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

Understanding the combined effects of tillage and straw incorporation on grain yield and nitrogen (N) fertilizer utilization is vital for sustainable agriculture in northeastern China. How various tillage patterns with straw incorporation affect soil N balance and optimal N rate for crop production remains largely unknown. A four-year (2015-2018) field experiment was conducted to assess the impact of rotary tillage with maize straw incorporation (RTS) and plough 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. In general, higher straw N uptake and lower N partial factor productivity, N use efficiency, 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. Overall, 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.