Numerical Simulation Of Atrazine Transport In Soils Under Drip Irrigation And At Field Scale

Pesticides are indispensable in modern agriculture. They are highly beneficial to corps being grown and play an important role in improving the production and safety of foodstuff. But on the other hand, the use of pesticides has caused environment concerns. The hazards of pesticides with regard to public health and the environment have been recognized for some time. Traces of pesticides are found in groundwater, lakes and coastal waters. These traces may have a strong impact on aquatic ecosystems and/or on the quality of drinking water supplies. Atrazine is one of the most frequently detected herbicide in groundwater throughout the world. In China, it is widely used in summer maize in the north and northeast of China, and is a potential contaminant agrochemical to groundwater. With the development of agriculture in China, water saving agriculture and ecological agriculture must be put into practice. In the Chinese Crop Protection Policy, the following important strategic objectives for the use of atrazine were formulated: reduction of dependency, the use and the transfer of atrazine to groundwater, surface water and air. This thesis reports on a study of atrazine leaching through soils in agricultural areas. The study comprises three aspects: (1) physical simulation and numerical modeling of atrazine transport in soil from trickle irrigation (2) spatial variability of atrazine leaching in soils at field scale under infiltration-redistribution or agricultural meteorology by numerical simulation (3) an upscaling numerical method to simulate unsaturated flow in horizontally heterogeneous soils at large scale under flood irrigation and evaluation of a power averaging technique of effective parameters on simulation of atrazine leached in soils at field scale. Obviously, from the viewpoint to quantitatively describe the transport mechanism of atrazine in soils, it was very important both in theory and in practice to carry out the research on numerical simulation of spatial and temporal distribution of atrazine in soils under trickle irrigation and of risk assessment of atrazine leaching through soils at agricultural field scale.In chapter 1, firstly, the main target and its significance of this paper were addressed in detail, secondly, we briefly reviewed the previous study about atrazine transport and transformation, and the literature with a focus on numerical simulation of pesticide leaching under drip irrigation and of atrazine transport at field scale because much information was available in the literature about atrazine transport through soils, lastly, based on the reviewed literature, the objectives and technical procedure were made for this study.In recent years, the use of chemigation has become a method to apply pesticides directly to the plant root zone through trickle irrigation systems. We, therefore, studied the spatial distribution of atrazine in soil under chemigation in chapter 2. The distribution of atrazine in a sandy loam soil was monitored in a drip chemigation experiment and numerical simulations were conducted. In addition, adsorption and degradation parameters of atrazine on the test soil were obtained by batch equilibrium and batch incubation experiments. HYDRUS-2D software was used to simulate the moisture movement and atrazine transport in the soil. The mathematical model considered unsaturated, non-steady flow in asandy loam and taking into account adsorptive and degradable herbicide. Freundlich equation and first order kinetic equation were used to describe the adsorption and degradation of atrazine respectively. Based on the observed data obtained from a trickle chemigation device to the fan-shaped soil box and result of the sensitivity analysis, the numerical model was validated and it was shown that the numerical simulation of atrazine dynamics in the soil was most sensitive to Freundlich adsorption parameters. Then the mathematical model was used to analyze the effects of different initial water contents and different application rates on the spatial distribution of moi...