Fertility and organic matter in submerged rice soils

Wetland rice systems in Asia make a major contribution to global rice supply. The system is also able to maintain soil fertility on a sustainable basis. The essential components of wetland rice culture comprise cultivation of land in the wet or flooded state (puddling), transplanting of rice seedlings into puddled rice paddies, and growing the rice crop under flooding. The land is dry or flood-fallowed during the turnaround period between two crops. Following these cultural practices, two or three crops of rice or rice with upland crops in sequence are grown. However, in the present context of increasing freshwater scarcity, there is a case to shift from the traditional way of growing rice to ways that are water-wise. In this context, it is crucial that the benefits of the wetland rice system on soil fertility and productivity are considered. This article examines the benefits of growing rice in flooded conditions on soil fertility and its maintenance. Research has shown that the wetland rice system (growing rice in submerged soils) has a great ameliorative effect on chemical fertility: largely by bringing pH in the neutral range, resulting in. better availability of plant nutrients and accumulation of organic matter. The article concludes that the benefits of growing rice using submerged conditions must be considered and weighed in the context of a likely shift to growing rice with water-management practices that are water-wise.