System of rice (Oryza sativa) intensification for higher productivity and resource use efficiency–A review
System of rice intensification (SRI) is a new method of rice (Oryza sativa L.) culture. This is an environment and ecology benign method that increases productivity and resource-use efficiency of irrigated rice by changing the way of managing soil, plants, water and nutrients. Emerged by chance in 1980s in Madagascar, it is now practiced on research farms and farmers’ fields in about 60 countries world-over. A record yield of 19 tonnes/ha has been reported by China, while in India 50–100% increases in yield have been reported over conventional rice culture. As per the general notion, SRI is not cultivar-specific. However, differential yield responses of cultivars have been observed under SRI at different locations in the country. SRI has been found to enhance yield of hybrids, and long- and medium-duration cultivars more than those of short-duration improved cultivars, and hence these are found more suitable for cultivation under SRI. Yield enhancement with SRI was greater under constrained soil conditions like acidic soils, red lateritic soil, etc. Wider spacing is one of the important principles of SRI and influences growth and yield of rice. Initially, planting spacing ranging from 25 cm × 25 cm to 50 cm × 50 cm was prescribed, but lateron wide spread experiments across the world showed 25 cm × 25 cm to be the best planting spacing for SRI. However, some studies have suggested even lower spacing 20 cm × 20 cm to be ideal for SRI. Spacing of 25 cm × 25 cm seems to be better in kharif season, while in rabi season in southern India, 20 cm × 20 cm spacing appears to more rewarding than 25 cm × 25 cm. Seedling age of 10–12 days is invariably found suitable for transplanting to obtain higher yield and resource-use efficiency. Although under SRI yields were best when irrigations were scheduled at 3 days after disappearance of ponded water (DADPW), but larger water savings with some yield penalty suggests the delaying irrigations till 5 or 7 DADPW. Regarding nutrient management, it could be concluded that yield, profitability and resource-use efficiency from SRI under integrated nutrient management capsule consisting of 50% RDF + 50% nutrients from organic sources were either higher or equal to those obtained from the use of 100% RDF. Weeds infestation is more in SRI, which could be managed most economically by employing integrated weed management, using cono-weeder as one of the component.
Cultivar, Irrigation, Nutrient management, Rice yield, Seedling age, Spacing, System of rice intensification, Weed.