Major nutrient management systems for rice-wheat cropping were compared for their potential to credit organic carbon (C) to the soil, its fractionation into active (very labile, VLc; labile, Lc) and passive (less labile, LLc; non-labile, NLc) pools, and crop yield responses. A ten-year long experiment was used to study effects of: (i) no inputs (Control, O), (ii) 100% inorganic fertilizers (F) compared to reduced fertilizers inputs (55%) supplemented with biomass incorporation from (iii) opportunity legume crop ( Vigna radiata ) (LE), (iv) green manure ( Sesbania aculeata ) (GM), (v) farmyard manure (FYM), (vi) wheat stubble (WS), and (vii) rice stubble (RS). Maximum C input to soil (as the percentage of C assimilated in the system) was in GM (36%) followed by RS (34%), WS (33%), LE (24%), and FYM (21%) compared to O (15%) and F (15%). Total C input to soil had a direct effect on soil C stock, soil C fractions (maximum in VLc and LLc), yet the responses in terms of biological yield were controlled by the quality of the biomass (C:N ratio, decomposition, etc. ) incorporated. Legume-based biomass inputs accrued most benefits for soil C sequestration and biological productivity.

Adequate nitrogen availability to plants for growth is one of the most important reasons for fertilizer application. Though organic alternatives are recommended, there is uncertainty of their nutrient release characteristics, especially during critical growth stages of a crop. In a 10-year-long experiment on nutrient management for rice-wheat cropping, ion exchange resin (IER) membrane strips were used as plant root simulators to determine daily NH 4 +-N and NO 3 −-N availability in soil solution during the rice growing season. The management included inorganic fertilizers at 100% recommended rate (F), compared to reduced rate (55%) of inorganic fertilizers supplemented with organic inputs via green manuring with Sesbania (GM), biomass incorporation of an opportunity legume crop-green gram (Vigna radiata) (LE), 1/3rd wheat stubble retention and soil incorporation (WS), 1/3rd rice stubble retention and soil incorporation (RS), and farmyard manure application (FYM). The total amount of available N (NH 4 + + NO 3 −) recorded for the full season was in the order GM (221 μg cm −2) > F (184 μg cm −2) > RS (181 μg cm −2) > FYM (176 μg cm −2) > WS (176 μg cm −2) > LE (175 μg cm −2). Both grain and straw yield related directly and significantly to the N mineralization in soil at 30-60 days after transplanting (DAT), indicating that fertilizer N application before 30 DAT and after 60 DAT could mostly be a loss in transplanted rice crop. Green manured (GM) soils maintained steadily high N mineralization rates throughout the rice growing period. The best alternative to cut down inorganic fertilizer use in rice cropping would be the biomass incorporation from leguminous green manuring crops. Integration of organics afforded almost 50% reduction in recommended inorganic fertilizer use while maintaining better N mineralization status at the critical growth stages of rice.

PurposeOne of the serious constraints for the integration of organics in soil fertility plans is the release and availability of nitrogen (N) to match the critical growth stages of a crop. The interplay between organic amendment characteristics and soil moisture conditions can significantly affect the nutrient release and availability, especially for dryland crops like wheat. In this study, the effects of integrated nutrient management strategies using diverse qualities of organic amendments on daily N mineralization and its availability to plants during the full growing season of the wheat crop were analyzed in a 10-year experiment.MethodsThe management included (1) F, inorganic fertilizers at 100% rate, compared to a reduced rate of inorganic fertilizers (55% N) supplemented with organic inputs via (2) GM, green manuring, (3) LE, legume cropping and its biomass recycling, (4) WS, wheat stubble retention, (5) RS, rice stubble retention, and (6) FYM, farmyard manure application, during the preceding rice season. Ion exchange resin (IER) membrane strips were used as plant root simulators to determine daily NH4+-N and NO3–-N availability in soil solution during the full wheat growing period.ResultsTotal available N for the full season was in the following order: GM (962 μg cm–2) > F (878 μg cm–2) > LE (872 μg cm–2) > FYM (865 μg cm–2) > RS (687 μg cm–2) > WS (649 μg cm–2). No significant differences were observed in NH4+-N availability throughout the cropping period as compared to NO3–-N which showed significant differences among management at critical crop growth stages.ConclusionLegume biomass incorporation (GM, LE) and farmyard manure (FYM) based management provided the most consistent supply equivalent to or even exceeding 100% inorganic fertilizers at several critical stages of growth, especially at tillering and stem elongation. Integration of organics in management increased nitrogen use efficiency 1.3–2.0 times, with cereal crop residue-based management having the highest efficiency followed by legume biomass incorporation.

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The competence of novel fungal consortium, consisting of Nigrospora sp. LDF00204 (accession no. KP732542) and Curvularia lunata LDF21 (accession no. KU664593), was investigated for the treatment of pulp and paper mill effluent. Fungal consortium exhibited enhanced biomass production under optimized medium conditions, i.e., glucose as carbon (C), sodium nitrate as nitrogen (N), C/N 1.5:0.5, pH 5, temperature 30 °C, and agitation 140 rpm, and significantly reduced biochemical oxygen demand (85.6%), chemical oxygen demand (80%), color (82.3%), and lignin concentration (76.1%) under catalytic enzyme activity; however, unutilized ligninolytic enzymes, such as laccase (Lac), manganese peroxidase (MnP), and lignin peroxidase (LiP), were observed to be 13.5, 11.4, and 9.4 U/ml after the third cycle of effluent treatment in repeated batch process. Scanning electron microscopy (SEM) of fungal consortium revealed their compatibility through intermingled hyphae and spores, while the FTIR spectra confirmed the alteration of functional groups ensuring structural changes during the effluent treatment. Gas chromatography/mass spectroscopy (GC-MS) analysis showed the reduction of complex compounds and development of numerous low-molecular-weight metabolites, such as 1-3-dimethyl benzene, 2-chloro-3-methyl butane, pentadecanoic acid, and 1-2-benzene dicarboxylic acid, during the treatment, demonstrating the massive potential of the novel fungal consortium to degrade recalcitrant industrial pollutants.