PCA and fuzzy clustering-based delineation of soil nutrient (S, B, Zn, Mn, Fe, and Cu) management zones of sub-tropical Northeastern India for precision nutrient management.

Understanding the spatial distribution of plant available soil nutrients and influencing soil properties and delineation soil nutrient management zones (MZs) are important for implementing precision nutrient management options (PNMO) in an area to achieve maintainable crop production. We assessed spatial distribution pattern of plant available sulphur (S) (PAS), boron (B) (PAB), zinc (PAZn), manganese (PAMn), iron (PAFe), and copper (PACu), and soil organic carbon (SOC), pH, and electrical conductivity (EC) to delineate soil nutrients MZs in northeastern region of India. A total of 17,471 representative surface (0-15 cm depth) soil samples were collected from the region, processed, and analysed for above-mentioned soil parameters. The values of PAS (0.22-99.2 mg kg-1), PAB (0.01-6.45 mg kg-1), PAZn (0.05-13.9 mg kg-1), PAMn (0.08-158 mg kg-1), PAFe (0.50-472 mg kg-1), PACu (0.01-19.2 mg kg-1), SOC (0.01-5.80%), pH (3.19-7.56) and EC (0.01-1.66 dS m-1) varied widely with coefficient of variation of 15.5-108%. The semivariogram analysis highlighted exponential, Gaussian and stable best fitted models for soil parameters with weak (PACu), moderate (PAB, PAZn, PAFe, SOC, pH, and EC) and strong (PAS, and PAMn) spatial dependence. The ordinary kriging interpolation revealed different distribution patterns of soil parameters. About 14.8, 27.5, and 3.40% area of the region had PAS of ≤15.0 mg kg-1, PAB of ≤0.50 mg kg-1, and PAZn of had ≤0.90 mg kg-1, respectively. About 67.5, and 32.5% area had SOC content >1.00 and < 1.00%, respectively. Soil pH was ≤5.50, and >5.50 to ≤6.50 in 41.7 and 40.3% area of the region, respectively. The techniques of principal component analysis and fuzzy c-mean algorithm clustering produced 6 MZs of the region with different areas and values of soil parameters. The MZs had different levels of deficiency pertaining to PAS, PAB, and PAZn. The produced MZ maps could be used for managing PAS, PAB, PAZn, SOC and soil pH in order to implement PNMO. The study highlighted the usefulness of MZ delineation technique for implementation of PNMO in different cultivated areas for sustainable crop production.

Synthesis and Performance Evaluation of Novel Bentonite-Supported Nanoscale Zero Valent Iron for Remediation of Arsenic Contaminated Water and Soil.

Groundwater arsenic (As) pollution is a naturally occurring phenomenon posing serious threats to human health. To mitigate this issue, we synthesized a novel bentonite-based engineered nano zero-valent iron (nZVI-Bento) material to remove As from contaminated soil and water. Sorption isotherm and kinetics models were employed to understand the mechanisms governing As removal. Experimental and model predicted values of adsorption capacity (qe or qt) were compared to evaluate the adequacy of the models, substantiated by error function analysis, and the best-fit model was selected based on corrected Akaike Information Criterion (AICc). The non-linear regression fitting of both adsorption isotherm and kinetic models revealed lower values of error and lower AICc values than the linear regression models. The pseudo-second-order (non-linear) fit was the best fit among kinetic models with the lowest AICc values, at 57.5 (nZVI-Bare) and 71.9 (nZVI-Bento), while the Freundlich equation was the best fit among the isotherm models, showing the lowest AICc values, at 105.5 (nZVI-Bare) and 105.1 (nZVI-Bento). The adsorption maxima (qmax) predicted by the non-linear Langmuir adsorption isotherm were 354.3 and 198.5 mg g-1 for nZVI-Bare and nZVI-Bento, respectively. The nZVI-Bento successfully reduced As in water (initial As concentration = 5 mg L-1; adsorbent dose = 0.5 g L-1) to below permissible limits for drinking water (10 µg L-1). The nZVI-Bento @ 1% (w/w) could stabilize As in soils by increasing the amorphous Fe bound fraction and significantly diminish the non-specific and specifically bound fraction of As in soil. Considering the enhanced stability of the novel nZVI-Bento (upto 60 days) as compared to the unmodified product, it is envisaged that the synthesized product could be effectively used for removing As from water to make it safe for human consumption.

