The system of rice intensification (SRI) was developed in Madagascar in 1980s. It has yet to make debut in Pakistan. The SRI is a method of production using less water with relatively more family labour than land and capital.
The average yield obtained is higher which requires no new cultivars. Since the SRI does not depend on purchased inputs, only changes in the way to plant, soil, water and nutrients (composted biomass) are managed. Reduced demand for water and the avoidance or reduction of fertilizer and other agro-chemicals make SRI environmental friendly.
The SRI practices produce a different phenotype from rice genome, with more tillers, deeper and more effective roots and a positive correlation between tillering and grain filling.
These phenotypic responses to the SRI management have been reported with all rice varieties, traditional as well as high yielding.
As the SRI has been developed empirically, the scientific basis for its performance is not fully understood. Evidence on phenotypic differences attributable to the SRI practices is reported.
Some studies indicate contribution of biological nitrogen fixation and phosphorus solublisation to high yield of the SRI. All these contributions may be more conjunctive than the established facts.
Benefits: Eight to twelve days old seedlings with just two leaves are transplanted ensuring more tillers and root growth. Panicles are larger and more numerous. Water requirements are reduced by about half since paddies are not kept flooded during the entire crop cycle.
Water is reduced during the vegetative growth phase, and only minimum water is left in the field during reproductive phase. Compost or any decomposed biomass usually gives better results.
Compost requires more labour but saves cash and the need to borrow money, something important for poorer farmers.
Cost of production per kg is reduced from 25 to 100 per cent depending on the practices and resulting yields.
In addition to better withstanding storm damage and pest and disease attacks, the larger root systems increase resistance to drought, the other main hazard for rice farmers.
Biological support for rice production: The SRI appears “too good to be true”. Fewer external inputs can produce more output by using less water (avoiding soil hypoxia) and chemical fertilizer (affecting micro organisms) by enhancing biological activity. Fewer chemical sprays leave more beneficial organisms in the canopy and soil to control pests.
With reduced external inputs, there is more input to crop production processes as well as biological mineralization of nutrients in the soil. The beneficial and necessary contribution of root supports larger and more diverse microbial populations.
There are a number of biological processes that could boost rice yields with the SRI management of plants, soil, water and nutrients. When soils are alternately flooded and drained, this gives both aerobic and anaerobic bacteria as well as mycorrhizal fungi an opportunity to contribute to plant growth.
Under these conditions, there is an increased biological N fixation. Plants with larger root systems and canopies are able, indirectly, to produce more N in their root zone by exuding photosynthates made from the atmospheric CO2 into the rhizosphere.
These photosynthates support larger bacterial populations on the roots that in turn are “grazed” by protozoa which then excrete excess N onto the plant roots which utilize this biological waste product. Management practices for SRI are nursery management, manure, water and weed.
Constraints and costs: There are some limitations on the use and adoption of the SRI. The most important is to have good water control for best results.
By saving water and keeping soil aerated enough to support the growth and functioning of aerobes farmers are advised to apply limited amount of water rather than keeping their paddies continuously flooded.
Many farmers do not have such water control as they operate in field-to-field systems of distribution. Once the benefits are known, even sacrificing a little field area will become attractive.
Initially, the SRI requires more labour with the first-season increase usually by 25-50 per cent along with higher returns. Another requirement is motivation and skill since time and effort are needed to disseminate the technique correctly to farmers.
Farmers who know how to grow irrigated rice and are motivated to learn the SRI can do this with little instruction.