Long-Term Effect Of Straw Returning On Soil N Balance,Nutrient Upake And Crop Yield Under Wheat-maize Double Cropping System

Nitrogen plays a vital role in the crop yield increase,while the excessive N inputs do not keep synchronous increase of grain yield but lead to waste of resources and sever environmental issues.The N overuse occurs widely in the wheat-maize rotation system in Guanzhong plain.Meanwhile,the huge amounts of wheat and maize straw are not fully utilized and returned to soil.Thus,it is of great importance to investigate the effects of long-term straw return and its combination with reduced N input on the soil N balance,crops productivity.The field experiments started from 2008 and consisted of diverse regimes of wheat and/or maize straw return,and reduced N usage in this rotation system.The soil N balance,crop nutrient uptake and grain yield were observed in 2015 and 2016.The main results were as follows:?1?Compared to the no straw return control,the straw return treatments could either increase or decrease the wheat and maize grain yield,however,N,phosphorus and potassium uptake in grain of wheat and maize were the highest in the wheat high stubble-maize chopped and subsoiling return?WH-MM?or crushed return?WH-MC?treatments.After the wheat-maize rotation season,significant greater amount of residue mineral N was accumulated in 0-200 cm depth in WC-MC and WN-MN treatments,however,less was remained in the WH-MC and WH-MN treatments,as well as lower accumulation in the deeper soil depth,implied less N leaching losses in the wheat high stubble treatments.The negative values of apparent soil N balance in WN-MN suggested relatively short of N in this treatment.The study highlighted the balance of fertilizer application of fertilizer and also the amendment of straw return with N fertilizer,which would help to minimize the nutrient losses and reduce environmental pollution,as well as enhance the nutrient uptake and crop yield.?2?Under wheat high stubble return and maize straw crushed return,the grain yield of wheat and maize was slightly increased in treatments with 15%N reduction in comparison with conventional N rate during the 2015 to 2016 growing seasons,while significantly yield losses were observed in the 30%N reduction treatment.The annual total uptake of N in grain of wheat and maize was significantly suppressed by 13.4%in 30%reduction treatment than control,whereas the N and K uptake in straw of wheat and maize crops were reduced by 43.4%and 19.4%,respectively.The nitrate accumulation in 0-200 cm soil profile was significantly decreased in the N reduction treatments,especially in the 0-120 cm depth.Moreover,the 30%N reduction treatment had the lowest N surplus around 9.9 kg ha^-1 in 200 cm profile after harvesting of wheat crops,indicating relatively insufficient N supply to soil in this treatment.Taken together,the results suggested that,with the presence of straw return,at least 15%of N fertilizer could be saved than conventional N practice.(i.e.the recommended N rates are127.5 kg ha^-1 for wheat and 159.4 kg ha^-1 for maize)Overall,our results suggested that the straw return of wheat high stubble and maize straw chopping could reduce the N losses,and additional 15%N fertilizer could be saved in the wheat-maize rotation system.The fertilizer N application rate of 127.5 kg ha^-1 for wheat and159.4 kg ha^-1 for maize was recommended at the basis of straw return in both crop seasons in this rotation system in Guanzhong Plain,when considering the N balance,N utilization and grain yield.