Effects Of Water-heat Regulating With Drip Irrigation On Nitrogen Dynamics,Soil Enzyme Activities And Chinese Cabbage Growth In Solar-heated Greenhouse

At present,the research and application of thermal control of soil and water mainly revolves around effect of drip irrigation technology.there is few research on the effects of nitrogen application process.In addition,the irrigation water temperature changes can also cause the change of soil hydrothermal condition,thus affecting crop growth,nutrient uptake and yield.But only a small amount of research focused on the use of irrigation water temperature adjustment to improve cold rice growth conditions and production.So under the condition of drip irrigation,carrying out the study of soil hydrothermal condition changes to nitrogen migration and crop absorption process,revealing water and nitrogen regulation mechanism in the different soil water heat under the condition of drip irrigation,will provide basis for the establishment of heat and water conditions.Field experiments were conducted during two growing seasons of chinese cabbage in 2015 and 2016 in solar heated greenhouse to evaluate the influence of water-heat regulation under drip irrigation on the change of soil temperature,distributions of water and nitrate in soil,Chinese cabbage growth,nitrogen uptake and yield.In the experiments,Four regulating methods of irrigation water heating,mulching,irrigation water heating with mulching and control treatment and three nitrogen levels of 0,150 and 300 kg N·hm-2 were tested.During both growing seasons,the distribution of soil water and nitrogen contents and the activity of soil enzyme at different depths was determined.Meanwhile,physiological indicators of chinese cabbage such as plant height and dry biomass above ground were regularly determined.When the cabbage was harvested,the yield of chinese cabbage was recorded.The main conclusions of this study are as follows:(1)From the point of single irrigation process,the effect of only irrigation water heating on soil temperature is limited,and the combination of irrigation water heating and mulch can achieve better result and increase amplitude about 1-2 degrees.In period,the effect height of mulch on soil temperature can arrive at 30 cm;The effect of mulch mainly show at the early stage and seedling stage 10-30 cm soil layer daily average soil temperature can be increased by about 1.4?2.1 degrees;The effect of the combination with mulch and irrigation water heating show better in the later period and heading stage 10-30 cm soil layer daily average soil temperature can be increased by about 1?3 degrees.(2)Irrigation water heating can advance soil water flow to deep;Mulch can increase 0-40 cm each layer soil moisture content.Increasing N application rate can obviously increase each soil layer soil NO3--N content in the reproductive period;Irrigation water heating and mulch both can reduce NO3--N accumulation in soil surface;Under the condition of mulch,0-20 cm soil NH4+-N content increase significantly.Mulch can increase the 0-20 cm soil organic nitrogen mineralization about 5.7%?38.7%,and the combination with mulch and irrigation water heating have an influence on the 20-40 cm soil organic nitrogen mineralization rate.(3)Water-heat control measures under drip irrigation and N application mainly influence 0?20 cm surface soil urease activity;Soil urease activity enhance with the increase of N application rate;Mulch,irrigation water heating(keep in 30?35 degrees)and the combination with mulch and irrigation water heating can make 0?20 cm surface soil urease activity enhance by 12%?17%,8%?15%and 18%?30%.Mulch can make 0?20 and 20?40 cm soil layer soil asparagines enzyme activity enhance 50%?140%and 50%?180%times;The combination with mulch and irrigation water heating can make 0-20 and 20?40 cm soil layer soil asparagines enzyme activity enhance 60%?200%and 60%?180%times.At the heading stage,the soil urease activity positive correlation with soil inorganic nitrogen content;At the rosette and heading stage,soil asparagines enzyme activity positive correlation with soil organic nitrogen mineralization and soil inorganic nitrogen content.(4)Cabbage plant height has increased with the increase of N application,but the differences between treatment decrease gradually in the later;In the early,mulch can make the cabbage plant height significantly increase.Mulch can improve the quality of Chinese cabbage dry matter of aerial part and nitrogen uptake by improving soil hydrothermal condition and soil fertility,thus increasing production,and combined with irrigation water heating better.(5)In order to avoid thermal damage as a result of high temperature,under the condition of drip irrigation,greenhouse chinese cabbage sowing date in north China can be delayed about half a month.In order to achieve the effect of water saving and high yield,farmers can use mulch way at the early stage improving soil hydrothermal condition,to ensure seeding emergence and the growth of chinese cabbage;The combination way of mulch and irrigation water heating(keep in 30?35 degrees)can be used to improve the soil temperature,in order to avoid the low temperature impact on crop growth and yield formation.