Fitting green manures in rice based cropping systems – A review

In lowland rice ecosystems, green manure is considered to be the appropriate organic source. But this necessitates farmers to set apart 6 to 8 weeks exclusively for growing green manure crops. Due to its unattractive economics, crop intensification, ease in application and ready availability of inorganic N fertilizer, the use of green manures has declined. So if green manure is to be popularized, the capital, time and labour involved in raising a green manure crop and the economical competition with other high value cash crops should be minimized which can render it as a potential component of Low Input Sustainable Agriculture. A method of introducing the green manures in the rice based cropping system without unduly affecting the net returns to the farmers is imperative. Intercropping of Sesbania with cowpea in post-rice season recorded a net return of US $ 593 ha⁻¹ from a combination of cowpea and sesbania rows in the ratio of 3: 1. Sesbania rostrata is proved to be a more efficient green manure crop for intercropping in the semi-dry rice which produced 9078 kg ha⁻¹ biomass and 1389 kg ha⁻¹ of dry matter. The research findings on the opportunities for fitting green manures in the rice based cropping systems and alternate uses of green manures are reviewed.