Research On Movement Of Soil Moisture And Salinity In Cotton Field Of Drip Irrigation Under Mulch In Northern Xinjiang

Since the application by drip irrigation technology in Xinjiang Shihezi Nong Bashi 121 groups to be successful, then got a large area of promotion. Because of drip irrigation under mulch by small scale to meet the growing needs of the crop, the surface soil salt was leached to lower, over time, the salt slowly accumulated in the soil, which caused the soil salt accumulation phenomena. Different soil, planting patterns and planting years had different effects on the distribution of soil salinity, and because of the special geographical environment in northern Xinjiang of scarce rainfall, strong evaporation, winter lasted about half a year, strong winter freeze-thaw cycles and evaporation during spring had a big influence on the distribution of soil moisture and salinity. In order to explore the spatial distribution law of soil moisture and salinity in the non-growth period of the northern Xinjiang, and the soil moisture and salinity migration rule under the condition of freezing and thawing in winter, Xinjiang uygur autonomous region "twelfth five-year" major subject was combinated in this paper, through laboratory and field experiments combined method, the soil moisture and salinity distribution and migration law were explored. Preliminary results of this study are as follows:(1) In the beginning of growing period, the soil moisture and salinity presented a redistribution rule after the soil freezing and thawing cycles: In 0~100 cm soil layer, with the increase of soil depth, the average soil moisture content and salinity content showed a trend of decreasing after increasing. Below 40~60 cm layer, the mean salinity content gradually decreased with the increasing depth and the greater the soil depth, the greater declining rate.The salinity content was higher which closed to drainage ditch in the cotton field, and the majority of its adjacent to the area, whose soil salinity content was low, so setting up salt drainage ditch was advantageous to improve the cotton fields.(2) For long-term using the technology of drip irrigation with mulch in cotton fields, soil salinity gradually accumulated in 20~80cm soil layer. After a growth period, the soil moisture content of layers in October had a tendency to reduce relative in March’s, in addition to the surface(0~5 cm), and presented an increasing trend except 0~20cm layer. The 0~20 cm soil belonged to the saline soil, 20~40 cm soil belonged to light saline soil, 40~100 cm soil belonged to moderately saline soil in March. 0~20 cm soil belonged to the saline soil, 20 ~100 cm belonged to salinization soil in October. After the influence of people in the growing period, made the salinity content increase in 20~100 cm layer, but did not have a significant impact on the distribution of deep soil salinity.(3) After a growth and thawing period, the soil moisture and salinity content of layers in the second year in March relative to the first year in October had a lower trend.In the second year in March, the soil salinity content of layers relative to the first year in October, in addition to the 20~80 cm layer, there were increasing trends. Relative to the first year in March, in addition to the 40~60 cm layer, the soil salinity changed little, but the rest of the soil layer increased. For 40~100cm soil layer, after a year, soil moisture and salinity content changed little.(4) The temperature had much effect on the soil temperature. In the whole process of freezing and thawing, the changing trends of soil temperature were basically identical, with the increase of soil depth; the soil temperature was increase with the decrease of the first. The most deep frozen soil was 80 cm. In the early stage of the freezing, with the increase of soil depth, the soil moisture content showed an increasing tendency. The soil moisture in the form of a non-solid was mainly concentrated in 40~100 cm soil layer, soil salinity mainly distributed in 80~100 cm soil layer. In the freezing period, the soil moisture under the influence of minus temperature, started to freeze from the surface to the deep, soil moisture moved from the non-frozen layer to the frozen layer, and so was the salinity. With the increase of depth, the soil moisture of layers first increased then decreased and then increased, and the salinity content was first decreased and then increased. In the melting period, salinity content in 10~80 cm layer changed little, and salinity was mainly accumulated in 80~100 cm layer.(5) During the freezing and thawing, the minimum average salinity content appeared in2007 plots in the cotton fields with different planting years. The overall trend was that with the increase of planting years, the salinity content first decreased, then increased, and remained unchanged at last in different fields. Experimental field soil formed a relatively stable salinity accumulation zone on the vertical direction, and the position of the salinity accumulation zone changed with time. Namely in the freezing and thawing process, with the increase of planting years, the salinity accumulation zone moved from surface to the deep soil layer.(6) For different gradient of salt drainage ditch, with the time going, salinity in the salt ditch showed a tendency to increase gradually, between the lines and emitters at the head of the salt showed a trend of first increase and then decrease. With the increasing of depth,between the lines and emitters at the head of the salt showed a trend of first increase and then decrease, the maximum value of the lines and emitters was at the 80 cm. The soil salinity under the mulch was obviously moved from emitters to the bare salt ditch. The soil salinity below the emitters moved downward and formed a desalination region. The soil salinity under salt drainage ditch moved upward on the effect of evaporation, and salt accumulation area formed near salt ditch. Near the salt drainage ditch slope exhibited an approximately horizontal or oblique convergence characteristics.