Growth Performance of Rice Under Different Water and Nitrogen Management

The present global water crisis threatens the sustainability of irrigated rice production as the demand for available water from urban and industrial sectors is likely to receive priority over irrigation for agriculture. It may necessitate the adoption of rice production practice that reduces water input without impairing yield. Besides water, nitrogen (N) is also an important factor, which often interacts with water and influence rice growth. The study was undertaken in a series of five greenhouse experiments, to determine the effects of water management on rice growth and N uptake efficiency and to evaluate N fertilizer management on growth, yield and N use efficiency of rice grown under different water management. The three water management treatments studied were flooded, non flooded (NF)-saturated and NF-field capacity, whereas the N management practices evaluated were N rate, source, split and placement. iii Experimental results showed that rice growth , grain yield, dry root biomass, total root length, root length density, plant N uptake and N fertilizer recovery were not significantly different between flooded and NF-saturated conditions, but were significantly lower under NF-field capacity condition. Grain yield was 57.6 and 54.4% lower under NF-field capacity than flooded and NF-saturated conditions, respectively. A higher grain yield and plant N uptake response to N application rate was observed under flooded and NF-saturated than NF-field capacity condition. The estimated N rate for maximum grain yield was 99, 105 and 126 kg ha-1 for flooded, NF-saturated and NF-field capacity conditions, respectively. Nitrogen use efficiency decreased with the increasing N rate, and was significantly lower under NF-field capacity. Results also indicated that urea alone was the most suitable N source for flooded rice . However, for NF-saturated condition, the use of polymer coated urea (PCU) or combined application of urea and compound fertilizer was more superior for grain yield and plant N uptake than urea alone . The 40/30/30 split applied during early tillering, active tillering and panicle initiation stages ensured adequate tillers and panicles which led to increased grain yield, plant N uptake and N use efficiency of flooded rice. All the three splits N treatments performed equally good and significantly better than the two splits, under NF-saturated condition. Grain yield and plant N uptake was low and not significantly affected by N split under NF-field capacity condition. The different methods of N placement iv tested did not significantly affect grain yield, plant N uptake and N use efficiency under all water management treatments . These findings suggest that rice can be grown under continuous NF-saturated condition without significantly affecting yield. However, adjustment in the N management practices especially the rate, source and split is necessary to improve N use efficiency and yield of rice grown under NF-saturated condition.

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