Influence of nitrogen and weed management on the productivity of upland rice

Nitrogen and weeds are two important factors that influence the productivity of rainfed upland rice (Oryza sativa L.) in tropical Asia. A low recovery of applied fertilizer N in rainfed uplands is generally associated with high nitrate leaching losses and weed interferences. Field experiments Rainfed Upland Rice Research Station, Hazaribag, Jharkhand, India, to determine the response of upland rice to nitrogen applied at 60kg N ha(-1) as different forms of urea (single pre-plant application of controlled-release urea, single pre-plant application of urea supergranules, and split application of prilled urea with or without basal N) against no N application under three weed-control regimes (unweeded, pre-emergence application of butachlor at 1.5 kg a.i. ha(-1) supplemented with one single hand weeding or two hand weedings). The response of rice to applied N varied greatly among the three weed-control regimes. Across the different N treatments, the application of 60 kg N ha(-1) resulted in a grain-yield increase above the unfertilized control of only 0.24 Mg ha(-1) in unweeded treatments, whereas yields increased by 1.07 Mg ha(-1) when butachlor application was supplemented with a single hand weeding and by 1.28 Mg ha(-1) with two hand weedings. Among the weed-control measures, hand weeding twice produced highest grain yield in both years. The comparison of different forms of urea showed that a single pre-plant application of controlled-release urea resulted in average grain yields of 1.57 and 1.87 Mg ha(-1) compared to 1.32 and 1.30 Mg ha(-1) in the case of the recommended practice of split-applied prilled urea in the years 2002 and 2003, respectively. The highest agronomic N use efficiency of 15-20 kg grain per kg N applied and the highest apparent N recovery of 39%-45% were attained with controlled-release urea, suggesting that this N form is particularly beneficial for upland-rice cultivation under variable rainfall conditions, provided weeds are controlled.