A. Chakraborty

Fractionation and bioavailability of metals and their impacts on microbial properties in sewage irrigated soil

A study was conducted to evaluate the effect of long-term irrigation of sewage contaminated with heavy metals like Cd, Cr, Cu and Pb on microbial and biochemical parameters of soils of West Bengal, India. The microbial parameters included microbial biomass carbon (MBC), microbial metabolic quotient; the biochemical parameters included fluorescein diacetate hydrolyzing activity, beta-glucosidase, urease, phosphatase, and aryl sulphatase activities. A sequential extraction technique was used to quantify water soluble, exchangeable, carbonate bound, Fe/Mn-oxide bound, organically bound, and residual metal fractions. Metal concentrations in the two most labile fractions (i.e., water soluble and exchangeable fractions) were generally low. Total metal concentrations at each site seemed to be associated with soil amorphous Fe and Al minerals. The MBC and the enzymes studied were significantly and negatively correlated with water soluble and exchangeable metals but not significantly correlated with other forms, indicating that water soluble and exchangeable forms exerted a strong inhibitory effect on the soil microbial and biochemical parameters. It was concluded that irrigating soils with metal contaminated sewage seemed to damage soil quality in the long term.

Evaluation of MSW Compost as a Component of Integrated Nutrient Management in Wetland Rice

The potential of municipal solid waste compost (MSWC) was evaluated for rice cultivar, IET- 1444, during the wet seasons of 1997-99. Field experiments were conducted at the Agriculture Experimental Farm of Calcutta University, West Bengal, India using MSWC and cow dung manure (CDM), with or without urea (U), and fertilizers (F). Dry matter accumulation was highest with CDM + U, followed, in a descending order, by MSWC + U and F. Panicle length was largest and thousand–grain-weight were highest for F. Application of CDM alone gave 30% higher grain yield over MSWC but the latter, along with urea, increased grain yield by 49% over MSWC alone. Uptake of N by straw and grain was significantly higher with CDM as compared to MSWC. Percent N recovery was higher when fertilizer in the form of urea was applied with either CDM or MSWC. Uptake of heavy metals (Zn, Cu, and Pb) by straw and grain of rice was lower with the application of MSWC alone than with the other treatments except control. Uptake of Cd was below detection limit. There was no significant variation between the physico-chemical properties of soil due to the application of these treatments. Results indicated that MSWC application to rice was effective and safe to be used as an alternative organic supplement.

Effect of MSW Compost on Microbiological and Biochemical Soil Quality Indicators

This laboratory incubation study was conducted to evaluate the effect of municipal solid waste compost (MSWC) as a soil amendment on soil quality indicators, such as microbial biomass, and their activities. The MSWC was compared against cow dung manure (CDM), a traditional organic supplement. The comparative study was carried out in water regimes of 60% water holding capacity (WH) of soil and under waterlogged (WL) condition. MSWC was applied to an alluvial soil (Typic Fluvaquent) at the rates of 0, 2.5, 10, 20 and 40 and CDM at 0, 20 and 40 t/ha. Microbial biomass-C (MBC), glucose induced soil respiration (SR), urease and acid phosphatase activities in soil were analyzed following 15, 30, 45, 60, 90 and 120 days of incubation. The parameters studied were significantly higher in CDM-treated than in MSWC-treated soils. Increase in graded doses of MSWC from 2.5 to 40 t/ha substantially increased the MBC, SR, urease and phosphatase activities in the soil. In 60% WH regime, MBC and SR increased for the first 30 days of incubation and then declined. Under the WL regime, the MBC declined while SR increased from 15 days till 120 days of incubation. Urease and phosphatase activities of soil increased for up to 60 days during incubation in 60% WH regime and then decreased. Activities of both the enzymes under WL regime decreased progressively during incubation. There were no negative impacts on the soil quality indicators from high application rates of MSWC.

