Study On The Regulation And Simulation Of Water And Salt Transport In Cotton Field Under Mulched Drip Irrigation Condition

Drip irrigation of cotton as a universal application of a irrigation in Xinjiang has been a long-term applications. But due to the lack of theoretical support for the application process, many places are still in a very extensive management situation without a proper and efficient irrigation system. Long-term application of the drip irrigation can also cause soil salinization problems. Drip irrigation can be a more efficient and sustainable technology through reasonable regulation of the water and salt. How to regulate the water and salt reasonably in drip irrigation? Study of this problem, especially in the rational development and utilization of water resources and ecological environment in arid areas of Xinjiang has important practical significance. Supported by the "eleventh five-year" governmental scientific supporting project. The study has been in a depth analysis about the drip irrigation of cotton by field experiments and numerical modeling techniques of three years, and the appropriate irrigation system has been made out.This experimental study is carried out in the key national irrigation station of Bazhou in Xinjiang. For clarity of the soil physical properties in the study area, particle-size analysis experiment and soil moisture characteristic curve experiment for a variety of soils have been done. To well know the meteorological characteristics of the study area, continuously observed meteorological datum in the field using self-recording tintype meteorological station WATCHDOG, the observation items included rainfall, temperature, and downward short-wave radiation of the solar, wind speed and so on. To analyze the underground water table and the quality changes, observed the underground dynamic water table using digital self-recording water level monitoring instrument and sampled the groundwater for water quality analysis.In order to study the regulation of different irrigation water and salt under the different irrigation ration, a detailed plan has been made in the growth and non-growth period of the cotton. Using the methods of field sampling and equipment monitoring to study the changes of water and salt. At different conditions of soil water-salt, monitored and studied the response law of emergence of seedling to water-salt of the soil using the emergence of seedling test, studied the response law of root distribution changes to water-salt of the soil by monitoring tests of sampling roots in the space, evaluated and discussed the impact of water-salt of the soil on the growth and yield of the cotton through the plant height, leaf area, dry weight and yield of the cotton gotten by continuous monitoring at different growing period.The two dimensional numerical model is developed for simulating the transportation of water and salt with the consideration of root growth and water absorption, in which the description for the moving ponded area boundary is improved under the dripping condition. The semi-discrete method is applied to the coupled equation set of Richards equation and solute convection-diffusive equation, resulting in the ordinary differential equations, the numerical solution is obtained with CVODE (a state-of-the-art ordinary differential equation solver), the numerical stability and calculate efficiency is improve. The model can be used for the long-term continual simulation of water-salt transportation. The scenario with different irrigation quotas, irrigation intervals and drip rates based on the conducted experiments are numerically analyzed by the model. Meanwhile the transportation and distribution of water and salt under different groundwater levels and the soil salty accumulation of five years under different winter irrigation(winter irrigation interval) were further investigated.Through three years of field experiments and model studies, based on the mulched drip experimentation and the simulation analysis, combined with the actual situation in the southern, a set of appropriate mulched drip irrigation system for water and salt regulation established in the growth and non-growth period of cotton has been made out. In the hope of cotton drip irrigation can be efficient and sustainable development.