Potential to improve N uptake and grain yield in water saving Ground Cover Rice Production System

The Ground Cover Rice Production System (GCRPS) is a promising technology for water-saving lowland rice cultivation. However, excessive vegetative growth and potential N shortages during reproductive stages might limit the grain yield potential, because all N fertilizer has to be applied before transplanting due to technical difficulties with later applications. A 10-year experiment was conducted, covering two experimental series, to evaluate the effects of controlled-release urea fertilizer and a nitrification inhibitor, as well as effects of combining organic manure and mineral nitrogen fertilizer. In the first experimental period (2003-2006), field trials included four treatments: (1) zero-N; (2) urea alone; (3) urea + nitrification inhibitor; (4) controlled-release urea. In the second period (2007-2012), the first two treatments were continued as before, and treatments 3 and 4 were replaced by either application of chicken manure alone, or a combination of urea and chicken manure. Compared to applying urea alone, controlled-release urea, or the combination of urea plus organic manure, significantly increased grain yield and nitrogen use efficiency, and enhanced the number of spikelets and the percentage of filled grains due to improved growth in the reproductive phase. Application of urea plus nitrification inhibitor did not enhance grain yield and nitrogen use efficiency because of high nitrogen uptake and biomass production in early growth stages and significantly lower N uptake at the later stages, which consequently also led to low spikelet numbers. Application of organic manure alone significantly decreased above-ground biomass production in early growth stages, and strongly reduced the number of productive tillers, indicating N shortages in the vegetative stage. Our results showed that, considering the present costs of controlled-release urea, the combination of organic manure with mineral N fertilizer is the most practical and most economical N fertilizer management for improving grain yield and nitrogen use efficiency, as well as the sustainability of water-saving GCRPS. (C) 2014 Elsevier B.V. All rights reserved.