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Rice is often considered one of the most protected commodities in the world and only about 7% of global rice production is traded on the international market. In this distorted market, the major producing countries may close their borders to trade during periods of perceived supply shortage, as happened in 2007 and 2008.

The relatively low solubility and availability of phosphorus (P) from indigenous phosphate rock could be enhanced by legumes in the acid soils of humid forest agroecosystems. Crotalaria micans L. was grown in a screenhouse without P or with P from triple superphosphate (TSP) and Malian Tilemsi Rock P. The P response of 20 cover crops was field-evaluated using TSP and Rock P. In both experiments, the fertilized cover crops were followed by upland rice without mineral N or P application. Mean rice grain yield and agronomic residual P-use efficiency were similar for both P sources. In the field, 1-year fallow treatment of Canavalia ensiformis (velvet bean) supplied with Mali Rock P gave the highest rice grain yield of 3.1 Mg ha 21 , more than 180% that of 2-year continuous unfertilized rice (cv. 'WAB 56-50'). Among continuous rice plots, 'NERICA 2' (interspecific rice) supplied with Rock P produced the highest yield (2.0 Mg ha 21), suggesting that 'NERICA 2' might have greater potential to solubilize rock P. Results indicate that when combined with an appropriate legume, indigenous rock-P can release sufficient P to meet the P requirement of the legume and a following upland rice crop in rotation.

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