Tillage with straw incorporation declines the optimal nitrogen rate for maize production by affecting crop uptake,utility efficiency and soil balance of nitrogen

[Objective]In order to identify the effects of straw return with rotary or plow till and nitrogen(N)application rate on maize grain and straw yield,grain N uptake and N use efficiency(NUE),and soil N balance and to determine the optimal N fertilization rate for maize production under continuous straw incorporation with tillage which is vital for sustainable agriculture in northeastern China.[Method]A four-year(2015-2018)field experiment was conducted to assess the impact of rotary tillage with straw incorporation(RTS)and plow tillage with straw incorporation(PTS)combined with different N fertilizer rates(0,112,187,262,and 337 kg N ha-1)on maize yield,N uptake,soil N balance,nitrogen use efficiency,and optimal N rate.[Result]In general,higher straw N uptake and lower N partial factor productivity,NUE,and recovery of applied N in grains were obtained under PTS than under RTS.Moreover,grain yield and both straw and grain N uptake increased with the N application rate.However,no further increase in grain yield was observed when the applied N exceeded 187 kg N ha-1.PTS resulted in a higher level of unaccounted N from applied N fertilizer(38-81 kg N ha-1)than RTS.A high N fertilizer input(>262 kg N ha-1)combined with straw incorporation resulted in a high soil mineral N profit and substantially increased unaccounted N(614-715 kg N ha-1)over the four-year field trial period.The optimal N input required for the highest maize yield could be reduced by 35.0%-44.6%using tillage with straw return.Nevertheless,PTS was more effective than RTS at lowering the optimal N application rate.[Conclusion]The results of this short-term maize field study conducted in northeastern China suggest that the amount of N fertilizer input required for maize production could be reduced by using tillage with continuous straw incorporation.