Butachlor Degradation in Tropical Soils: Effect of Application Rate, Biotic-Abiotic Interactions and Soil Conditions

The degradative characteristics of butachlor (N-Butoxymethyl-2-chloro-2′,6′-diethyla- cetanilide) were studied under controlled laboratory conditions in clay loam alluvial (AL) soil (Typic udifluvent) and coastal saline (CS) soil (Typic endoaquept) from rice cultivated fields. The application rates included field rate (FR), 2-times FR (2FR) and 10-times FR (10FR). The incubation study was carried out at 30°C with and without decomposed cow manure (DCM) at 60% of maximum water holding capacity (WHC) and waterlogged soil condition. The half-life values depended on the soil types and initial concentrations of butachlor. Butachlor degraded faster in AL soil and in soil amended with DCM under waterlogged condition. Microbial degradation is the major avenue of butachlor degradation from soils.

Influence of integrated plant nutrient supply system on soil quality restoration in a red and laterite soil: Einfluss integrierter pflanzennährstoff versorgung auf die wiederherstellun der bodenqualität von rotem und laterit boden

Unsuitable agricultural practices together with adverse environmental conditions have led to degradation of soil in many red and laterite zones of West Bengal, India. One method of recovering degraded soils in these regions is to add organic matter in order to improve soil characteristics, thereby enhancing biogeochemical nutrient cycles. The effect of organic and inorganic fertilizer amendments is often studied shortly after addition of a single dose to the soil, but less is known about the long-term effects of amendments. We conducted a study to determine the effects of the long-term addition of organic and inorganic fertilizer amendments either alone or in combination on soil physico-chemical and microbiological properties. Surface soil samples were taken from an experimental field site of the Regional Research Station, Bidhan Chandra Krishi Viswavidyalaya, Birbhum district, West Bengal, India in December 2000 after 2 years of experiment. Organic supplements (decomposed cow manure and vermicompost) either alone or in combination improved soil quality parameters such as water holding capacity, total organic C, microbial biomass C and soil respiration on comparison to chemical fertilizers and no input. Among the different treatment combinations, decomposed cow manure, along with chemical fertilizer gave significantly higher organic C (1.66%), microbial biomass C (289 μg/g oven dry soil) and substrate induced soil respiration (16.27 μg CO2/g oven dry soil/h) than the others. The results clearly indicate that the incorporation of organic supplements seemed to have a greater positive effect on the soil characteristics studied and is beneficial for recovering degraded soils.

Effect of composting on extractability and relative availability of heavy metals present in Calcutta municipal solid waste

How composting affects heavy metal content is largely unknown. Accordingly, we investigate the total content of six heavy metals, Cd/Zn ratio and the Zn-equiv, the relative availability and fractionation study to assess the suitability of compost derived out of those for environmental concerns. During composting, total metal content increased but their RA decreased. As a result of composting bioavailable form of metals also decreased. High significant correlations between different forms of heavy metals content and degree of humification were found for all the elements. Composting increases humic acid content than fulvic acid. This transformation is mainly responsible to serve as binding agent for metal thereby moderating the rapid metal mobilization.

Assessment of the impact of pesticide residues on microbiological and biochemical parameters of tea garden soils in India

The main aim of this study was to assess the impact of pesticidal residues on soil microbial and biochemical parameters of the tea garden soils. The microbial biomass carbon (MBC), basal (BSR) and substrate induced respirations (SIR), β -glucosidase activity and fluorescein diacetate hydrolyzing activity (FDHA) of six tea garden soils, along with two adjacent forest soils (control) in West Bengal, India were measured. The biomass and its activities and biochemical parameters were generally lower in the tea garden soils than the control soils. The MBC of the soils ranged from 295.5 to 767.5 μ g g− 1. The BSR and SIR ranged from 1.65 to 3.08 μ g CO2-C g− 1 soil h− 1 and 3.08 to 10.76 μ g CO2-C g− 1h− 1 respectively. The β -glucosidase and FDHA of the soils varied from 33.3 and 76.3 μ g para-nitrophenol g− 1 soil h− 1 and 60.5 to 173.5 μ g fluorescein g− 1h− 1respectively. The tea garden soils contained variable residues of organophosphorus and organochlorine pesticides, which negatively affected the MBC, BSR, SIR, FDHA and β -glucosidase activity. Ethion and chlorpyriphos pesticide residues in all the tea garden soils varied from 5.00 to 527.8 ppb and 17.6 to 478.1 ppb respectively. The α endosulfan, β endosulfan and endosulfan sulfate pesticide residues in the tea garden soils ranged from 7.40 to 81.40 ppb, 8.50 to 256.1 ppb and 55 to 95.9 ppb respectively. Canonical correlation analysis shows that 93% of the total variation was associated with the negative impact of chlorpyriphos, β and α endosulfan and endosulfan sulfate on MBC, BSR and FDHA. At the same time ethion had negative impact on SIR and β -glucosidase. Data demonstrated that the pesticide residues had a strong impact on the microbial and biochemical components of soil quality.

