Optimal nitrogen application rates on rice grain yield and nitrogen use efficiency in high,middle and low-yield paddy fields

Effects of different nitrogen application rates on grain yield of rice and nitrogen use efficiency in high, middle and low yield paddy fields in Hubei Province were studied. Field trials were carried out to investigate the optimum N application rate on rice cultivar,Liangyoupeijiu in paddy fields with different yield levels( high,middle and low),and to observe the effect law of different N application rates on rice yield and its components,N fertilization contribution rate,soil N dependent rate and N use efficiency. The results obtained in the 2011 field trial show that both high and middle yield fields have the highest rice grain yields under the treatment of N 180 kg / ha,with 10. 70% and 27. 23% yield increases respectively compared to the treatment of CK,while the highest yield in the low-yield field is acquired under the treatment of N 240 kg / ha,which is 44. 70% higher than that of the CK. Both high and low yield field spots achieve the highest rice grain yields under the treatment of N 180 kg / ha,with 12. 43% and 74. 19% yield increases respectively compared to the treatment of CK in 2012,and the highest yield in middle yield field spot is acquired under the treatment of N 240 kg / ha,which is 28. 80% higher than that of the CK. At some certain range,with the increase of the N application rate,the N agronomic efficiency and N physiological efficiency are increased,while the partial factor productivity is decreased. By the analysis of yield,yield components and N use efficiency,we conclude that the optimum N application rates are N 120-180 kg / ha in high and middle yield fields,and are N 180-240 kg / ha in low-yield fields. The optimum N applicationrate is in order,low yield field middle yield field high yield field.