Muneshwar Singh

Sorption characteristics of lead and cadmium in some soils of India

To evaluate the sorption mechanism of heavy metals viz. cadmium (Cd) and lead (Pb) in major soil types, an experiment was conducted on Vertic Ustochrept, Typic Eutrochrept, Typic Ustipsamment, Typic Haplustalf and Typic Ustorthent representing five agroecological zones (AEZ) of India. The thermodynamic parameters viz. K°, ΔG°, ΔH° and ΔS° were determined by using sorption data and concentrations of Cd and Pb in equilibrium solution at two different temperatures 25±2 and 45±2 °C of soil suspension. Results showed that the data of heavy metals sorption could be described satisfactorily by Freundlich and modified (two surfaces) Langmuir isotherms. The Pb sorption was maximum in the order of Vertic Ustochrept>Typic Eutrochrept>Typic Ustochrept>Typic Haplustalf>Typic Ustorthent. The magnitude of Cd sorption was 4 to 6 times less than that of Pb. The Vertic Ustochrept sorbed Cd 4.0 and 2.5 times and Pb by 2.0 and 1.9 times more than that of Ustorthent and Haplustalf soils, respectively. Such variations in Cd and Pb sorption maxima were correlated with the differences in pH, CEC and organic matter content of the soils. Thermodynamic parameters revealed that heavy metal sorption increased as the value of K°, ΔG°, ΔH° and ΔS° increased with temperature. The high values of ΔG° both for Pb and Cd indicated that both the reactions are spontaneous. The values of ΔH° were found to be negative for Cd and positive for Pb concluded that Cd sorption reaction was exothermic while Pb sorption was found to be an endothermic reaction in all the soils.

Effects of farmyard manure and phosphorus on zinc transformations and phyto-availability in two alfisols of India

Laboratory pot experiments were run to study the effects of added zinc (Zn) with and without farmyard manure (FYM) and phosphorus (P) on Zn transformations in two Alfisols, together with Zn uptake by wheat plants grown up to 60 days. In the first experiment the treatments included four levels of Zn (0, 3.75, 7.5 and 15 mgkg(-1) soil) and two levels of FYM (0 and 10 tha(-1)), and in the second experiment five levels of P (0, 20, 40, 80 and 160 mgkg(-1) soil) and one level of Zn (7.5 mgkg(-1) soil). The soils were sequentially fractionated into water-soluble plus exchangeable (CA-Zn), inorganically bound (AAC-Zn), organically bound (PYR-Zn), oxide bound (OX-Zn) and residual (RES-Zn) forms. The effect of added FYM was more evident on the OX-Zn fraction and the percentage utilization of Zn by wheat was the greatest with the addition of FYM alone at the rate of 10 tha(-1) (1.95-2.38%) in comparison to other treatment combinations. Among the levels, application of 7.5 mg Zn kg(-1) soil showed the maximum increase in different fractions of soil Zn and significantly increased the Zn utilization by wheat (0.87-1.17%) as compared to other Zn levels (0.58-0.88%). On an average, about 85% of the added Zn was recovered in different fractions in Zn treated pots. However, the recovery per cent of the added Zn was significantly higher at Zn level 7.5 (95%) mgkg(-1) soil than at 3.75 (87%) and 15 (73%) mg Zn kg(-1) soil levels. Phosphorus additions up to 40 mgkg(-1) soil increased the plant-available Zn in soils whereas at higher P levels plant-available forms decreased with a concominant increase in the inert forms. At 160 mg P kg(-1) soil, the P effect was more pronounced in the shoot than in the root, suggesting that a higher P level inhibits Zn translocation from root to upper plant parts. Path analysis showed that the organically (PYR-Zn) and inorganically bound (AAC-Zn) Zn fractions were the predominant fractions that influenced the Zn availability to plants.

Crop residue addition effects on myriad forms and sorption of phosphorus in a Vertisol.

