| In order to improve the water use efficiency of dry farmland in northern China and explore the prospect of degradable plastic film application,the experiment uses 4 different types of film mulching patterns were set up for continuous fixed-point common plastic film mulching（P）,water-permeable plastic mulching film（SS）,biodegradable plastic film mulching（SW）and light degradation mulching（G）,with unpaved cover（CK）as the control,which based on Dongyang Agricultural Sciences Academy in Shanxi Province from 2015 to 2017.It studies the effects of different types of plastic film mulching on ecological effects of maize farmland,which includs soil hydrothermal activities,changes of enzyme activities,water and nitrogen use efficiency,maize yield and the phenomenon of residual film degradation and so on.The results show that:（1）Plastic film coverage can significantly increase soil temperature in the root zone of 0-25cm in maize seedlings.The temperature of SS,G,SW,and P treatments were 3.9,4.7,3.1,and 5.9°C higher than the CK respectively at 5 cm soil surface,and the temperature difference between day and night among each treatment was obvious.The temperature difference between day and night of P treatment was up to 35°C and the effect of heat preservation was:P>G>SW>SS>CK.The temperature range of 15cm at the seedling stage was 12-33°C.The average daily temperature of the SS,G,SW,and P treatments were 5.7,5.8,5.4 and 6.5 higher than CK respectively.The soil temperature at the subsurface 25cm was much smaller,which range was12-24.5°C.The average daily temperatures of the SS,G,SW,and P treatments were 4.1,5.2,6.7,and 6.0°C higher than CK.The mulching can be significant improve the soil water content in the 0-300cm soil depth in each growth period of maize and the soil water storage in the 0-60cm root range,and the SS and SW treatments had best conservation effects of water and nutrition.The average water content of the four film mulching treatments in the 0-300cm section was 1.37-31.98g/kg higher than CK,and the soil water storage in the range of 0-60cm showed a trend of“W”,which showed seedling stage,tasselling stage and harvest period were three peak periods,while the jointing stage and the filling stage were two low peaks,but the water storage performance of the treatments during different growth periods in different years was different,and was obviously affected by atmospheric precipitation.（2）The mulching of film can promote the growth and development of the plant and increase the yield of the crop.The maize plant height and yield under four mulching treatments were significantly higher than the CK.By the corn harvest,the plant height of the film-mulched corn was 33.67-41.33cm higher than the CK,and the yield increased by 0.14-4.28 t/hm2.Three-year trials have shown that the effect of increasing production is better when there is more rainfall.The increase rates of SS,G,SW,and P treatments in 2015were 20.3%,0.1%,15.4%,and 8.8%,respectively;and the increase rates in2016 were 30.02%,25.26%,35.02%,and 24.05%,respectively;and in 2017the increase rates of SS,G,SW,and P treatments were 29.14%,24.33%,49.90%,and 31.90%higher than the CK,respectively（due to drought in2015 and normal rainfall in 2016 and 2017）.The yield increasing effect among the treatments was as follows:biodegradable plastic film>infiltrated plastic film>photodegradable plastic film>commom plastic film>non-film-coated control,which had the same phenomenon with the change of temperature and moisture conservation effect of plastic film.SW and SS had the best effect.（3）The mulching of plastic film changed the soil hydrothermal status and soil microenvironment,and had different effects on soil enzyme activity.Alkaline phosphatase and nitrate reductase under the four kinds of coating treatment were higher than CK in each growth period,while urease,catalase and nitrite reductase under the film were lower than CK.The activity of alkaline phosphatase was the highest at harvest,and the activity increase of SS,SW,P and G at 0-20cm was 26.0%and 28.2 respectively.%,25.3%,24.4%,showed as SW>SS>P>G>CK;soil nitrate reductase activity in the harvest period of SS,SW,P,and G was 70.8%,87.5%,and 45.8%higher than CK,respectively.12.5%.Among them,the SW and SS treatments had the highest alkaline phosphatase activity and nitrate reductase activity during the whole growth period of corn,and the soil microenvironment characterized was the best.（4）The mulching of plastic film changed the micro-environment of soil water and heat,and affected the accumulation and transfer of soil nutrients and the absorption of nutrients by crops.The test results showed that:the four kinds of mulching treatments all increased the content of alkali-hydrolyzable nitrogen in the soil and decreased the content of available phosphorus,total nitrogen and total phosphorus,but the total potassium content did not change significantly.The content of alkaline hydrolysis nitrogen at 0-20cm between treatmentsshowedSS>SW>P>G>CK;availablepotassiumcontent SW>SS>P>G>CK;organic matter content CK>SW>SS>G>P.The study on soil nitrate in 0-300cm soil layer found that the nitrate nitrogen content of soils treated with the progress of the growth period showed a continuous decrease in the total amount,a rapid decline in the surface layer and a gradual downward leaching trend.The rate of decline of nitrate nitrogen content in the 0-300cm soil in the period from the big bell-mouth to the bell-mouth period was faster,and the rate of decline in nitrate nitrogen content from the grain filling stage to the harvest period tended to be gentle.The nitrate content of soil under the four kinds of mulching treatment was higher than that of CK,and the degree of leaching in the lower layer was deepened.From the seedling stage to the jointing stage,the nitrate content in the 0-20 cm soil surface was the highest,showing the change of P>SW>G>SS>CK.The content of nitrate nitrogen was the lowest in 40-140 cm,and there were two high peaks under 140 cm.From the jointing stage to the harvesting stage,a significant change is the deeper infiltration of nitrate in the membrane treatment,and the peak content continuously shifts to the lower layer of the soil.The overall nitrate nitrogen content between treatments is expressed as P>SS>SW.>G>CK.（5）Plastic film can significantly increase the use efficiency of water and nitrogen of the maize.The maize grew well under four kinds of mulching treatments,and the crop water consumption was large while the soil evaporation was small.Therefore,the water use efficiency（WUE）was also higher than CK.Among them,the WUE of SS and SW treatments were significantly higher than the others（P<0.05）,followed by G and P,and it also indicated that the moisture use efficiency of the film under drought years was higher.By a comprehensive analysis of the three-year trial,the average WUE of SS,G,SW,and P treatments were 10.06,5.83,12.00,and 6.36(kg.mm-1hm-2)higher than CK,respectively;the average nitrogen utilization rate were 4.05%,2.76%,4.86%and 2.65%higher than CK,respectively.（6）Based on different comprehensive factors,which included soil water and heat conditions,corn growth and yield,changes of enzyme activity,basic nutrient and water and nitrogen use efficiency,and degradation of plastic film residues,etc.We selected the best type of film cover for the semi-arid area in Shanxi Province as biodegradable mulch（SW）,it had the most obvious effect to increase the temperature and maintain the soil moisture.The water and nitrogen use efficiency was higher,and the final yield was also the highest.Besides,it was also can be split and degraded under the action of soil microorganisms and reduce the"white non-point source pollution"of farmland.Therefore,the biodegradable plastic film（SW）can be applied to dryland corn in the future instead of ordinary plastic film,and at the same time it also can achieve the effect of relieving farmland residual film pollution.By continuously improving the ratio of materials and adding additives,the application prospect is broad.The research results have certain theoretical support and practical significance for the choice of plastic film species in Shanxi Province and other arid and semi-arid regions,and it also provide certain theoretical value for the development of organic dry farming. |
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