Effects of the Different Nitrogen Levels on Yield,Nitrogen Utilization Efficiency and the Nitrogen Balance of Double-Cropping Rice in Paddy Field
A field experiment was conducted to study the effects of different nitrogen application levels on yield formation,nitrogen utilization efficiency and rice-soil nitrogen balance,using"Zhongzao 39"and"Tianyouhuazhan"as test materials.The results showed that nitrogen application significantly increased the residual inorganic nitrogen in the 0-40 cm soil layer,and the nitrogen form was mainly NH4+-N,when the amount of nitrogen application was higher than 180 kg/ha(early rice)and 200 kg/ha(late rice),respectively.Rice-soil nitrogen balance showed that,except for nitrogen fertilizer,other nitrogen input accounts for 48.7％-78.4％of total input of nitrogen,nitrogen output is mainly affected by nitrogen uptake of rice,the soil nitrogen residue and nitrogen loss.In a certain range of nitrogen application,it increased significantly with the increase of nitrogen application rate.With the increase of nitrogen application rate,the yields of early and late rice increased first and then decreased,it mainly increased rice yield by increasing the number of effective panicles and spikelets per panicle.Utilization rate of nitrogen partial productivity,nitrogen utilization rate of agronomy and nitrogen interdependent rate significantly reduced with the increase of N application,but nitrogen absorption utilization rate,apparent retention rate of nitrogen and nitrogen contribution rate showed on opposite trend.Rice yield and N application quadratic regression model showed that the best early rice and late rice N application were 163.4 kg/ha and 209.2 kg/ha.Therefore,the recommended N application rate of early rice and late rice were 163.4 kg/ha and 209.2 kg/ha in Hangzhou,Zhejiang province,respectively,which can achieve high yield and efficient nitrogen fertilizer.
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