Effects of Delayed Nitrogen Fertilizer Application on Sink Source Characteristics, Dry Matter Accumulation and Grain yield of Machine-Transplanted Hybrid Indica Rice in Upper Reaches of the Yangtze River

Purpose To determine the sink source characteristics, dry matter accumulation of machine-transplanted hybrid indica rice as affected by delayed nitrogen (N) fertilizer applications and its relationship with grain yield.

Method Field experiments, control treatment (CK), conventional fertilization (N₁) and delayed nitrogen fertilizer application (N₂, N₃, N₄) were conducted by using two hybrid indica rice varieties Yuxiang 203 and Yuyou 7109 under machine-transplantation condition. Grain yield, leaf area index (LAI), grain-leaf ratio, dry matter accumulation and crops growth rate were measured in this study. Results Compared with CK, N fertilizer treatments significantly increased panicles and spikelets per panicle, and consequently improved grain yield. The grain yield of different N fertilizer treatments showed that N₄>N₃>N₁>N₂. Compared with N₁, delayed N fertilizer applications decreased LAI in heading stage, and with significant reduction of LAI for Yuyou 7109. Compared with N₁, ratio of spikelet number to leaf area, ratio of filled grain number to leaf area and ratio of grain weight to leaf area of delayed N fertilizer applications (N₄) were increased by 10.2%, 25.0% and 29.3% for Yuxiang 203, and by 17.4%, 18.5% and 19.2% for Yuyou 7109, respectively. Compared with N₁, delayed N fertilizer applications (N₄) lowered dry matter accumulation before flowering, but increased biomass production and photosynthetic material production quite higher after flowering, which owed to higher crop growth rate after flowering.

Conclusion Delayed N fertilizer applications (N₄) controlled biomass production before flowering, increased crop growth rate and dry mater accumulation after flowering, improved grain-leaf ratio, increased spikelets per panicle, and thus, improved grain yield of machine-transplanted hybrid indica rice.