The System of Rice Intensifi cation (SRI) 91science, to enable farmers to provide optimal growing conditions for rice production
that is sustainable both ecologically and economically.
SRI and the High-Yielding Theory of Rice Production
SRI is defined as a set of basic management practices (Stoop et al, 2002; http://
ciifad.cornell.edu/sri) that includes:
- transplanting very young seedling (10–15 days old);
- rapid and shallow transplanting one or two seedlings with wider spacing (30 ×
30cm or 40 × 40cm); - practising alternate wetting and drying (AWD) during the vegetative phase (or
keeping the soil moist but not continuously saturated); - applying compost in preference to chemical fertilizer.
The SRI concepts developed by Fr. Laulaniè in the 1980s in Madagascar (Stoop et
al, 2002), have many similarities with an earlier production approach (Horie et al,
2005) called ‘High-Yielding Theory’ (HYT) (Matsushima, 1973; Table 4.1). HYT
was a yield-increasing strategy, researched and practised in some Asian countries,
but largely overlooked during the Green Revolution period.
The one feature that differentiates SRI and HYT is plant density. SRI strives
to increase yield by maximizing yield per plant, whereas HYT pursues the same
objective by increasing plant densities per hectare. In doing so, HYT did eventu-
ally pay some attention to root activity but this effort was focused on increasing
the number of aerenchyma mainly by genetic manipulation (Lee, 1980). The
rationale was to minimize lodging at later growth stages which was the most com-
mon problem for rice plants grown with HYT. Although there was evidence that
the main compound which influences plant growth and development through
root activity was cytokinin (Richmond and Lang, 1957), this useful piece of infor-
mation was largely ignored until recently. In the late 1980s it was assumed that
higher root activity can increase a plant’s physiological efficiency; but this concept
was mainly acknowledged as a future breeding strategy (Kumura, 1989). The rea-
son for not pursuing root activity was fairly obvious, i.e. the factors enhancing and
maintaining root activity at later growth stages were not fully understood and
explored; and so remained untouched.
Only recent research has corroborated Richmond and Lang’s (1957) earlier
findings that the highly efficient photosynthetic performance of super high-yield-
ing rice cultivars is largely due to the increased cytokinin content in their roots
(Shu-Qing et al, 2004), contributing to higher grain yield. In addition, it has also
been found recently that, by minimizing plant density by transplanting a single
seedling per hill, root quantity and cytokinin content are enhanced in the rice
plant at later growth stages. This results in increased grain yield per plant due to