Sir

Your News Feature about rice cultivation, “Feast or famine?” (Nature 428, 360–361; 2004), is a classic example of how the debate on a potentially interesting technique can be blurred by its opponents and proponents. In this case, proponents of the System of Rice Intensification (SRI) are reported to claim miracle yields of 15 tonnes or more per hectare, which opponents dispute. However, both decline to consider the location-specific conditions under which, for example, low yields in Madagascar (2 tonnes per hectare) were doubled or even tripled using SRI; these are not miracle yields but still considerable for poor farmers in marginal areas.

There is evidence that such an increase is closely related to better water management, for example non-flooded conditions during the vegetative growth phase of rice in Madagascar's highly reducing soils (J. F. Vizier et al. Agron. Trop. 45, 171–177; 1990). Iron toxicity is probably responsible for depressed yields under permanently flooded conditions in these soils. This could be a starting point in the better understanding of SRI. A closer look at the world's rice-growing areas could also reveal similar acidic soils that would potentially benefit from improved water management.

Even a moderate increase in rice yields (2–4 tonnes per hectare) as a consequence of reduced flooding cannot be maintained unless other crop-management practices are changed as well. For example, nutrient inputs would need to be adjusted to account for the removal of more crop nutrients with the harvest, and weed control will require more attention under non-flooded conditions.

Other factors, such as decreasing farm labour in many rural areas and increasing water scarcity, pose important challenges to rice ecosystems. Only when the entire crop management is geared towards these often location-specific conditions, may new management practices — SRI could be one of many — contribute to the United Nations' goal of reducing hunger and poverty by half in a sustainable way.