Response difference of various rice varieties to nitrogen application rate in rice planting area in Guangxi

【Objective】Effects of nitrogen application rate on different rice varieties and nitrogen utilization efficiency were studied to provide theoretical basis for breeding and using high nitrogen efficiency rice varieties.【Method】Four nitrogen application rates(0, 75, 150 and 225 kg/ha) were applied on six rice varieties in Guangxi.Rice yield, main agronomic characters, nitrogen accumulation were tested to calculate nitrogen utilization efficiency under different nitrogen application rates.Correlation between rice yield and nitrogen application rate were determined by regressive analysis.The nitrogen rate for the maximum rice yield, nitrogen agronomic efficiency(NAE) and nitrogen partial factor productivity(NPFP) were estimated.【Result】In the range of 0-225 kg/ha nitrogen application rate, the plant height of the six rice varieties increased with the increase of nitrogen application rate, but the relationship between the effective panicle, ear length, grain number per ear, seed setting rate, 1000-grain weight and nitrogen application rate showed inconsistent;the overall change trend of rice yield was to increase with the increase of nitrogen application rate.When the nitrogen application rate reached 225 kg/ha, the yield of the varieties increased slowly, except that Guiyefeng began to decline.Compared with the nitrogen-free block, the average yield increase was 35.92%-67.45%, the rank from high to low was Hengfengyou 777> Guiyu 11> Yexiangyou 3> Guiyefeng> Baixiangyou 139> Guiyu 9.The nitrogen uptake efficiency, NAE and NPFP of the six rice varieties showed a gradual decrease with the increase of nitrogen application rate;the contribution rate of nitrogen increased with the increase of nitrogen application rate, when the nitrogen application rate reached 225 kg/ha, the contribution rate of nitrogen increased slowly or even began to decline.Rice varieties showed different average nitrogen utilization efficiencies with 1.53 times difference between the high one(Hengfengyu 777) and the low one(Yexiangyou 3).The optimum nitrogen application rate for the six rice varieties to obtain the highest yields was 181.9-219.7 kg/ha, the NAE was 10.1-17.9 kg/kg, and NPFP was 30.6-41.9 kg/kg.【Conclusion】Rice varieties showed different nitrogen uptake efficiencies, Hengfengyou 777 and Guiyu 11 are screened as rice varieties with high nitrogen efficiency under this experiment condition.