Study on the efficacy of some bio resources as mulch for soil moisture conservation and yield of rain fed groundnut ( Arachis hypogaea )

A two-year field experiment was conducted to study the efficacy of some mulching materials for soil moisture conservation and yield of groundnut (Arachis hypogaea) in summer under rainfed conditions. The mulches used were water hyacinth (WH), rice straw (RS), banana leaves covered with grass (BL), jute stick (JS) and white polythene sheet (PS). The groundnut cultivar AK-12-24 was sown by flat and ridge planting methods. The WH mulch conserved more soil moisture than the other mulches. The soil temperature at the root zone depth was also reduced with the use of WH mulch. The mulches used and the planting methods did not significantly affect the number of leaves and branches per plant. The mulches WH and RS manifested higher kernel yields of 0.67 and 0.61 t ha − 1 respectively. The soil moisture content with ridge planting method was 8.4%, significantly higher than the flat planting method (7.3%). Soil temperature with flat (33.7°C) and ridge (33.2°C) planting method were statistically similar. The ridge method of planting produced higher kernel yield of groundnut (0.57 t ha − 1) than flat planting (0.42 t ha − 1).

Influence of soil properties on urease activity under different agro-ecosystems

Urease activity (by buffer and non-buffer method) of soils of different agro-ecosystems in alluvial soil was studied. Urease activity by buffer method records a higher value than the non-buffer method. Both the methods showed significant positive correlation (0.99**) between each other. Urease activity by both methods showed positive correlation with organic matter (0.88** and 0.89**, buffer method) and clay content (0.91** and 0.83*, non-buffer method)) of the soils. Multiple regression analysis showed that the stabilization of urease activity in the soils studied was due to an organic matter – enzyme complex. Among the organic matter humus C plays a dominating role to control the urease activity of the soils.

Physico-Chemical properties, heavy metals and their relations in cultivated landfill soils dumped with municipal solid wastes

Long-term fate and behaviour of heavy metals in soil, treated with composted-municipal solid wastes (MSW), are largely unknown. Accordingly, we investigated some physico-chemical properties, the relative availability (RA) of heavy metals and Cd/Zn ratio in soils of a century old cultivated landfill site dumped with Calcutta-MSW during monsoon, winter and summer seasons of 1999-2001. This was done to assess the suitability of compost derived out of those for environmental concerns. The electrical conductivity (EC), total nitrogen (N), available phosphorus (P), carbonate content of soils were significantly highest in summer. The landfill soils recorded higher EC, organic-C, total N, available P, carbonate, and total, diphenyl triamine penta acetic acid (DTPA) and water-soluble heavy metals (Zn, Cu, Pb and Cd) including the RA, than the normal agricultural alluvial soil (ALV). Among the heavy-metals studied, the RA of Cu was more. The Cd/Zn ratio of the landfill soils ranged from 1.74-2.94% as against ALV (0.5%). The heavy metals species of the landfill soils were negatively correlated with the physico-chemical properties, and the coefficients were generally statistically significant, with the bioavailable forms (DTPA and water-soluble) in most cases. Data indicated the risk factors, involved in the long-term use of composted-MSW in soil.