Effects of N application rates on grain yield and N-fertilizer utilization efficiency of succeeding direct-seeded rice in wheat-rice rotation system

ObjectiveThe present study was conducted to investigate effects of N application rates in wheat growing season on growth, grain yield and N-fertilizer utilization efficiency(NUE) of succeeding direct-seeded rice, in order to explore the optimal mode of N management in a wheat-rice rotation system in central China. MethodSplit block design was employed with three N application rates(0, 105 and 210 kg/ha, expressed as WN0, WN105, and WN210, respectively) in wheat growing season, and after harvest of wheat, each plot was divided equally into three small plots which were assigned to three N application rates(0, 90, and 180 kg/ha, expressed as RN0, RN90, and RN180, respectively) in succeeding rice season. Plant height, tiller number, leaf area index, aboveground biomass, grain yields and yield components of wheat and rice were recorded at different growth stages, respectively. N contents of straw and grain of wheat and rice at maturity stage were determined, respectively. ResultThe results showed that, N application at 210 kg/ha in wheat growing sea-son had significant influence on plant height, tiller number, aboveground biomass, grain yield and NUE of succeeding di-rect-seeded rice compared with other N application rates. Among all treatments, every index for WN210RN90 was higher, and overall the performance under WN210RN90 was better. When N was applied in both wheat and rice growing seasons, all treat-ments was ranked in order of total grain yield: WN210RN180>WN105RN180>WN210RN90>WN105RN90, especially total grain yield of system under WN210RN180, WN105RN180 or WN210RN90 was over 13.50 kg/ha. In view of wheat grain yield, WN210RN180 and WN210RN90(3.55 t/ha) were better than WN105RN180(2.79 t/ha). ConclusionN-fertilizer application in wheat growing season have a significant residual effect to the succeeding rice season. Therefore, in wheat-rice rotation system, N application rate in rice growing season should be reduced due to residual N-fertilizer effect of wheat season. Considering grain yield and NUE in both rice and wheat seasons, the recommended N application rates(WN210RN90) are 210 kg/ha in wheat season and 90 kg/ha in rice season in central China, this N application combination is optimal mode of N management in rice-wheat rotation system.