Productivity, soil fertility and sustainability of continuous rice system under long term substitution of nitrogen through organics

A permanent plot experiment was being conducted since 1988 on Inceptisols of College of Agriculture, Rajendranagar to study the long term effects of chemical fertilizers alone and in combination with organic sources on the sustainability and soil fertility under rice-rice cropping system. The study was made with 12 treatments in which major nutrients were supplied either through fertilizers alone or in conjunction with FYM, paddy straw or gliricidia at 50% and 25% substitution level of nitrogen during kharif and with fertilizers alone to supply 75 and 100% recommended dose of fertilizer during rabi. The system productivity of rice averaged over 24 years was highest in plots which received 50% N through gliricidia+50% RDF in kharif and 100% RDF in rabi seasons. However, the sustainability yield index of rice-rice system was highest (0.67) when all the nutrients were applied through fertilizers during both the seasons, and also when 25% N was substituted through gliricidia during kharif and 25% NPK was saved during rabi season. However, improvement in soil organic carbon content was more prominent when 25% or 50% of N was substituted through paddy straw and FYM during kharif season With all the nutrient management practices, available nitrogen in the soil was maintained, there was a build-up of available phosphorus, while available potassium was depleted considerably.