Crop residues are a vital organic resource and their extensive use in soil management for sustainable agriculture is widely advocated. The effects of soybean residue (SR) and wheat residue (WR) applied alone or in combination with fertilizer P (FP) on dynamics of labile P, distribution of P fractions and P sorption in a Vertisol (Typic Haplustert) were assessed in a 16 week long incubation study. The amount of P added through crop residues, FP or their combination was kept constant at 10 mg P kg(-1) soil. Addition of SR or WR resulted in net increase of labile inorganic (Pi) and organic (Po) P, and microbial P throughout the incubation period, except that the WR decreased labile Pi during the first two weeks due to Pi immobilization. Integration of FP with SR had no added benefit compared to SR alone, while use of FP + WR proved better in ensuring short-term P availability by offsetting initial P immobilization associated with WR alone. Sequential fractionation of soil P at the end of 16 weeks showed that addition of SR and WR alone or in combination with FP favoured a build-up in labile Pi and Po (NaHCO3-Pi and Po), and moderately labile Po (NaOH-Po) fractions at the expense of recalcitrant P (HCl-P). The P sorption capacity of soil and P required to maintain optimum solution P concentration of 0.2 mg P 1(-1) also decreased with addition of these crop residues. The implication of the results of this study is that soybean and wheat residues can potentially improve soil P fertility by increasing labile Pi and Po, and moderately labile Po fractions, decreasing P sorption and concomitantly causing dissolution of recalcitrant P in soil.

Relationship between C addition and storage in a Vertisol under soybean-wheat cropping system in sub-tropical central India

Kinetic relationship between addition of organic carbon (through unharvested crop biomass and externally applied farmyard manure) and storage in a Vertisol (Typic Haplustert) was studied in a seven-year soybean-wheat rotation experiment. We investigated 16 treatments comprised of combinations of four annual rates of farmyard manure (0, 4, 8 and 16 t ha—1 on dry weight basis) and four annual rates of fertilizer N (0, 72.5, 145, and 230 kg N ha—1). Average annual contribution of C input from soybean was 21.65% and from wheat was 32.32% of the harvestable above ground biomass. Net increases in the contents of soil organic C (Corg) at 0—15 and 15—30 cm depth were observed in all treatments. The annual rate of Corg enrichments ranged from 85 to 739 kg C ha—1 at 0—15 cm and 54 to 149 kg C ha—1 at 15—30 cm soil depth. The observed annual rate of change in Corg (δCs/δt, kg C ha—1 yr—1) at 0-30 cm was positively correlated with the gross annual C input (A, kg C ha—1 yr—1) to the 0—30 cm soil horizon, as described by a linear equation (δCs/δt = 0.1806 × A — 160.34; r = 0.978, P < 0.01). This indicates that 18.06% of the annual gross C input was incorporated in soil organic matter.

Growth and reproduction of the vermicomposting earthworm Perionyx excavatus as influenced by food materials

An outdoor study was undertaken using polyethylene containers to assess the suitability of different organic residues, soybean straw (Glycine max L. Merril.), wheat straw (Triticum aestivum L.), maize stover (Zea mays L.), chickpea straw (citer arietinum L.) and city garbage, as food for the tropical epigeic earthwormPerionyx excavatus, and to assess the influence of this earthworm on the decomposition of these materials. Maize stover was found to be the most suitable of the food materials used. Population growth ofP. excavatus was enhanced by addition of these organic materials in the temperature range 24°-30°C, while the population was adversely affected above 30°C in a vermiculture system. Addition of earthworms accelerated the breakdown of residues, which ultimately resulted in a lowering of the C:N ratio, water-soluble carbon and carbohydrates, and increased ash percentage and cation exchange capacity compared with their respective controls.

