Effects Of Straw Returning Patterns On Soil Organic Carbon,Nitrogen Content And Soil Enzyme Activity

Northeast area is an important main spring maize production area in China,which planting area accounts for about third of the country’s maize planting area.With the expansion of maize planting area and yield,straw resources have been increasing.Straw is rich in organic carbon,nitrogen,phosphorus,potassium,and other nutrients.Straw returning can supply or substitute chemical fertilizer to improve the problem of cropland nutrients loss,it is main approach to improve fertility condition of filed with spring maize cultivation in northeast China.The purpose of this paper is to study the changes of soil physical and chemical properties and soil enzyme activities in northeast spring maize area under the condition of different straw returning patterns,providing scientific basis for straw returning in this region.In an in situ field experiment with micro-plots conducted for 4 years(2016~2019),we set up straw(S0-straw removal;S1-straw mixed with soil;S2-straw buried in the soil)and depths of straw incorporation factors(D1-10 cm;D2-20 cm;D3-30 cm),totally nine treatments,to research the effects of straw returning patterns on soil organic carbon,nitrogen content and soil enzyme activity for two consecutive years(2018~2019).Results indicated that: 1.Incorporation depth(D)significantly affected soil organic carbon and total nitrogen contents at 0~10 cm soil layer.Across the same soil layer,S1 treatments increased soil organic carbon content by 10.57~19.49% under D1 and D2 of mixing conditions compared with S1D3 treatment,respectively.Soil organic carbon and total nitrogen contents at 30~40 cm soil layer under S2D3 treatment was respectively higher than those from S2D1 and S2D2 treatments.2.Soil ammonium nitrogen,nitrate nitrogen and mineral nitrogen contents were significantly affected by straw treatment(S),interaction(S×D)between straw treatment(S)and incorporation depth(D).S1D1 treatment increased nitrate nitrogen content at 0~10 cm soil layer,While decreased nitrate nitrogen and mineral nitrogen contents at 20~30 cm soil layer,respectively compared with S1D2 and S1D3 treatments.Across 0~40 cm soil layer,S2 treatments decreased soil nitrate nitrogen and mineral nitrogen contents under D1 and D2 of burying conditions compared with S2D3 treatment.3.Straw treatment(S),incorporation depth(D)and their interaction(S×D)significantly affected soil invertase and acid phosphatase activities.S1 and S2 treatments decreased soil invertase and acid phosphatase activities under D1 of incorporating condition compared with D2 and D3 treatments,respectively.Soil invertase and acid phosphatase activities at 0~10 cm soil layer under S1D1 treatment were respectively higher than those from S1D2 and S1D3 treatments.S2D1 treatment increased soil invertase,urease and acid phosphatase activities at the same soil layer compared with S2D3 treatment.4.Incorporation depth(D)very significantly affected soil water content at 0~10 cm soil layer.Compared with S1D2 and S1D3 treatments,S1D1 treatment increased SWC at the same soil layer.Maize yield was affected by straw treatment(S),interaction(S×D)between straw treatment(S)and incorporation depth(D).S2D3 treatment increased kernel per ear,100 kernel weight,maize yield in 2019 compared with S2D1 treatment.Correlation analysis of soil physical and chemical properties and soil enzyme activities presented that a very significant positive correlation existed between soil organic carbon and total nitrogen,nitrate nitrogen,mineral nitrogen contents and soil invertase,acid phosphatase activities at 20~40 cm soil layer.5.The principal component analysis(PCA)of soil physical and chemical properties and soil enzyme activities suggested that soil organic carbon,total nitrogen contents,invertase,urease and acid phosphatase activities at 0~20 cm soil layer under S1D1 and S1D2 treatments and soil organic carbon,total nitrogen,nitrate nitrogen contents,p H,invertase,urease and acid phosphatase activities at 20~40 cm soil layer under S2D2 and S2D3 treatments were improved at the condition of S1 treatments.S2D2 and S2D3 treatments improved soil chemical and physical properties and soil three enzymes activity at the soil layer of 20~40 cm compared with S2D1 treatment.