M. NOSHADI - Department of Water Engineering, College of Agriculture, Shiraz University, Shiraz, I.R. Iran
F. FOROUHARFAR (HAMILTON) - Department of Water Engineering, College of Agriculture, Shiraz University, Shiraz, I.R. Iran
S. AMIN - Department of Water Engineering, College of Agriculture, Shiraz University, Shiraz, I.R. Iran
M. MAFTOUN - Department of Soil Science, College of Agriculture, Shiraz University, Shiraz, I.R. Iran

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 ۲,۴- 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. ۲,۴- D was applied at ۳.۵ kg a.i./ha, followed by two irrigation treatments in a completely randomized design with three replications. ۲,۴- D concentrations were measured during the growing season by obtaining soil samples from each plot through a ۱ m depth. The measured data showed a temporal reduction of ۲,۴-D concentrations in the soil down to a maximum depth of ۴۰ cm for both irrigation treatments. Total concentration of ۲,۴ -D in the soil profile ۸, ۱۳, ۲۳, ۳۰, ۳۷, and ۵۷ days after application for normal irrigation were ۱۸.۵, ۱۶.۳۶, ۱۱.۶۷, ۱۰.۴۷, ۸.۴۷ and ۳.۲ mg kg ۱, respectively and deficit irrigation showed ۲۰.۲, ۱۶.۷, ۱۱.۲۲, ۱۰.۰۵, ۸.۸ and ۷.۳ mg kg ۱, respectively for the same dates and soil depth. According to our study region, the half life of ۲,۴- D for ۰ ۱۰ cm and ۱۰ ۲۰ cm of soil depths in a normal irrigation level were ۷ and ۳۳ days and in a deficit irrigation level were ۹ and ۳۴.۶۵ days, respectively. The statistical parameters including RMSE, CRM and d were used to compare simulated with measured data. These parameters were ۰.۶۷, ۰.۵ and ۰.۸۷ for normal irrigation and ۰.۸, ۰.۶۱ and ۰.۸۸ for deficit irrigation. The LEACHP model simulations were in agreement with actual observations.

۲, ۴-D, Degradation, Pesticides, Irrigation, LEACHP