Influence of Seeding Rate, Nitrogen Rate and Weed Regimes on Productivity and Nitrogen Efficiency of Dry Direct-Seeded Rice

High weed infestation and low nitrogen (N) recovery are among the major causes of lower yield in dry-seeded rice (DSR) compared with transplanted rice. The effects of N rate and planting density dynamics on rice productivity and N-use efficiency (NUE) have been extensively studied in transplanted rice. However, information on the combined impact of N rates, weed regimes, and crop plant densities on rice productivity and NUE is very limited in DSR systems. Attaining synchrony between crop demand and N supply is a key in optimizing the tradeoffs amongst environmental pollution, kernel yield, and profit. Experiments were conducted in 2012 and 2013 to assess the impact of weed regimes (partial weedy and weed-free), N rates (0, 100, 150, and 200 kg ha(-1)), and rice seeding rates (50 and 100 kg ha(-1)) on crop productivity, N efficiency indices, and synchronization between crop demand and N supply. The seeding rate of 50 kg ha(-1) was better when the sunlight was not a limiting factor. The application of 150 kg N ha(-1) produced higher yield-contributing attributes and grain yield (5.2-6.6 t ha(-1)) of rice than 100 (4.7-5.6 t ha(-1)) and 200 kg N ha(-1) (4.9-6.5 t ha(-1)). The highest physiological efficiency (40-53 kg grain kg(-1) N uptake by plants) was achieved at 150 kg N ha(-1). Partial factor productivity was higher in the plots applied with 150 kg N ha(-1) than with 200 kg N ha(-1). The best degree of synchrony between crop N demand and supply was achieved at 150 kg N ha(-1). The results of this study suggest that for harvesting better grain yield, DSR crop should be planted using a seed rate of 50 kg ha(-1) in combination with 150 kg N ha(-1).