Impact of wastewater irrigation on the dynamics of metal concentration in the vadose zone: simulation with NETPATH--part II.

Understanding and quantification of geochemical processes in vadose zone of sewage-effluent-irrigated soils are helpful in predicting the transference of metals and other ions to food chain and groundwater. Hence, an attempt has been made to simulate various geochemical processes occurring in the flow path of infiltrating sewage water down the vadose zone with the help of Net Geochemical Reaction Along the Flow Path (NETPATH). This study area was located in Western Delhi, India, where sewage effluents originating from Keshopur Sewage Treatment plant have been used for irrigation since 1979. Agricultural lands receiving irrigation through sewage and tube well water were selected for this study. The results indicated that groundwater of 20- and 10-year sewage-irrigated lands was slightly oversaturated in respect of calcite and dolomite, and undersaturated in respect of gypsum. The shallow groundwater of 5-year sewage-irrigated field was undersaturated in case of calcite, dolomite, and gypsum. Among the metals, major focus was given on Fe and Mn as these two metals are redox prone and relatively more mobile than other metals under saturated conditions. There was reduction in concentration of Fe and Mn in groundwater samples of 20-year sewage-irrigated field as compared to that in sewage effluent. Such reduction in concentration of Fe and Mn could be ascribed to the formation of goethite and manganite in vadose zone, respectively, as revealed by simulation with NETPATH. Similarly, in case of 10- and 5-year sewage-irrigated fields, increase in Fe and Mn concentrations in groundwater was due to dissolution of siderite and pyrulusite, respectively. NETPATH software could explain the variation in diethylene triamine pentaacetic acid (DTPA)-extractable Fe and Mn content in vadose zone to the extent of 94 and 65%, respectively.

Impact of wastewater irrigation on the dynamics of metal concentrations in the vadose zone: monitoring: part I.

Agricultural lands in the peri-urban area of New Delhi have been irrigated with treated wastewater from the Keshopur Effluent Irrigation Scheme (KEIS) since 1979. An attempt has been made to study the influence of wastewater irrigation on pH, electrical conductivity, organic carbon, and dynamics of heavy metal concentrations in vadose zone under KEIS. For this study, agricultural lands which have been receiving the sewage irrigation for 20, 10, and 5 years were selected. Adjacent tube well water-irrigated fields were selected and used as reference. Results indicate that there was a significant decrease in soil pH and electrical conductivity (EC) of sewage water-irrigated fields as compared to tube well water-irrigated fields. Organic carbon (OC) content in 20 years sewage-irrigated soil (0-15 cm) increased by 244% over tube well water-irrigated soil. The increases in organic carbon content for 10 and 5 years sewage-irrigated surface soil (0-15 cm) were 138 and 60% over tube well water-irrigated soils. The second-order polynomial model suggested that there is a possibility of accumulation of organic carbon in soil due to sewage irrigation at 1.55 t(-1) ha(-1) year. There was an increase in diethylene triamine pentaacetic acid (DTPA)-extractable Zn content in 20, 10, and 5 years sewage-irrigated soils (0-15 cm) to the extent of 86, 38, and 36% over tube well water-irrigated soils, respectively, while only 20 years sewage-irrigated soils showed a significant increase in DTPA-extractable Cu (289%) in surface layer (0-15 cm) over tube well-irrigated soils. In case of Fe, 127, 88, and 76.6% increases in available Fe content (DTPA-Fe) were recorded under 20, 10, and 5 years sewage-irrigated soils, respectively, over controls. Like Cu, DTPA-extractable Ni also exhibited a significant increase (42.2%) in 20 years sewage-irrigated soil over tube well-irrigated ones. It appears that due to sewage irrigation particularly in surface soil, DTPA-Mn content either remained same or showed a slight decline as compared to tube well-irrigated soils. The assessment of contamination factor (CF) in respect of total metal content in soil indicated the moderate level of metal contamination even after such long-term of sewage irrigation.

