In this article we will discuss about the development and principles of System of Rice Intensification (SRI).
Development of SRI:
System of Rice Intensification (SRI) developed in Madagascar by Fe Henri de Laulanie in association with Non-Governmental Organisation-Association Tefy Sania (ATS) and many farmers in 1980s has spread to several countries including India. SRI, a “less water” method of production is ideal to poor fanners with relatively more family labour than land and capital.
The average yield obtained by SRI method, around 7 t ha-1 compared to world average around 3.8 t ha-1, require no new cultivars and only about half as much water per season as that of usual lowland rice. It has been tested in China, Indonesia, Cambodia, Thailand. Bangladesh and Sri Lanka with encouraging results.
Since SRI does not depend on purchased inputs, only changes in the way that plants, soil, water and nutrients (composted biomass) are managed. Reduced demand for water and the avoidance or reduction of fertiliser and other agrochemicals make SRI environmentally friendly.
Somewhat controversial are the very high yields obtained by farmers who use the method most skillfully and have improved their soil quality through SRI practices. Yields of 15 to 20 t ha-1 and even higher are beyond what has been considered the biological ceiling. However, this has been estimated for rice grown under continuous submergence and with large applications of fertilisers.
According to SRI concepts, those conventional practices reduce the achievable yield by contributing to degeneration of root system and by ignoring the fact that N uptake by rice roots is demand-led process.
The SRI practices produce a different phenotype from rice genomes, with more tillers (30 to 50 commonly; around 80 to 100 for individual plants); deeper and more effective roots (root resistance around 5 times greater for conventionally grown plants); and a positive correlation between tillering and grain filling (literature indicate inverse relation, probably due to continuous submergence and high rates of N application).
These phenotypic responses to SRI management have been reported with all rice varieties, traditional as well as high yielding. Because SRI was developed empirically and has been ‘practice-led’, the scientific basis for its performance is not fully understood. Evidence on phenotypic differences attributable to SRI practices have been reported.
Some studies also indicate contribution of biological nitrogen fixation and phosphorus solubilisation to high yield of SRI. All these contributions may be more conjunctive than established facts. There are more unanswered questions raised by SRI than there are answers on hand. Management practices for SRI are summarised.
Principles of SRI:
SRI has seven basic principles:
i. Land preparation:
Required moisture level has to be maintained uniformly. For best results, SRI requires careful ploughing, puddling, leveling and raking, with drainage facilitated by 30 cm wide channels at 2 m intervals across the field.
ii. Nurseries:
Seedbeds have to be nutrient-rich and established as close to the main field as possible. This will enable quicker and easier transportation between the nurseries and the fields, minimising both transport time and costs so that the seedlings are efficiently transplanted. No chemicals are applied to the seedbeds.
iii. Transplanting:
This has to take place when the seedlings are just 8 to 12 days old, soon after they have two leaves and at least before the 15th day after sowing. Seedlings must be transplanted with their roots intact, while the seed sac is still attached. They must not be plunged too deep into the soil, but placed on the ground at the appropriate point on the planting grid.
Transplanting should be at 1 -2 cm depth at the most. Transplanting should be done quickly, after gently removing seedlings from the nursery bed. The roots should not dry out. Care should be taken to avoid causing trauma to the roots.
iv. Spacing:
Seedlings should be planted at precise spacing, usually 25 x 25 cm, about 16 plants per square meter. Rice plant roots and canopies grow better if spaced widely, rather than densely. This exposes each plant to more sunlight, air and soil nutrients and allows easier access for weeding.
v. Soil nutrients:
It is better to use organic nutrients, as they are better at promoting the abundance and diversity of microorganisms, starting with beneficial bacteria and fungi in the soil. This will promote proper microbial activity, thereby improving production. Under SRI method, even farmers who do not have access to organic manure may use less chemical fertilisers.
vi. Watering:
SRI requires the root zone to be kept moist, not submerged. Such management encourages more extensive, healthy root systems and avoids root degeneration. More intensive management involves daily application of small amounts of water on a leveled field. Reliable and precise irrigation service delivery is important — especially in the early growth period.
Once the roots are well established, irrigation can be halted for three to six days at a time to encourage downward root growth. Some drying out of the soil is beneficial for the roots and soil organisms. SRI uses much less water than conventional methods of rice cultivation.
vii. Weeding:
Since there is no standing water and no continuous submergence of rice plants under SRI, weeds tend to proliferate, requiring careful and frequent weeding. The first weeding has to be done within 10 to 12 days of transplantation and further weeding may be required at intervals of 10-12 days. Weeding must continue until the crop has grown to such level that the canopy obviates weeding.
viii. Cost-effective in every way:
The System of Rice Intensification improves yields with less water, less seed and less chemical inputs than most conventional methods of rice cultivation. This means that the returns on inputs are higher, making the method potentially more profitable than most of the traditional methods.
Initially, it does require significantly more labour – mainly for preparing land and weeding. SRI could contribute to job creation in rural areas. It is a different matter that SRI is becoming popular more for the obvious overall productivity gains in land, labour, water and capital.
ix. Higher yields:
SRI improves the productivity of land, labour, water and capital used in rice cultivation. Implementation of SRI has helped improve the yield of local varieties by between 6 and 8 t ha-1. With improved management, hybrid varieties have yielded between 10 and 12 t ha-1 under SRI.
Often a 20 to 40 per cent increase in yield compared to that under conventional methods is observed in SRI. However, the actual yield increases depend on how well farmers practice SRI. It improves the productivity of land, labour, water and capital used in rice cultivation.