The System of Rice Intensification (SRI) is a yield-increasing methodology practiced by probably more than 20 million farmers, with benefits having been demonstrated in over 60 countries. SRI methods modify the most common rice-growing practices in a number of ways. The changes include: (1) growing seedlings in nurseries with a minimum of water, a maximum of organic matter, and low plant density; (2) transplanting seedlings into rice fields at a young age, as little as 10-12 days old and no more than 15 days; (3) planting single (rather than multiple) seedlings in hills in a square pattern at a distance of 25-30 cm; this encourages healthy root growth with reduced competition for nutrients and induces profuse tillering and canopy growth; (4) mechanical weeding that eliminates weeds at the same time it aerates the top layer of soil; (5) using organic matter, as much as available, to enhance soil fertility in preference to chemical fertilizers; and (6) intermittent irrigation, alternating wetting and drying of rice paddies instead of continuous flooding as this favors aerobic over anaerobic microorganisms. Fertilizers can be used where there is not sufficient organic matter to meet soil and plant needs, but results are better to the extent that the soil’s reserves of organic matter are enhanced. Also, organic and inorganic nutrient sources can be combined (optimized) when the first are limited or the soil has particular deficiencies, but the purpose is to be supporting soil microbial communities, not just the plants.
SRI methods not only increase the production of rice, but also the biodiversity in the soil, giving plants greater resistance against pest infestation and to some extent reducing the uptake of arsenic. SRI also helps to conserve rice biodiversity by giving farmers financial incentive to plant local/indigenous/heirloom varieties. Thousands of these varieties have already become extinct, and most of the surviving varieties face extinction. SRI methods can make producing traditional varieties more profitable by raising their yields while reducing costs of production; these varieties usually command a higher market price because of consumers’ tastes and preferences. So even if their yields are not as high as from ‘improved’ varieties, they can be more remunerative. Furthermore, when SRI methods are used, soil and water quality are improved.
Growing rice plants with SRI methods enhances their root growth while the roots support the plants’ canopy, leaf and tiller growth, and grain filling. These plants have better physiological performance such as higher rates of photosynthesis that increase the supply of carbohydrates to the roots which prolongs the roots’ longevity and thereby contributes to the grain-filling process. Under SRI management, yields are increased by 20–60% or even more, while water requirements are reduced by about 25%. According to some research in India, net greenhouse gas emissions, consumptions of ground-water, and fossil energy use are, respectively, lower by 40%, 60%, and 74% kg−1 paddy rice produced compared to standard practices. Farmers’ net returns ha−1 were increased by as much as 300%.