| Over-use of N in the intensive irrigated rice system not only decreased the water use efficiency (WUE) and nitrogen use efficiency (NUE), but also resulted in increasing environment pollution. Coordination of water and nitrogen management for achieving a win-win situation that will realize both high grain yield and improved WUE and NUE has still to be concentrated. However, most of studies on nutrient management were conducted with single treatment, over short time, by in-house modelling and/or on the relationship between yield and WUE. Little effort has been devoted to study the interaction effect of water and nitrogen on grain yield, grain quality, resource use efficiency (WUE or NUE), and ecological environment. The experiments were conducted under field conditions with a drought-resistant variety Hanyou3and irrigating varieties (Yangliangyou6, Hualiangyou9313and Jinkeyou938). Treatments were arranged in a resplit-plot design with water treatments as the main plots, nitrogen treatments as the subplots, and cultivars as the sub-subplots. Water treatments included semi-dry cultivation, alternative wetting and drying and continuous flooding. The nitrogen fertilizer rates were0,108,148.5and189kg ha-1in2009and0,108,175.5kg ha-1in2010. The objectives of this study was to determine the interaction effect of N and water treatments on the development, grain yield, yield components, WUE and NUE of two types of rice cultivars. The study developed an appropriate combination of N and water management for the intensive irrigated rice system, which could realize a high yield with an efficient utilization of N and water. In addition, the critical physiological traits limiting high grain yield and high resource use efficiency were elucidated. The main results are as follows:(1) In this study, there were no significant differences in grain yield under semi-dry cultivation (SDC) in comparison with continuously flooded (CF) and alternate wetting and drying (AWD) water regimes, but rice under semi-dry cultivation (SDC) had higher WUE due to the reduction in water utilization (68%and58%for CF and AWD respectively). In addition, the high-yielding cultivars outyielded the WDR cultivar by20%in the same management conditions. It was concluded that high yield and high efficiency in this study could be achieved by selecting high-yielding cultivar, adopting the SDC water management and applying relatively less nitrogen fertilizer (less than108kg ha-1).(2) Under various N treatments, SDC and AWD could restrict the elongation of basal internodes and increase lodging resistance. In addition, SDC and AWD had higher radiation transmitting efficiency in the middle of canopy due to a compact plant type, which was beneficial to the transportation of carbohydrates from the stems to the panicles during grain filling.(3) In this study, the crop growth rate maximized from panicle initiation stage to full heading stage, followed by that from full heading stage to maturity, and it was lowest at tillering stage. The effects of N treatments on crop growth rates varied at different growth stages, with a positive linear relation at tillering stage but quadratic curve relation after panicle initiation. Crop growth rate after panicle initiation was highest at108kg ha-1treatment. SDC had a higher crop growth rate compared with AWD and CF. No significant interaction effect was observed between water and N treatments on crop growth rate.(4) Degeneration of secondary branches and the percentage of unfilled spikelets in the primary and secondary branches were lower in SDC and AWD treatment, which compensated for the lower panicle spikelets.(5) Grain filling of rice superior spikelets started15days earlier than inferior spikelets. In the relatively lower nitrogen treatments (0and108kg ha-1), SDC could promote the start of grain filling of inferior spikelets. There were no significant differences in grain filling rate among the three water treatements.(6) There was a lower partition of root mass in0-10cm soil and a higher partition in the soil deeper than10cm for the WDR cultivar compared with the high-yielding cultivar. WDR cultivar had lower root mass but higher root-shoot ratio than that of high-yielding cultivars. The amount of bleeding sap of WDR cultivar decreased more than that of irrigating rice cultivars. There were congruous effects of water treatments on root mass, root-shoot ratio and root bleeding sap.(7) WUE of SDC and AWD were1.11and0.92kg m-3, which were35%and12%higher than that of CF, respectively. Effects of nitrogen treatments on WUE exhibited a quadratic curve pattern. WDR cultivars had a10%lower WUE than that of irrigating cultivars. The N accumulations of SDC and AWD at maturity were7%and4%lower than that of CF. N accumulation increased significantly as N fertilizer rate increased. Irrigating rice assimilated29%higher N at maturity than WDR cultivars. N use efficiencies for grain production (NUEg) of SDC and AWD were11%and4%higher than that of CF, and irrigating cultivars had a higher NUEg by17%. Agronomy nitrogen use efficiency (AE) decreased as nitrogen fertilizer rate increased, and SDC and AWD had higher AEs than CF by59%and19%respectively. AE of irrigating cultivars was27%higher than that of WDR cultivar. |
PDF Full Text Request