Simulation of atrazine, nitrate, phosphorus, and potassium dynamics in unsaturated soils using the Hydrus software

Abstract

Higher crop yields are most often associated with an increase in the use of agricultural chemicals, such as fertilizers and herbicides. Optimal management requires that correct amounts of these chemicals be applied throughout the growing season, while in reality often excessive amounts are being used. Irrigation and rainfall may then cause leaching of these nutrients and herbicides through the soil profile to below the soil root zone, leading to contamination of groundwater and in some cases even acidification of the soil. An example is the excessive use of the herbicide atrazine, which is widely used in Brazil and throughout the world. This herbicide is one of the main organic pollutants in groundwater; many nutrients (nitrogen, phosphate and potassium) are for these same reasons potential soil and groundwater contaminants. Sustainable management requires optimal use of agricultural contaminants, which necessitates proper knowledge of crop requirements and an understanding of the physical and geochemical processes affecting flow and transport processes in the subsurface. Thus, the objective of this project is to experimentally and numerically study the dynamics of the solutes in the subsurface below maize (corn) cropped surfaces. Simulations will be carried out using the HYDRUS-2D and STANMOD computer software packages, which have been widely used for these types of problems. Specific objectives are: a) to obtain the transport parameters of nitrate, phosphorus, potassium and atrazine from experimental breakthrough curves using analyses based on equilibrium and non-equilibrium advection-dispersion type transport equations; b) verify if the laboratory parameters also hold for greenhouse conditions involving different soil solution and mineralogical compositions; c) evaluate atrazine two-dimensional transport in soils cropped with maize, while accounting also for possible atrazine degradation; and d) perform statistical performance tests to demonstrate the efficiency of the HYDRUS-2D simulations for actual greenhouse conditions using laboratory and other data. (AU)