Effects Of Straw Incorporation Approaches And N Rate On Yield Formation And Nitrogen Use Of Spring Maize

China is rich in straw resources,and reasonable straw utilization can effectively prevent environmental pollution caused by large-scale burning of straw.Improving the rate of straw returning to the field is conducive to improving soil quality,promoting crop growth and soil carbon sequestration and emission reduction.Straw contains a large number of macronutrients.Proximately,almost all the K2 O,the majority of P2O5 and a portion of N needed for crops can be offered under the complete straw return.Northeast China is an important food producing area in China.It is a potential nitrogen resource to produce a large amount of corn straw every year.In this study,based on a long-term of brown soil with biochar trial platform,five consecutive years(2015-2019)experiment was carried out to investigate the nitrogen turnover of soil-crop systems under rotary tillage with straw incorporation(RTS)and plow tillage with straw incorporation(PTS)combined with five N fertilizer rates(0,112,187,262 and 337 kg N hm-2).This study is to provide the scientific basis and support for the the suitable way of straw returning and the optimal N rate.The specific research contents and results are as follows:1.Effects of tillage with straw incorporation and N rate on grain yield and soil NbalanceThere were not a significantly effect of RTS and PTS on grain yield.The significant associations between grain yield and N rate were quadratic effects.Grain yield increased with N application rate.However,no further increase in grain yield was observed when the applied N exceeded 187 kg N hm-2.The optimal N input required for the highest maize yield fitted the exponential decline curve and could be reduced by 39%~48% using tillage with straw return.Nevertheless,PTS was more effective than RTS at lowering the optimal N application rate.PTS resulted in a higher level of unaccounted N from applied N fertilizer(38-81 kg N hm-2)than RTS.High N fertilizer input(> 262 kg N hm-2)combined with straw incorporation caused a high level of soil mineral N profit and substantially increased the unaccounted N(614-715 kg N hm-2).2.Effects of different tillage with straw incorporation and N rate on dry matter and Naccumulation and transferThere were no differences in the grain N accumulation under the two straw incorporation treatments.The recovery N efficiency and agronomic N efficiency were increased in RTS.The dry matter and N remobilization and contribution of dry matter and N remobilization to grain efficiency were increased in PTS.With the increase of N application,the grain N,the plant dry matter and N accumulation were increased.The highest contribution of N gain to grain N efficiency was obtained in the nitrogen application rate of 187 kg N hm-2.3.Effects of different tillage with straw incorporation and N rate on root distributionand water use efficiencyHigher levels of pre-sowing soil water storage and growing period field evapotranspiration,and lower levels of water use efficiency(WUE)and pre-sowing soil mineral N storage at a depth of 0-60 cm were obtained with the RTS treatments as compared to the PTS treatments.RTS treatments enhanced root length density(RLD)and root weight density(RWD)at a depth of 0-10 cm in Anthesis stage,and increased RLD and RWD at a depth of 40-60 cm and ratio of root length density(RLDR)and ratio of root weight density(RWDR)at a depth of 30-60 cm in wetter year,reduced RLD and RWD at a depth of 20-30 cm than those under PTS treatments.N addition promoted WUE,RLD and RWD at a depth of 0-10 cm compared to CK.The RLDR and RWDR were increased with 262 kg N hm-2.Overall,tillage with straw incorporation management and N rates markedly affected the soil water and nitrogen supply.This influenced grain yield indirectly by further mediating root traits with consequences for the pre-and post-Anthesis shoot N uptake of maize.4.Effects of different tillage with straw incorporation and N rate on soil enzymeactivities and microbial communitiesCompared with PTS,the soil organic carbon,total nitrogen,available phosphorus,available potassium,β-glucosidase(βG),N-acetylglucosaminidase(NAG),acid phosphatase(APH)and microbial abundance were increased,while total phosphorus,total potassium,ammonium,nitrate and microbial alpha diversity were decreased in RTS.The activities of βG,NAG and APH were improved in RTS with 187 kg N hm-2.The bacterial and fungal abundances in RTS with 187 kg N hm-2 and RTS with 337 kg N hm-2 were 1.27-27.51 times higher than those in the rest treatments.However,the bacterial and fungal alpha diversities were enhanced in PTS with MN 187 kg N hm-2and PTS with no N application compared with other treatments,respectively.Proteobacteria and Basidiomycota were the predominant phylum for respective bacterial and fungal communities.Soil water content and penetration resistance contributed more to the soil enzyme activity and microbial community than other soil properties investigated,whereas the βG and APH activities played the same roles in bacterial and fungal abundance.Overall,plow tillage with straw incorporation enriched soil microbial community structure,promoted plant N uptake and improved WUE and grain yield under low N applied.