Water And Salt Migration In Soil Under Brackish Drip Irrigation Condition

Water is a scarce resource for the economic development of national and region's society. Nowadays, the arid water has become a factor restricting the national economy and the sustainable developments. Therefore, it is of vital significance to develop and use brackish water for irrigation. Brackish water drip irrigation is a new kind technique which has an effective usage of water with poor quality and can inhibit soil salinity. Drip irrigation has the function of taking off salinity, which means that the soil salt content under the water dropper is relatively low as the salts tend to be accumulated at the wetted front. Drip irrigation can provide moderate water and nutrient to the root of crop, which is in favor of plant growing and improving crop yield. This thesis studied a kind of drip irrigation technique to effectively restrain the salt for the south of Xinjiang, where there are some problems like extreme arid climate, serious soil secondary saline-alkalization, low efficiency and water shortage in agriculture.Tarim basin, located between Tianshan and Kunlun in the south part of Xinjiang Uygur Autonomous Region, occupies the national area of 63%. It is an extremely arid desert areas with an average precipitation of 17.4-42.8mm and an average evaporation of 1125-1600mm. The basin is a typical agricultural area, characterized by oasis irrigated water from Tarim River. The south of Xinjiang, these years, is adjusting the agricultural planting structure and developing features plant so to change the traditional cotton-growing too high with high investment but low yield. This thesis studied the water and salt movement in the condition of brackish drip irrigation by the way of combining the theoretical analysis with the indoor experiment. Special interests were focused on the effect of salinity on the water and salt distribution under different soil salt content. Field experiment of drip irrigation was conducted to measure the water content and electrical conductivity. The main research conclusions achieved are as follows.1. The water salinity has a much obvious effect on soil moisture in the vertical direction than in the horizontal direction as saline water is used for irrigation. Such an effect and the water moisture was found to be decreased gradually with the increasing of soil depth.2. To some extent, the effect of water salinity on soil moisture is restricted by initial soil salinity, which mainly occurs in the cope from surface to 20-50cm depth.3. Brackish drip irrigation, different from normal one, creates a larger variation of soil water content. This can be attributed to the re-distribution of salt.4. The soil moisture showed an obvious difference after stopping irrigation for 48 hours due to the different initial soil salinity. In general, brackish drip irrigation on higher salinity soil can achieve higher soil water content, providing sufficient water to crop. However, some after-effects of soil water migration in practical application can not be ignored.5. The salinity of the irrigation water has a similar effect on soil electrical conductivity as that on soil moisture content:A larger effect can be found in the vertical direction than in the horizontal direction. Soil electrical conductivity showed a weakening trend in the vertical direction. However, there are some differences due to the initial salt content. For example, the effect blow 60cm depth can be ignored in case of low initial salt content, but this effect can reaches deeper layers when salt content is high. The electrical conductivity varies with the soil depth in a negative exponential function and the soil surface reaches a largest salt content in the treatment of brackish drip irrigation.This study can provide further understanding of the water and salt migration in soil under brackish drip irrigation condition. The result achieved can be used to improve brackish drip irrigation in XinJiang Uygur Autonomous Regional, especially in the southern area.