Opportunities to improve phosphorus efficiency and soil fertility in rainfed lowland and upland rice ecosystems

The use of improved germplasm and management to increase rice production in rainfed lowland and upland systems is discussed. Understanding of the mechanisms conferring P efficiency, particularly external efficiency through root-induced changes in the rhizosphere, is reviewed together with evidence for genetic variation in P efficiency in upland and lowland rice germplasm. The following areas for improving resource and input management are considered: P management under alternately wet and dry soil conditions; P fertilizer formulations for banding in highly-weathered soils; cumulative responses to P fertilizer, including interactions with biological N fixation by legumes; amelioration of subsoil acidity, especially by leaching down the effects of surface-applied lime; and the management of soil spatial variability. Areas for future research are given.