Application of a screening model to evaluate pesticide contamination in soil and groundwater for sustainable agriculture in Oman

In the recent years, agricultural activities in Oman have been increased signi ficcantly that has increased the use of pesticides. Consequently, soil and groundwater quality is likely to deteriorate. This chapter presents prediction of pesticide movement through the unsaturated zone to groundwater. This will help the decision makers in assessing the likelihood of soil and groundwater contamination in Oman under various land use practices. A model (PESTAN) based on the analytical solution of 1-D advective-dispersive-reactive transport equation is used to estimate the vertical migration of the dissolved organic solutes as well as for conducting initial screening assessment of the potential for contamination of soil and groundwater. PESTAN calculates the movement of organic chemicals with a linear isotherm, ficrst-order degradation, and hydrodynamic dispersion. Input data include the following: Soil, chemical, and management practice parameters. Data on Omani soil, climatic, and irrigation practices as well as chemical parameters of most common pesticides used are required for modeling. Reliable assumptions are made to compensate for missing data. The main objective was to model the top ten pesticides used in Oman for 5 years to calculate the time each particular pesticide would take to reach the water table that is estimated to be at 10-m underground surface. Three scenarios were developed, after selecting three variables which mainly contribute to pesticides’ fate: Recharge, soil texture, and application rate of pesticides. For each variable, maximum and minimum values were modeled to be compared with a base run describing the recommended conditions. The results suggest that the more the recharge and application rates, the faster the pesticides reach groundwater. In coarsetextured soil, the pesticides penetrate faster through the soil proficle. Overall, the simulations demonstrated that none of the ten pesticides is reaching the water table to a depth of 10 m within 5 years by assuming a single application, where application frequency is concerned. Reducing irrigation amount and increasing the organic matter content of the soil will help reduce groundwater contamination.