Measuring and Simulating 2,4-D Residues in Silty Clay Soil Profile Under Two Water Regimes Using a LEACHP Model

The extensive use of pesticides in agriculture is compromising soil and water quality. One major concern is protecting water resources from contamination. The main objective of this research was measuring 2,4- D in a silty clay soil and simulating temporal transportation of this herbicide in soil using a LEACHP model, in a corn root zone field. 2,4- D was applied at 3.5 kg a.i./ha, followed by two irrigation treatments in a completely randomized design with three replications. 2,4- D concentrations were measured during the growing season by obtaining soil samples from each plot through a 1 m depth. The measured data showed a temporal reduction of 2,4-D concentrations in the soil down to a maximum depth of 40 cm for both irrigation treatments. Total concentration of 2,4 -D in the soil profile 8, 13, 23, 30, 37, and 57 days after application for normal irrigation were 18.5, 16.36, 11.67, 10.47, 8.47 and 3.2 mg kg 1, respectively and deficit irrigation showed 20.2, 16.7, 11.22, 10.05, 8.8 and 7.3 mg kg 1, respectively for the same dates and soil depth. According to our study region, the half life of 2,4- D for 0 10 cm and 10 20 cm of soil depths in a normal irrigation level were 7 and 33 days and in a deficit irrigation level were 9 and 34.65 days, respectively. The statistical parameters including RMSE, CRM and d were used to compare simulated with measured data. These parameters were 0.67, 0.5 and 0.87 for normal irrigation and 0.8, 0.61 and 0.88 for deficit irrigation. The LEACHP model simulations were in agreement with actual observations.