Sulfur mineralization in two soils amended with organic manures, crop residues, and green manures

The mineralization of sulfur (S) was investigated in a Vertisol and an Inceptisol amended with organic manures, green manures, and crop residues. Field-moist soils amended with 10 g kg -1 of organic materials were mixed with glass beads, placed in pyrex leaching tubes, leached with 0.01 M CaCl 2 to remove the mineral S and incubated at 30 °C. The leachates were collected every fortnight for 16 weeks and analyzed for SO 4 -S. The amount of S mineralized in control and in manure-amended soils was highest in the first week and decreased steadily thereafter. The total S mineralized in amended soils varied considerably depending on the type of organic materials incorporated and soil used. The cumulative amounts of S mineralized in amended soils ranged from 6.98 mg S (kg soil) -1 in Inceptisol amended with wheat straw to 34.38 mg S (kg soil) -1 in Vertisol amended with farmyard manure (FYM). Expressed as a percentage of the S added to soils, the S mineralized was higher in FYM treated soils (63.5 to 67.3 %) as compared to poultry manure amended soils (60.5 to 62.3 %). Similarly the percentage of S mineralization from subabul (Leucaena leucocephala) loppings was higher (53.6 to 55.5 %) than that from gliricidia (Gliricidia sepium) loppings (50.3 to 51.1 %). Regression analysis clearly indicated the dependence of S mineralization on the C : S ratio of the organic materials added to soil. The addition of organic amendments resulted in net immobilization of S when the C : S ratio was above 290:1 in Vertisol and 349:1 in Inceptisol. The mineralizable S pool (S o ) and first-order rate constant (k) varied considerably among the different types of organic materials added and soil. The S o values of FYM treated soils were higher than in subabul, gliricidia, and poultry manure treated soils.

Changes in organic and inorganic sulfur fractions and S mineralisation in a Typic Haplustert after long-term cropping with different fertiliser and organic manure inputs

Changes in the status of organic and inorganic pools of soil sulfur (S), total nitrogen (N), and organic carbon, and their interrelationships and S mineralisation were examined on a Typic Haplustert soil after a 27-year long-term cropping. The results indicated that NPK(+S) applied for 27 years at 50%, 100%, and 150% of optimum recommended rates and 100% NPK(+S) with farmyard manure (FYM) increased the organic C and total N status of soil compared with the control and the initial status of the soil. Intensive cropping with continuous use of 100% NPK without S resulted in depletion of total, organic, and inorganic S concentrations by 18.13%, 17.80%, and 21.72%, respectively, over the control, while the status of total, organic and inorganic S improved in plots that received graded rates of S with NPK and NPK plus FYM. Intensive cropping with continuous use of S-free NPK fertiliser (100% NPK-S) resulted in the widest C: N: S ratio in the soil. NaHCO 3 -extractable total, inorganic, and organic S fractions and NaOH-extractable total and inorganic S fractions were found to be better indices of soil S mineralisation than CaCl 2 -extractable inorganic S. Cumulative amounts of S mineralised during a 14-week incubation period varied between 2.3 and 21.3 mg S/kg soil and increased with an increase in the rates of S applied, along with NPK fertilisers. Incorporation of FYM with 100% NPK(+S) resulted in greater cumulative mineralised S over 100% NPK(+S) alone. The cumulative mineralised S showed a quadratic relationship with the duration of incubation in all the treatments.

Soil phosphorus dynamics in a Vertisol as affected by cattle manure and nitrogen fertilization in soybean‐wheat system

Repeated application of phosphorus (P) as superphosphate either alone or in conjunction with cattle manure and fertilizer N may affect the P balance and the forms and distribution of P in soil. During 7 years, we monitored 0.5 M NaHCO 3 extractable P (Olsen-P) and determined the changes in soil inorganic P (P i ) and organic P (P o ) caused by a yearly dose of 52 kg P ha -1 as superphosphate and different levels of cattle manure and fertilizer N application in a soybean-wheat system on Vertisol. In general, the contents of Olsen-P increased with conjunctive use of cattle manure. However, increasing rate of fertilizer nitrogen (N) reduced the Olsen-P due to larger P exploitation by crops. The average amount of fertilizer P required to increase Olsen-P by 1 mg kg -1 was 10.5 kg ha -1 without manure and application of 8 t manure reduced it to 8.3 kg ha -1 . Fertilizer P in excess of crop removal accumulated in labile (NaHCO 3 -P i and P o ) and moderately labile (NaOH-P i and P o ) fractions linearly and manure application enhanced accumulation of P o . The P recovered as sum of different fractions varied from 91.5 to 98.7% of total P (acid digested, P t ). Excess fertilizer P application in presence of manure led to increased levels of Olsen-P in both topsoil and subsoil. In accordance, the recovery of P t from the 0-15 cm layer was slightly less than the theoretical P (P added + change in soil P - P removed by crops) confirming that some of the topsoil P may have migrated to the subsoil. The P fractions were significantly correlated with apparent P balance and acted as sink for fertilizer P.

