Abstract

The potential benefits of rice straw in organic farming in terms of rice productivity, soil organic carbon (SOC) stocks, carbon sequestration rate (CSR) and global warming potential (GWP) were studied for five years covering 10 wet (kharif) and dry (rabi) seasons with a wide seasonal temperature range (28-31 C and 30-40 C during wet and dry seasons, respectively). Field experiments were conducted at the ICAR-IIRR, Hyderabad, in a black clayey vertisol. The organic sources used were rice straw + green manure in kharif and rice straw + poultry manure in rabi. Organic system resulted in initial yield reduction by 15-20% than inorganic system and yields stabilized after two and five years in wet and dry seasons, respectively, with improved soil health parameters. The SOC stocks were higher with organics by 34-43% compared to inorganics after five years of study. The CSR was also positive with organics (0.97 and 0.57 t/ha/ year during wet and dry seasons, respectively) compared to inorganics (-021 and -0.33 t/ha/year during wet and dry seasons, respectively) which recorded negative C sequestration rate. Organics recorded favourable C sequestration even under dry situations which is more desirable to mitigate the adverse effects of global warming to certain extent by reducing CO2 emissions. The global warming potential under organic system was 20% higher than in conventional system with increased CO2 and CH4 and reduced N2O emissions. Since GWP was higher with rice straw, mixing of straw with other potential organics in proper proportions reduce the GWP in addition to carbon sequestration in organic rice cultivation.