What Is SRI? Systematic Rice Intensification

To summarize the methodology most succinctly, SRI achieves these improvements in yield and factor productivity by changing some of the plant, soil, water and nutrient management practices long associated with irrigated rice production.

SRI practices promote greater root growth that is easily verifiable and more soil biological activity, which is not so visible. SRI does not depend on purchased, external inputs. Instead, it increases the productivity of the land, labor, water and capital devoted to irrigated rice production by capitalizing on existing genetic potentials and by biological processes, particularly in the soil.

The basic concepts constituting SRI are three. They are to be applied with adjustments in specific practices like spacing and timing as appropriate to local conditions.

Transplant seedlings while still young, <15 days, i.e., prior to the start of the 4th phyllochron of growth. This preserves plants' potential for tillering and root growth that is reduced by later transplanting later. Direct seeding is an option, however, since what is important is that plant roots not be traumatized after they start their growth trajectory, on or about the 15th day. Careful transplanting promotes rapid resumption of growth.

Maintain wide spacing between plants -- with preferably just one plant per hill, and set themout in a square pattern, 25x25, cm or even wider if soil fertility is good. This gives room for profuse root and tiller growth, achieving 'the border effect' throughout the whole field.

Keep the soil both moist and aerated, at least during the vegetative growth period, so that roots have access to both oxygen and water. Under continuously hypoxic conditions, rice roots degenerate, with as many as 75% dysfunctional by panicle initiation

Specific practices include in addition to using young seedlings with still only two leaves, planted singly and widely spaced: frequent weeding, preferably with a rotating hoe that aerates the soil while it prevents weeds' growth by churning them into the soil; application of small amounts of water daily, or alternate flooding and drying of fields for 3 to 6-day periods; and providing organic matter to the soil. This can be any decomposed biomass, including rice straw or weeds; manure or mulch can also be used. Green manures and cover crops are being experimented with, and we think that SRI may converge with conservation agriculture practices in the next few years.

Results Associated with SRI

Increased tillering, with 30-50 tillers per plant, 80 to 100 possible, and sometimes even more from a single plant. This is the most obvious and dramatic result.

Greater root growth, with 5-6 times more force required to uproot an SRI plant than to pull up one conventionally grown; see picture on next page which shows root growth potential.

Increased grain filling.
Panicles are larger as well as more numerous. This goes against the view in the literature that there is a negative correlation between panicle number and panicle size.

Higher grain quality and greater grain weight.
Millers in India and Sri Lanka are willing to pay more for SRI paddy rice because it has fewer unfilled grains and fewer broken grains after milling. There have also been reports of reduced chalkiness. With SRI we often get heavier, denser grains that withstand shattering and keep their shape better after cooking. Fortunately, the grains do not become larger (coarser) so that they lose market value.

Water savings.
Water requirements with SRI are usually reduced by about half since paddies are not kept flooded during the entire crop cycle. Water is much reduced during the vegetative growth phase, and only a minimum of water is kept on the field during the reproductive phase. This will become increasingly important in the agricultural sector.

Other Benefits with SRI

Less lodging.
Because of stronger tillers and larger root systems, SRI plots withstood the wind and rain of a recent cyclone that hit Andhra Pradesh while neighboring fields were blown down and their grain submerged.

Fewer pest and disease attacks.
This is widely reported by SRI farmers; 88% of the 60 SRI farmers interviewed for an evaluation in Sri Lanka, chosen at random in two districts, said that they had fewer pest and disease attacks (91% said less lodging). Farmers thus can avoid or reduce their expenditures on agrochemical applications.

Seed savings.
Because many fewer plants are grown, the seeding rate is only 5-10 kg/ha. This is a benefit particularly for hybrid rice where seed cost can be a barrier for adoption.

No need to purchase new seeds.
Farmers can use whatever varieties they are already planting since SRI methods enhance yield for traditional as well as improved cultivars.

No need for chemical fertilizers.
While these increase yield with SRI methods, compost or any decomposed biomass usually gives even better results. Compost requires more labor but saves cash and avoids the need to borrow money, something important for poorer farmers.

Lower costs of production. With external input requirements reduced, farmers can save substantial expenditure at the same time that yields are increased. Costs of production per kg are reduced from 25 to 100% depending on practices and resulting yields.

Increased factor productivity.
The returns to farmers' land (yield per hectare), labor (income per hour), water (output per m) and capital (profitability) all increase at the same time as SRI practices enable plants to get the benefits of greater supplies of carbon, nitrogen and oxygen.

Profitability.
The most detailed analysis of this is the evaluation done Sri Lanka. Farmers in the sample were not using the full set of SRI practices and had lower increases in SRI yield (50%) than many other farmers in that country. Even so, given their lower production costs, net revenue with SRI practices went up between 83 and 206%, depending on the wage rate
assumed. In an evaluation of SRI in Sri Lanka, SRI costs of production (rupees/kg) were calculated to be 111 or 209% lower, in yala (dry) and maha (wet) seasons respectively, assuming unpaid family labor, compared to conventionalproduction methods, and 17 or 27% lower when figuring labor costs at the standard farm wage.

Reduced risk.
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. The evaluation of SRI use in Sri Lanka found that, considering different rates of labor remuneration, that conventional farmers had net losses from their rice production in 28% of their seasons; SRI farmers in only 4%.

Any of these benefits would be worth pursuing. That all can come together in one set of changes in production methods is hard to believe. Many persons have rejected SRI simply on logical or a priori grounds, without giving the methods a trial. Fortunately, a growing network of NGOs, researchers, administrators and individuals (e.g., retirees) working together with farmers in Asia, Africa and Latin America have been willing to test SRI and demonstrate its opportunities. Farmers themselves have begun making improvements in SRI methods and implements, and many have voluntarily undertaken to spread knowledge of the techniques to their peers because of their enthusiasm about its profitability and environmental benefits.


Regds

Manoj Singh