Long-term effects of intercropping and bio-litter recycling on soil biological activity and fertility status of sub-tropical soils

On-farm field experiments were carried out at two sites having 38- and 10-year-old orchard cropping systems under sub-tropical climatic regions to evaluate changes in organic carbon accumulation and chemical and microbiological properties of the soils. Under a system of different intercropped fruit trees, the cultivation of coconut (Cocos nucifera L.) intercropped with guava (Psidium guajava L.) enhanced the soil microbial activity approximately 2-fold after 38 yrs over 10 yrs of the same intercropped system. Soil organic carbon increased from 3.4 to 7.8 and 2.4 to 6.2 g kg-1 after 38 and 10 yrs, respectively, following the establishment of orchards. The increase was attributed to greater recycling of bio-litters. Levels of dehydrogenase, phosphatase and soil microbial biomass under field conditions generally depended more on the nature of the cropping system than on soil types. Similarly, average carbon inputs of bio-litter to the soil in monocrop (0.98 Mg ha-1 yr-1) was less than intercropped fruit trees (2.07 Mg ha-1 yr-1). The average level of soil microbial biomass carbon was 1158 kg ha-1 (0-0.15 m depth) and the organic carbon turnover rate was 8.5 yr-1 after 38 yrs of intercropped fruit trees, which resulted in a lower ratio (1.81) of carbon inputs to soil microbial biomass carbon.

Phytoaccumulation of lead by selected wetland plant species.

Several anthropogenic activities lead to the production of substantial amounts of aqueous effluents that contain various toxic trace and heavy metals and which pose potential threats to the wild habitat of wetlands. As a part of the remediation of heavy metals, it is necessary to identify some aquatic hyperaccumulator plants. To this end, a greenhouse study was conducted to investigate the phytotoxicity resulting from lead (Pb) and its accumulation in selected plant species. Lead was added from low to very high levels in a swell–shrink clayey soil (Typic Haplustert). Seven levels of Pb (0, 50, 100 200, 400, 600, and 800 mg kg–1 soil) were applied. Typha angustifolia L. of Typhaceae and Behaya plant (Ipomoea carnea L.) of the Convolvulaceae family were taken as test plants. Lead was added at high and low concentrations to determine whether an increase in concentration would Pb to an increased toxicity to the plants. Recorded weight of the Typha crop was reduced (6%) at 600 mg Pb kg–1 soil, and at greater doses of Pb, the dry-matter yield was inhibited considerably. In the case of Ipomoea, no growth retardation from Pb was observed. Most Pb accumulated in roots and then was transported to shoots. The Typha angustifolia L. and Ipomoea carnea L. plants show promise for the removal of Pb from contaminated wastewater because they can accumulate high concentrations of Pb in roots (1200 and 1500 mg Pb kg–1 respectively) and shoots (275 and 425 mg Pb kg–1 respectively). Lead uptake by both the plants increased with the increasing doses of Pb (50 to 800 mg kg–1 soil). Physiological parameters such as photosynthesis, respiration, chlorophyll content, and different enzyme activities including nitrate reductase (NR), peroxidase (POD), and succinate dehydrogenase (SD) were also studied for the evaluation of these plant species. In Typha plants, at greater doses of Pb, the rate of photosynthesis and chlorophyll content decreased whereas POD and SD activities increased to combat oxidative stress.