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Several different studies in Madagascar, where average rice yields are currently 2 t/ha, have shown that with SRI methods an average yield around 8 tons per hectare (t/ha) is attainable. High yields are in the 12-15 t/ha range, while some low yields of 3-4 t/ha.

Maximum yields, obtained with the most skillful use of SRI techniques and after soil quality has been improved by good management methods, are in the range of 15-20 t/ha, and a few farmers have topped 20 t/ha.

However, we prefer to stress gains in productivity rather than yields as such, since increased productivity of land, labor and water are most beneficial to farm households and to a country.

Since Madagascar soils are among the poorest in the world, these yield gains are not due to inherent soil fertility. Rather, the increases are the result of management practices that increase root growth and concomitant tillering, both visible and measurable effects. As SRI methods are being tried and evaluated in other countries, similar yields are being reported elsewhere.

When rice is grown under continuously flooded, hypoxic conditions, there is stunted root growth and root degeneration. As much as 3/4 of the roots may degenerate by the time of panicle initiation and the start of the plant's grain production (Kar et al., 1974). This process of root die-back contributes to the negative correlation between the number of tillers per plant and the number of grains per fertile tiller (panicle) that has been observed with irrigated rice when grown with standard practices.

With SRI methods -- which keep the root zone aerated -- there is a positive correlation between tillering and grain filling. This reversed relationship is what makes possible the very large increases in yield, coupled with improvements in soil quality and dynamics.

With SRI, massive root growth makes the rice plant more of an "open system" -- rather than the "closed system" that it is under conventional growth conditions, when root growth is limited and about 75% of roots are in the top 6 cm of soil.

The rice plant genome has productive potential that has not been tapped because conventional management practices -- flooded soil, close planting, mature seedlings -- have constrained root growth and tillering, with resulting reduction in grain filling. Soil conditions have likewise been suboptimal for nutrient provision and recycling.

The concept of a "yield ceiling" for rice between 12 and 15 t/ha, proposed by some rice specialists, has been derived from observing rice growing under conditions that are not ideal for the expression of the potential productivity of rice.

There is a synergy among SRI practices that was discovered empirically, and partly serendipitously, by Fr. Henri de Laulanié, S.J., in the early 1980s in Madagascar (see Origins of SRI). This synergy has been documented by factorial trials in 2000 and 2001. [note: page on Synergy among SRI Practices will include data from these factorial trials]