Effects Of Plastic Film Mulch And Straw Incorporation On Soil Nitrogen-transformation-related Enzymes In Maize-cropped Farmlands

In order to improve the status of natural hydrothermal condition of dry farming in Loess Plateau being not conducive to crop growth as well as low soil fertility, the study puts forward two measures including technology of whole covering on double edges and planting in catchment furrows, and straw incorporation to improve soil hydrothermal conditions in the area, increase the content of soil organic matter, and alleviate the status of low crop yield and poor growth condition. As an important part of soil fertility, the transformation, cycling and utilization efficiency of nitrogen are very important for crop growth. Study finds that plastic film mulch and straw incorporation promote mineralization of soil nitrogen, and soil nitrogen mineralization is mainly catalyzed by soil enzyme which is secreted by soil microorganism. The experiment focuses onmaking further explanation for nitrogen turnover processfrom high or low activity of several important enzymes related to soil nitrogen transformation in several important periods of maize growing, so as to make the cause of nitrogen turnover clear. This experiment conducted field trials in Yuzhong County, Lanzhou City, Gansu Province in 2014-2015 for two years, it set four treatments for arable land planted with maize, respectively bare land(CK), straw incorporation(S), plastic film mulch(M) and plastic film mulch + straw incorporation(SM), three groups repeat with random group. In important periods(seedling stage, jointing stage, heading stage, booting stage and mature stage) of maize growing, the study carries out dynamic measurement on protease, deaminase, dehydrogenase and urease, it also conducts measurement onsoil temperature, soil moisture content, microbial biomass carbon and nitrogen,p H value, organic carbon and total nitrogen of the experimental field. The following results are mainly obtained:1. Plastic film mulch and straw incorporation will increase soil enzyme activity. Specifically, under the four treatments of crop growing in the same period, the activities of soil protease, deaminase and dehydrogenase under the treatment of membrane mulching + straw returning to field are the highest, soil protease activity under the treatment of bare land is the lowest, and enzyme activity under the two treatments of plastic membrane mulching and straw returning to field is between these two treatments; as for urease, enzyme activity under the treatment of straw incorporation is significantly higher than that of membrane mulching treatment. In addition, the activities of protease, deaminase and dehydrogenase reach the maximum in booting stage of maize growing, and the maximum urease activity appears at the heading stage.2.Protease, dehydrogenase and deaminase three show extremely significantly positive correlation in maize growing period.3.Plastic film mulch will increase soil temperature obviously, Compared with no mulch, it increased soil temperature by 0.6-5°C,and increasing range in temperature will decline with temperature rise.4.On the whole, Plastic film mulch and straw incorporation will increase soil moisture contentin each period of maize growing, which will respectively increase by 6%-45% and 12%-29%.5. Plastic film mulch will reduce the p H value of soil, but straw incorporation has no significant effect on the p H value of soil.Plastic film mulch will make organic carbon content and total nitrogen content in soil slightly decrease, but straw incorporation will increase organic carbon content and total nitrogen content in soil. Microbial biomass carbon content under the treatment of straw returning to field is significantly higher than that of membrane mulching treatment, increased range is within 7.8%-124.5%; microbial biomass nitrogen content under the treatment of straw incorporation is significantly higher than that of plastic film mulch, increased range is within 7.9%-167.1%.In conclusion, plastic film mulch and straw incorporation can significantly increase enzyme activity related to soil nitrogen transformation, which is also closely related to its functions of increasing soil temperature, soil moisture content and soil microbial biomass carbon and nitrogen; it can be known that plastic film mulch and straw incorporation can also improve soil nitrogen mineralization rate, then high or low enzyme activity corresponds to soil nitrogen mineralization rate, which shows that we can indirectly reflect the speed of soil nitrogen mineralization rate through measuring high or low enzyme activity related to soil nitrogen transformation as well as effective correlation of various soil enzymes, and it is truly effective and feasible to state the specific causes of nitrogen turnover cycling from the perspective of soil enzyme.