Optimization of nitrogen fertilizer application to irrigated rice

Abstract

The ORYZA_0 model was used to optimize fertilizer N application programmes for irrigated upland rice. The crop and soil input parameters for this model were derived from field experiments. Soil characteristics apparently influence these parameters. The response of the rice crop as found by numerical optimization represented the maximum attainable biomass calculated on the basis of radiation, crop parameters and soil parameters. The maximum simulated biomass accumulation was 23.6 tonha−1 at 325 kg N ha−1 in a highly fertile soil, whereas in a soil of low fertility status the maximum attainable biomass was 15.3tonha−1 at 200 kgNha−1. The optimum dose of N application in the dry season was computed to be l20kgNha−1. The timing of applications indicated that most fertilizer N should be applied before panicle initiation. At low N input levels (20–40kg Nha−1), results suggested to apply fertilizer N around panicle initiation. The optimization by ORYZA_0 did not suggest any basal application of N in these soils. A field experiment was conducted to test the recommended timing of fertilizer N application based on ORYZA_0. It was found that higher crop biomass, N uptake and grain yield of rice would be obtained at the optimum N application level of 120 kg Nha−1, if appropriate timings suggested by the model are used. This optimum N level is higher than the level of N used in existing practices now.