Co-Application of Silicate and Low-Arsenic-Accumulating Rice Cultivars Efficiently Reduces Human Exposure to Arsenic-A Case Study from West Bengal, India.

We investigated the effect of practically realizable doses of silicate on arsenic (As) uptake by differential-As-accumulating rice cultivars grown on geogenically As-polluted soil. The possible health risk from the dietary ingestion of As through rice was also assessed. In addition, a solution culture experiment was conducted to examine the role of root-secreted weak acids in differential As acquisition by rice cultivars. When grown without silicate, Badshabhog accumulated a much smaller amount of As in grain (0.11 mg kg-1) when compared to the other three varieties. Satabdi, IR-36, and Khitish accumulated As in grain beyond the permissible limit (0.2 mg kg-1) for human consumption. The application of silicate effectively reduced the As content in the grain, husk, and straw of all of the cultivars. The grain As content fell to 17.2 and 27.6% with the addition of sodium metasilicate at the rates of 250 and 500 mg kg-1, respectively. In the case of Khitish, the grain As content was brought down within permissible limits by the applied silicate (500 mg kg-1). The integrated use of low-As-accumulating cultivars and silicate has great potential to reduce the public health risks associated with As. A positive correlation between root-secreted total weak acid and grain As content could explain the different rice cultivars' differential As acquisition capacity.

Phytoextraction of nickel, lead, and chromium from contaminated soil using sunflower, marigold, and spinach: comparison of efficiency and fractionation study.

Heavy metals in soil pose a serious threat through their toxic effect on the human food chain. Phytoremediation is a clean and green potentially cost-effective technology in remediating the heavy metal-contaminated soil. However, the efficiency of phytoextraction is very often limited by low phytoavailability of heavy metals in soil, slow growth, and small biomass production of hyper-accumulator plants. To solve these issues, accumulator plant(s) with high biomass production and amendment(s) which can solubilize metals in soil is required for better phytoextraction. A pot experiment was conducted to assess the efficiency of phytoextraction of sunflower, marigold, and spinach as affected by the incorporation of Sesbania (solubilizer) and addition of gypsum (solubilizer) in nickel (Ni)-, lead (Pb)-, and chromium (Cr)-contaminated soil. A fractionation study was conducted to study the bioavailability of the heavy metals in contaminated soil after growing the accumulator plants and as affected by using soil amendments (Sesbania and gypsum). Results showed that marigold was the most efficient among the three accumulator plants in phytoextraction of the heavy metals in the contaminated soil. Both sunflower and marigold were able to reduce the bioavailability of the heavy metals in the post-harvest soil, which was reflected in their (heavy metals) lower concentration in subsequently grown paddy crop (straw). The fractionation study revealed that carbonate and organically bound fractions of the heavy metals control the bioavailability of the heavy metals in the experimental soil. Both Sesbania and gypsum were not effective in solubilizing the heavy metals in the experimental soil. Therefore, the possibility of using Sesbania and gypsum for solubilizing heavy metals in contaminated soil is ruled out.

Effect of sludge amelioration on yield, accumulation and translocation of heavy metals in soybean grown in acid and alkaline soils.

A greenhouse pot experiment was conducted with seven different levels of sludge (0, 5, 10, 20, 40, 80, 160 g kg-1) to assess the potential impact of sludge application on soybean (Glycine max (L.) Merr.) productivity, metal accumulation and translocation, and physico-chemical changes in acid and alkaline soils. The outcomes revealed that the application of sludge @ 5.0 to 160 g kg-1 resulted in a significant (p < 0.05) increase in seed and straw yield in both acid and alkaline soils compared to control. All the assessed heavy metals in soybean were within permissible ranges and did not exceed the phytotoxic limit, except for Fe, Zn, and Cu in the roots from the application of sewage sludge. The values of bioaccumulation factor (BFroot/soil) and translocation factor i.e., TFstraw/root and TFseed/straw were < 1.0 for Ni, Pb and Cr. Overall, for all the sludge application doses the soil pH was observed to increase in the acid soil and decline in alkaline soil when compared to the control. All the investigated heavy metals (Fe, Mn, Zn, Cu, Ni, Cd, Pb, and Cr) in the different plant tissues (root, straw and seed) of soybean were correlated with the soil variables. The study finds that sludge can be a potential organic fertilizer and function as an eco-friendly technique for the recycling of nutrients in the soil while keeping a check on the heavy metals' availability to plants.

