Opportunities to manipulate nutrient-by-water interactions in rainfed lowland rice systems

Water stress, accompanied by changes in soil aeration, severely limits rice productivity in rainfed systems. These factors affect nutrient availability. Nitrate (NO3) that accumulates in aerobic soil is rapidly lost through leaching or denitrification in flooded soil. Green manures can act as NO3 catch crops and legumes may gain additional N from biological N fixation. Direct seeding permits additional crops to be grown. Roots are commonly shallow in rainfed lowlands. It is not clear to what extent rice yields in rainfed lowlands are Limited by water, nutrients, and the interactions between them, over diverse soil types, cultural practices and seasonal conditions. Research must determine what really Limits root growth, water extraction and nutrient uptake. Some evidence suggests that manipulation of controlled-release fertilizer and root system development may be the key to optimizing nutrient release and capture in fluctuating environments. The potential for using strategic application of nutrients Co buffer water Limitation and stabilize yields must be examined. Models such as QUEFTS (Quantitative Evaluation of the Fertility of Tropical Soils) provide a potential framework for analyzing the effects of soil fertility and water availability on growth and yield of rice. (C) 1998 Elsevier Science B.V.