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Soil organic C (SOC) pools under long‐term management practices provide information on C sequestration pathways, soil quality maintenance, and crop productivity. Farmyard manure (FYM), paddy straw (PS), and green manure (GM) along with inorganic fertilizers were used in a 19‐yr‐old rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping system in subtropical India to evaluate their impact on SOC stock, its different pools—total organic C (Ctot); oxidizable organic C (Coc) and its four fractions of very labile (Cfrac1), labile (Cfrac2), less labile (Cfrac3), and nonlabile C (Cfrac4); microbial biomass C (Cmic); and mineralizable C (Cmin). Cropping with only N–P–K fertilization just maintained SOC content, while N–P–K plus organics increased SOC by 24.3% over the control, their relative efficacy being FYM > PS > GM. A minimum of 3.56 Mg C ha−1 yr−1 was required to be added as organic amendments to compensate for SOC loss from cropping. The passive (Cfrac3 + Cfrac4) pool and Cmin constituted about 39 and 11.5%, respectively, of Ctot Organics contributed toward the passive pool in the order FYM > PS > GM. Most of the pools were significantly (P = 0.005) correlated with each other. Yield and sustainable yield index were strongly related with Cfrac1, Coc, Cmic, and Cmin Results suggest Cfrac1 as a useful indicator for assessing soil health, and balanced fertilization with FYM as suitable management for sustaining crop productivity of the rice–wheat system.

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Abstract:Linseed is an industrial crop cultivated for its seeds, fibres and oil purpose. Linseed crop can met their requirement i.e. moisture and nutritional demand from stored soil moisture and residual fertility status in "utera" or "paira" system of cropping. On the basis of this fact an experiment was conducted on "Seed yield of linseed varieties grown as paira crop as influenced by dates of sowing" in red and laterite zone of West Bengal during rabi season of 2012-13 and 2013-14 at Rice Research Station, Bankura, West Bengal, India. Poor in organic matter content, available phosphate and bases, hard structure of iron and aluminium patterned as honeycomb are present in the subsurface regions of the profiles and kaolinite is the predominant clay minerals of red and lateritic zone (western part) of West Bengal. This experiment was laid out in a split-plot design with three replications and compared two factors (dates of sowing and linseed varieties). Objective was identifying the optimum date of sowing and suitable linseed varieties grown as "paira" crop under changed climate in red and laterite zone of West Bengal. as pooled value). Lowest seed yield (409. 3 kg ha -1 as pooled data) was recorded from Neela variety. From the present study it may be concluded that linseed sown on 15 th November is the best time and T-397 is the suitable linseed variety grown as "paira" crop under changed climate in red and laterite zone of West Bengal.