Distribution Characteristcs Of Nitrogen In Soil Aggregates Under Plastic Film Mulching And Fertilization

Soil aggregates are the place of materials transformation and energy exchange.Soil function mainly depends on good aggregate structure.Plastic film mulching changes soil temperature and moisture and then improves the basic physical and chemical characteristics of soil,which leads to the increase in crop production.But this increase is at the expense ofexcessive soil fertility.Fertilization is one of the important measures to improve soil fertility under the condition of plastic film mulching.However,it is still not clear that the distribution of soil aggregates and their nutrients at soil profile under the condition of plastic film mulching and fertilization.Based on the long-term experiment of Brown Earth in Shenyang Agricultural University in Liaoning Province,this research investigated the effect of long-term plastic film mulching and fertilization on the distribution of nitrogen in different soil aggregates,so as to provide scientific basis and practical guidance for sustainable development of soil and sustainable development of agriculture.In this study,three fertilization treatments with or without plastic film mulching were chosen:nofertilization(CK),single application of nitrogen fertilizer(N2)and single application of organic manure(M2).Soil aggregates were divided into>2 mm,1-2 mm,0.25-1 mm and<0.25 mmusing with the dry-sieving method.And the contents and storages of nitrogen insoil aggregates were analyzed at soil profiles(0-20 cm,20-40 cm,40-60 cm).The main results were as follows:(1)Soil aggregates of 0.25-1 mm were the dominant size,accounting for 33.96%-47.97%of dried soil weight;those of<0.25 mm were less than 10%.Plastic film mulching significantly increased the proportion of 1-2 mm aggregates,but decreased that of 0.25-1 mm aggregates at surface soil(0-20 cm).Compared with no fertilization and single application of chemical fertilizers,the application of organic manure increased the content of total nitrogen in macro aggregates(>0.25 mm).(2)Soil total nitrogen was the mostly distributed in 0.25-1 mm soil aggregate(the storage of 1.02 thm-2),followed by 1-2 mm and>2 mm soil aggregates,least in<0.25 mm with an average proportion of 3.69%in total soil nitrogen.The application of soil organic manure in the surface layer(0-20 cm)increased the storage of total nitrogen in soil aggregates.The storage of total nitrogen in>2 mm soil aggregates was increased by 32.31%and that in<0.25mm soil aggregates decreased by 31.82%after the application of organic manure with plastic film mulching compared with no-mulching.The opposite effect of plastic film mulching was found in the treatments of no fertilization and single chemical fertilzer.(3)The storage of ammonium nitrogen in macro aggregates(>0.25 mm)was mainly accumulated at soil depth of 0-40 cm.Average20.02%and 20.49%of ammonium nitrogen were,respectively,distributed in>2 mmand 1-2 mm soil aggregates,about 25.89%-33.59%in 0.25-1 mm soil aggregates,only average of 9.25%in<0.25mm soil aggregates.The storages of ammonium nitrogen in soil aggragates were not significantly(P>0.05)affected by plastic film mulching and its interation with soil depth.The storages of ammonium nitrogen in different soil aggregates was increased after the application of chemical nitrogen fertilizer,but decreased after that of organic manure at 0-40 cm soil depth.(4)The storages of nitrate nitrogen in soil aggregates decreased with soil depths(except for N2 treatment under no-mulching).After the application of nitrogen fertilizer under mulching,it mainly accumulated in 20-40 cm soil layer and was lower 35.65%-42.63%at 40-60 cm than at 0-20 cm soil depth.Compared with no-mulching,mulching significantly(P<0.05)increased the storage of nitrate nitrogen in different soil aggregatesat soil surface of 0-20 cm,but the storage of nitrate nitrogen in different soil aggregateswas obviously(P>0.05)affected by plastic film mulching under no-fertilization and organic manure treatments at 20-60 cmsoil depth.All the results showed that large aggregates were the main carriers of soil nitrogen,and large aggregates had strong enrichment and physical protection to nitrogen.Plastic film mulching decreased the accumulation of nitrate nitrogen in soil aggregates at soil profiles mightly due to its effect on soil tempeturate and soil moisture and the uptake of nitrogen by crops.Long-term application of chemical nitrogen led to the abundant of ammonium and nitrate nitrogen in soil aggregates atsoil profiles.Plastic film mulching and organic manure increased high cropyield and was an effective measure to ensure the sustainment development of soil and agriculture.