Impact of long-term wastewater application on microbiological properties of vadose zone.

Impact of wastewater irrigation on some biological properties was studied in an area where treated sewage water is being supplied to the farmers since 1979 in the western part of National Capital Territory of New Delhi under Keshopur Effluent Irrigation Scheme. Three fields were selected which had been receiving irrigation through wastewater for last 20, 10 and 5 years. Two additional fields were selected in which the source of irrigation water was tubewell. The soil bacterial and fungal population density was studied in soil layers of 0-15, 15-30, 30-60 and 60-120 cm depths. Groundwater samples were collected from the piezometers installed in the field irrigated with sewage water for last 20, 10 and 5 years. Results indicate that there was significant increase in bacterial and fungal count in sewage-irrigated soils as compared to their respective control. The population density of bacteria and fungi in waste water-irrigated soils increased with the duration of sewage water application and decreased with increasing depth. The bacterial and fungal count was also directly proportional to organic carbon, sand and silt content and negatively correlated to the clay content, electrical conductivity, pH and bulk density of the soil. Groundwater under sewage-irrigated fields had higher values of most probable number (MPN) index as compared to that of tubewell water-irrigated fields. All the shallow and deep groundwaters were found to be contaminated with faecal coliforms. The vadose zone had filtered the faecal coliform to the tune of 98-99%, as the MPN index was reduced from ≥18,000 per 100 ml of applied waste water to 310 per 100 ml of groundwater under 20 years sewage-irrigated field. The corresponding values of MPN were 250 and 130 per 100 ml of shallow groundwater under 10 and 05 years sewage-irrigated fields, respectively. Rapid detection of faecal contamination suggested that the Citrobacter freundii and Salmonella were dominant in shallow groundwater, while Escherichia coli was dominant in deep groundwater collected from sewage-irrigated field.

Monitoring changes in soil organic carbon pools, nitrogen, phosphorus, and sulfur under different agricultural management practices in the tropics.

Soil organic matter not only affects sustainability of agricultural ecosystems, but also extremely important in maintaining overall quality of environment as soil contains a significant part of global carbon stock. Hence, we attempted to assess the influence of different tillage and nutrient management practices on various stabilized and active soil organic carbon pools, and their contribution to the extractable nitrogen phosphorus and sulfur. Our study confined to the assessment of impact of agricultural management practices on the soil organic carbon pools and extractable nutrients under three important cropping systems, viz. soybean-wheat, maize-wheat, and rice-wheat. Results indicated that there was marginal improvement in Walkley and Black content in soil under integrated and organic nutrient management treatments in soybean-wheat, maize-wheat, and rice-wheat after completion of four cropping cycles. Improvement in stabilized pools of soil organic carbon (SOC) was not proportional to the applied amount of organic manures. While, labile pools of SOC were increased with the increase in amount of added manures. Apparently, green manure (Sesbania) was more effective in enhancing the lability of SOC as compared to farmyard manure and crop residues. The KMnO(4)-oxidizable SOC proved to be more sensitive and consistent as an index of labile pool of SOC compared to microbial biomass carbon. Under different cropping sequences, labile fractions of soil organic carbon exerted consistent positive effect on the extractable nitrogen, phosphorus, and sulfur in soil.

Assessing equilibria of organo-arsenic complexes and predicting uptake of arsenic by wheat grain from organic matter amended soils.

