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Decline in soil organic carbon (SOC) content is considered a key constraint for sustenance of rice-wheat system (RWS) productivity in the Indo-Gangetic Plain region. We, therefore, studied the effects of fertilisers and manures on SOC pools, and their relationships with crop yields after 18 years of continuous RWS. Total organic C increased significantly with the integrated use of fertilisers and organic sources (from 13 to 16.03 g [kg.sup.-1]) compared with unfertilised control (11.5 g [kg.sup.-1]) or sole fertiliser (NPKZn; 12.17 g [kg.sup.-1]) treatment at 0-7.5 cm soil depth. Averaged across soil depths, labile fractions like microbial biomass C (MBC) and permanganate-oxidisable C (PmOC) were generally higher in treatments that received farmyard manure (PYM), sulfitation pressmud (SPM) or green gram residue (GR) along with NPK fertiliser, ranging from 192 to 276 mg [kg.sup.-1] and from 0.60 to 0.75 g [kg.sup.-1] respectively compared with NPKZn and NPK+cereal residue (CR) treatments, in which MBC and PmOC ranged from 118 to 170 mg [kg.sup.-1] and from 0.43 to 0.57 g [kg.sup.-1] respectively. Oxidisable organic C fractions revealed that very labile C and labile C fractions were much larger in the NPK + F YM or NPK+GR + F YM treatments, whereas the less-labile C and non-labile C fractions were larger under control and NPK + CR treatments. On average, Walkley-Black C, PmOC and MBC contributed 29-46%, 4.7-6.6% and 1.16-2.40% towards TOC respectively. Integrated plant nutrient supply options, except NPK + CR, also produced sustainable high yields of RWS. Additional keywords: cereal residue, FYM, green gram residue, Inceptisol, labile SOC, sulphitation pressmud., Introduction In the post-Green Revolution era, Indian agriculture encountered the problems of deterioration in soil health, stagnation in both food grain production and productivity growth rates and groundwater recession, resulting [...]

An attempt has been made to assess the geoavailability of heavy metals in polluted soils using short sequential fractionation schemes. For this purpose, 25 composite soil samples were collected from various locations (across India) of which had a history of receiving sewage sludge, municipal solid waste, polluted river water and industrial effluents. Four composite soil samples were also collected from adjacent fields which had not received contaminated amendments. Zinc (Zn), copper (Cu), nickel (Ni), lead (Pb) and cadmium (Cd) were extracted from the soil solution plus exchangeable, carbonate bound, Fe and Mn oxides bound, and organic matter bound fractions. Copper (53.0%) was largely adsorbed by the organic fractions, while a significant amount of Zn (56.6%), Ni (78.4%), Pb (57.4%), and Cd (59.7%) was extracted from the Fe/Mn oxide bound fraction. Regression analysis revealed that water-soluble plus exchangeable pool of Zn, Cu, Ni, Pb and Cd contributed positively towards the uptake of these elements by spinach and wheat under pot experiment. Behaviour, transport and the ultimate fate of heavy metals in the soil environment depend largely on their association with different geochemical fractions of the soil which is related to the mineralogical origin of the metals. [ABSTRACT FROM AUTHOR]

This study assessed the effect of land use systems (rice-fallow, bamboo, mandarin and forest) along an altitude gradient (<500, 500–1000 and > 1000 m asl) and soil depth (0–15, 15–30 and 30–45 cm) on C stability in naturally occurring clay-organic complex (NOCOC) and their relationship with soil properties. The C stability in NOCOC (1/k) was determined from desorption rate constant (k) of humus-C by sequential extraction and was correlated with soil properties across the altitude. The C stability in NOCOC decreased (34%) with increasing soil depth from 0–15 to 30–45 cm. Across the altitudes, highest C stability in NOCOC was at > 1000 m asl (8.37 h) which was 12.7 and 9.4% higher than 500–1000 and < 500 m asl, respectively. Irrespective of soil depth and altitude, forest (5.30 h) showed the greatest C stability in NOCOC followed by mandarin (4.64 h), bamboo (4.20 h) and rice-fallow (3.85 h). Measurable soil properties could explain 90–94% variability of C stability in NOCOC across the altitude. Furthermore, C stability in NOCOC increased macroaggregate formation (0.25 mm) and ensured greater physical, chemical and microbial protection of organic C in soil. [ABSTRACT FROM AUTHOR]