Nutrient requirements in rainfed lowland rice

In rainfed lowland rice, nutrient status of soils is often poor, and response to applied nutrients is often unreliable. This paper seeks an improved understanding of these patterns of nutrient response, then considers likely approaches for increasing and stabilising yields of rainfed lowland rice in south and southeast Asia. At each of 78 locations across India, Bangladesh, Thailand, Indonesia and the Philippines during 1995-1997, three replicates of each of six treatments were established: (no fertiliser control (NIL), farmyard manure (FYM), phosphorus and potassium only (PK), application of nitrogen as well as P and K (NPK), a controlled-release formulation of N together with P and K (CR-NPK), and an all-nutrient dressing (ALL)). Combined analysis of variance and cluster analysis were used to examine the patterns of nutrient response. Yields obtained without applied fertiliser were not closely related to soil test values. The greatest nutrient response was to nitrogen, with NPK increasing yields from 2.25 to 4.00 t/ha on average. The effect of adding micronutrients was small, and PK was of little benefit unless N was added. But the magnitude of the N response varied substantially with water regime. We conclude that substantial yield gains are possible in rainfed systems with application of appropriate nutrients, especially if used in conjunction with cultivars suitably adapted to the target environments. (C) 1999 Elsevier Science B.V. All rights reserved.