Effects Of Maize Straw Returned Depths Onsoil Organic Carbon Fractions And Enzyme Activities

Heilongjiang Province as a major grain producing areas,rich in straw resources.Due to the low level of commercialization of straw,especially straw burning also brought a series of environmental pollution problems,resulting in a lower utilization of straw.Many studies have shown that straw returned can improve soil organic carbon content,and deep straw returned is more beneficial to the accumulation of soil organic carbon,microbiological activity and soil enzyme excitation.In this study,the effects of different depths of straw on soil organic carbon and its components and soil enzyme activities were studied by net bag burial method,which provided the theoretical basis for straw returning to different tillage measures.The results showed that:(1)During the period of the return field,the decomposition rate of the surface covered straw was much lower than mix soil with straw,and the rate of decomposition in straw return 15 ~ 30 cm was the highest in each period.The variation trend of straw decomposition rate at the same depth was consistent,which showed that it was fast in the early stage,slow and stable in the later stage.During the period of the whole field,the total change trend of nitrogen,phosphorus and potassium release rate in straw was consistent,which was fast in the early stage,slow and stable in the later stage.After one year of straw returning,the release rate of nitrogen and phosphorus that the straw returned to 0 to 30 cm was greater than that of straw mulching and straw returning to 30 ~ 45 cm.The release rate of potassium that the straw returned to 0 to 45 cm was greater than straw cover.It is concluded that the nutrient release rate after the mixed application of straw and soil is greater than that of straw cover in the soil.Straw after a year of decomposition,the body of fiber,woody substances are reduced;straw cellulose with soil changes have a certain regularity,the deeper soil layer,the lower straw cellulose content.There is a certain correlation between the indicators that characterize the straw nutrient,and the prediction between the indexes can be carried out in the actual production.(2)Straw decomposition after one year,the results showed that: Soil organic carbon was grouped,variation of carbon content in each component was that heavy fraction organic carbon content was the highest,followed by free light fraction organic carbon content,and occluded light fraction organic carbon content was the minimal(P <0.01).Variation of carbon concentration in each component was that free light fraction organic carbon concentration was the highest,followed byoccluded light fraction organic carbon concentration,and heavy fraction organic carbon concentration was the minimal.Contrast one year of straw decomposition with 30 ~ 120 daysof straw decomposition,in different depths,the contents of total organic carbon and density group were increased in different degrees.When the straw was decomposed for 120 days,carbon content of each fraction of 15 ~ 30 cm deep was increase more than control.There was a significant correlation between soil TOC,HFOC and Occluded-LFOC.(3)The straw returned 30 ~ 120 days,comparing the period the change of soil microbial carbon and nitrogen in different soil,returning 15 ~ 30 cm microbial carbon content is the highest,comparing with other treatment have significant differences in different periods,surface coverage microbial nitrogen content in the highest,comparing with other treatment have significant differences in different periods;After 1 year of straw return,the content of soil microbial carbon and nitrogen with the soil layerincreased,which showed a tendency to decrease gradually,Comparing the change of soil enzyme activity in each period different soil,soil enzyme activity of straw surface coverage is higher,the soil enzyme activity trend of the seasons change was reduced after the first rise,straw returned urease peak appeared after 90 days,straw returned invertase peak appeared after 60 days.After 1 year of straw return,soil urease activity was lower than that before.The activity of invertase in soils was lower than that of straw for 30 to 90 days,and higher than that of straw for 120 days.Compared to contrast,straw returned significantly increased soil urease and invertase activity,and returning in 15 ~ 30 cm,the improvement of soil urease and invertase activity even more significant.Correlation analysis showed that the depth of the straw returned has significantly correlation to soil microbial nitrogen,soil urease,invertase soil temperature and soil water content.