil recorded an EC₅₀ well below the soil guideline value for Pb. Whereas, the LC₅₀ values resulting in 50% mortality in worms over control were 1161, 4648 and 7851 mg/kg, respectively, for acidic, neutral and alkaline soils. The Pb concentrations in earthworms ranged from 0.2 to 740 mg/kg wet weight. Soils with low clay content and acidic to neutral pH values demonstrated an increased Pb toxicity in earthworms compared to the soils with alkaline pH.

Conclusions

The worm weight loss is a more sensitive parameter than the mortality. This study emphasizes that the soil regulatory levels for Pb are not protective of worms in acidic soils. Therefore, care should be taken when using the current regulatory limits to assess and predict the safety of a contaminated site with acidic soils towards the ecological health.