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Effect of nitrogen and crop management strategies on rice under water-saving cultivation techniques
Dissertation Abstract:
An evaluation of the impact of synergistic interactions of different N fertilization patterns (rate and application time), establishment methods (transplanting and direct seeding) and cropping patterns (seeding rate and sowing date) under alternate wetting and drying (AWD) irrigation on grain yield, water productivity and nitrogen use efficiency (NUE) of lowland Thai rice varieties were conducted. In the polyhouse experiments, selection of best suitable variety and establishment method along with optimum N fertilizer management maintained under AWD irrigation (-5 kPa soil water potential) were the key considerations for maximizing yield and NUE. Overall, RD57 performed better than Pathumthani 1. Split application of N was more effective for both of the tested cultivars than one basal application. Dry direct seeding resulted in better root characteristics at 120 kg N ha-1, whereas the same root traits were better at 90 kg N ha-1 under wet direct seeding. Transplanting had better root systems development at 60 kg N ha-1. Shifting crop management practices with interaction on N levels on yield, water productivity and NUE of rice under AWD irrigation and continuous flooding (CF) were evaluated in field experiments. Higher grain yield and water productivity were evident at 120 kg N ha-1 than 0 kg N ha-1. Seeding rates of 95 to 125 kg ha-1 provided better results in terms of vegetative and reproductive growth, grain yield, and water productivity. Rice grown under AWD resulted in statistically similar grain yield with rice maintained under CF, but there was 40-44% more water savings depending on seeding rates and 68% higher water productivity under AWD. Early sowing (10 and 20 November) with 120 kg N ha-1 had better plant height, tiller number plant-1, shoot dry matter, panicle number plant-1, and grain yield compared with late sowing (30 November). Likewise, AWD irrigation combined with 120 kg N ha-1 produced better yield with higher total water productivity compared with CF. Earlier sowing increased total water productivity (21%), agronomic efficiency of applied N (113%) and partial factor productivity of applied N (38%) than late sowing.