In view of limited information, a laboratory experiment was conducted to study the stability of organo-arsenic complexes as affected by competing anions i.e. phosphate, nitrate and sulphate. For this purpose, humic acid (HA) and fulvic acid (FA) were extracted from farmyard manure (FYM), vermicompost (VC), sugarcane bagasse (SB) and soil. A pot experiment was also conducted with 4 levels each of arsenic (As) (10, 20, 30 and 40  mg  kg-1) and amendments (no amendment, FYM, VC and SB at the rate of 10  t  ha-1 each). Results indicate that stability of FA extracted from sugarcane bagasse have the highest stability constant (log K) as 9.77 and the corresponding mole ratio (x) value of 1.51. The phosphate was the most effective in replacing As from organo-As complexes followed by sulphate and nitrate. Under pot culture study, As content in wheat grain was the lowest in sugarcane bagasse amended soil followed by FYM and VC at all levels of As application. Solubility-free ion activity model was most effective in predicting As uptake by wheat grain based on Olsen extractable As, pH and Walkley & Black organic C. Efficacy of organic amendments in reducing health hazard for intake of As through consumption of wheat grain grown on contaminated soil was also reflected in the values of hazard quotient (HQ).

Enhancing the effectiveness of zinc, cadmium, and lead phytoextraction in polluted soils by using amendments and microorganisms.

For remediating polluted soils, phytoextraction of metals received considerable attention in recent years, although slow removal of metals remained a major constraint in this approach. We, therefore, studied the effect of selected organic and inorganic amendments on the solubility of zinc (Zn), cadmium (Cd), and lead (Pb) in polluted soil and enhancing the efficacy of phytoextraction of these metals by Indian mustard (Brassica juncea cv. Pusa Vijay). For this purpose, a greenhouse experiment was conducted using a metal-polluted soil to evaluate the effect of amendments, viz. green manure (T2), EDTA (T3), sulfur (S)+S oxidizing bacteria (Thiobacillus spp.) (T4), metal-solubilizing bacteria (Pseudomonas spp.) (T5), and green manure + metal-solubilizing bacteria (T6), on solubility and bioavailability of Zn, Cd, and Pb. Distribution of metals in different soil fractions revealed that Cd content in water soluble + exchangeable fraction increased to the extent of 34.1, 523, 133, 123, and 75.8% in T2, T3, T4, T5, and T6 treatments, respectively, over control (T1). Cadmium concentrations in soil solution as extracted by Rhizon sampler were recorded as 3.78, 88.1, 11.2, 6.29, and 4.27 µg L-1in T2, T3, T4, T5, and T6, respectively, whereas soil solution concentration of Cd in T1 was 0.99 µg L-1. Activities of Cd (pCd2+) in Baker soil extract were 12.2, 10.9, 6.72, 7.74, 7.67, and 7.05 for T1, T2, T3, T4, T5, and T6, respectively. Cadmium contents in shoot were recorded as 2.74, 3.12, 4.03, 4.55, 4.68, and 4.63 mg kg-1 in T1, T2, T3, T4, T5, and T6 treatments, respectively. Similar trend in Zn and Pb content with different magnitude was also observed across the different amendments. Cadmium uptake by shoot of mustard was enhanced to the extent of 125, 62.5, 175, 175, and 212% grown on T2-, T3-, T4-, T5-, and T6-treated soil, respectively, over T1. By and large, free ion activity of metals as measured by Baker soil test proved to be the most effective index for predicting Zn, Cd, and Pb content in shoot of mustard, followed by EDTA and DTPA. Among the metal fractions, only water soluble + exchangeable metal contributed positively towards plant uptake, which explained the variation in shoot Zn, Cd, and Pb content to the extent of 74, 81, and 87%, respectively, along with other soil metal fractions. Risk to human health for intake of metals through the consumption of leafy vegetable (mustard) grown on polluted soil in terms of hazard quotient (HQ) ranged from 0.64 to 1.10 for Cd and 0.11 to 0.34 for Pb, thus rendering mustard unfit for the human consumption. Novelty of the study mainly consisted of the use of natural means and microorganisms for enhancing solubility of metals in soil with the ultimate aim of hastening the phytoremediation.