Water Transformation Rules Of Mulched Drip Irrigation Using Isotopes In An Arid Region

Study on the rules of soil water transformation is of great importance to reasonable water resources utilization and to realize agriculture water-saving irrigation.In this paper,cotton field that in the Paotai Soil Improvement Test Station in Xinjiang Production and Construction Crops are taken as examples.Based on the stable hydrogen and oxygen isotopic tracing method and hydrological observations,combining with numerical simulation method in this study,soil water dynamics distribution characteristics in different grow stage of cotton and the isotopic compositions of precipitation,soil water,irrigation water and stem water are studied,besides,source of root water uptake and its contribution proportion are quantified.soil water numerical model is built with Hydrus-2D to discuss the process of soil water movement and SPAC continuum water flux in cotton fields under drip irrigation with the common style of one mulched with six rows in Xinjiang arid region.All the research contents reveal the law of soil moisture transformation in Xinjiang arid region cotton field.The main conclusion of this paper are as the following.?1?Along with the 0²20cm soil profile,soil water content gradually increase with the increase of depth.The soil water content change significantly within 60cm layer,while the soil water content in deep layer is relatively stable.The soil water content fluctuates significantly after a single irrigation or heavy rainfall affected by recharge and discharge.Both irrigations result in a significant response to soil water within a depth range from 0 to 30cm.The whole change trend of the soil moisture content at each growth stage is similar.?2?The local meteoric water line is expressed as?D=7.223?¹⁸O-0.620?n=8,R2=0.97?and the soil water isotopes fitting curve is expressed as?D=4.762?¹⁸O-31.587?n=76,R2=0.95?,which proves that the precipitation and soil water evaporated obviously.The soil water isotopes more enrich from 0 to 30cm,while the soil water isotopes more deplete below 170cm.The isotopes values of soil water present a trend of gradual depletion with the increase of depth.After a single irrigation,the stable isotope values of soil water from 0 to 60cm are significantly reduced.The stable isotope composition of hydrogen and oxygen in irrigation water is relatively stable during the study period.The stem water isotopes more enrich in bud stage than that in vigorous growth stages.?3?The innovation of this paper is to quantitatively calculate the utilization rate of different depth soil water in each growth period of crops by the IsoSource model.Results show that the main uptake depth of soil water in bud stage,blooming stage,boll stage and boll open stage are distributed in 0-30cm layer?78.2%?,30-60cm layer?31.9%?,60-110cm layer?32%?and 110-220cm?47.3%?,respectively.The main depth of soil water used by cotton gradually increases with the advance of growth stage.Roots water uptake depth adjust rapidly after mulched drip irrigation,which significantly increases the proportions of 0-30cm soil water utilization to cotton.The results also indicate the proper irrigation regime with low irrigation volume and high irrigation frequency can improve the efficiency of the agricultural water utilization in arid regions.?4?In this study,soil water numerical model is built with Hydrus-2D and calibrate with the experimental data.Results show that under periodic irrigation a divergent curved surface of zero flux shapes below the land surface 50⁷0cm deep.During the whole simulation period,irrigation is the main source of inflow water,accounting for 87.6%of the inflow water.More than 70%of the inflow water is consumed by cotton,while soil evaporation and deep percolation account for only 8.2%and 20.8%.The utilization efficiency of agricultural water is 85.2%.The simulation results suggest that current drip irrigation with the style of one mulched with six rows can effectively reduce invalid evaporation and deep percolation and improve the utilization efficiency of irrigation water resource.