Effects Of Film Mulching And Fertilization On The Reserves And Availability Of Straw Nitrogen In Soil

Straw returning is not onlyan important agricultural technique to improve the physical and chemical properties of soil,but also as aresource to provide nitrogen?N?for crop.Plastic film mulching?PFM?and fertilization are the important agricultural management measures,which affects the transformation of N in soil and plant system.However,the distribution and transformation of N in the soil and the ultilization efficiency of new added organic N have not been reported under the condition of PFM and fertilization.Therefore,this study has been carried on a micro-area in-situ experiment by adding the ¹⁵N labeled maize straw at the long-term Brown Earth Experiment Station in Shenyang Agricultural University since 2014.The experiment was designed with and without mulching as main plots and four fertilizer treatments as subplots.The treatments both with and without mulching conditions included:?1?no fertilizer?CK?;?2?N chemical fertilizer?N?;?3?manure?M?;?4?manure combined with N fertilizer?MN?.The samples of soil and crop were collected after autumn harvest every year by determining crop yield,and quantitatively analyzing the transformation and distribution of straw N in the soil-plant system and the distribution of straw N in aggregates of brown earth during the maize growth process,then examining the impact of PFM and fertilization on the availability of straw N to the maize growth.The main results showed as follows:?1?PFM accelerated the transformation and utilization of straw-derived N in soil.The application of PFM and organic fertilizer generally increased soil microbial biomass nitrogen contents,promoting soil microbial activities,then accelerated maize straw decomposition,and reduced the contribution of straw-derived N to total N in soil microbial biomass.?2?PFM promoted nitrogen released from microaggregates.After 540-day incubation,the N content in the microaggregates?<0.25mm?was the lowest under PFM condition.Nevertheless,without mulching condition,it increased graduallyin the microaggregates?<0.25mm?during the experiment periods,while it decreased gradually in the macroaggregates?>2mm?.?3?PFM was beneficial to the enrichment of straw-derivedN in the macroaggregates.During the experiment periods,the average content of straw-dervied N in soil aggregates of>2mm,1-2mm in mulching conditions was higher than that in non-mulching treatments,and the average straw-derived N contents of soil aggregates at 0.25-1mm,<0.25mm were lower than that of non-mulching treatments.?4?PFM and fertilization promoted the uptake and utilization of straw-derived N in maize stems,leaves and grains,and significantly increased the plant utilization efficiency of newly added N.Under the condition of PFM,the utilization rates of straw-derived Nwere 10.5-20.6%in the first year?2014?and 5%-9%in the second year?2015?.Without mulching,the utilization rates of straw-derived Nwere 4.6-17.9%in the first year and 4%-7%in the second year.Fertilization promoted the uptake and utilization of straw-dervied in plant roots,stems,leaves and seeds,increased the plant utilization rates of straw-dervied N,and reduced itsaccumulation in soil.The highest plant utilization and the lowest residue rateof straw-derviedNwas in the MN treatment.