SIMULATION OF THE IMPACT OF AGRICULTURAL MANAGEMENT-PRACTICES ON CHEMICAL-TRANSPORT IN MACROPOROUS SOILS

A simulation model capable of describing preferential movement of wate r and pesticides in macroporous soils has been developed. The model as sumes a bi-continuum, with flow and transport in and between each of t wo coexisting pore domains (matrix and macropore). In each pore domain , water pow is assumed to obey Richards' equation and chemical movemen t is assumed to obey the convection-dispersion equation. Interdomain t ransfer of water and chemicals occurs under pressure and concentration gradients. The model incorporates features such as root water extract ion, rate limited sorption and desorption, and first-order decay. The macropore volume fractions are allowed to vary with space to accommoda te variabilities in soil propel-ties. The model can represent two-dime nsions, to simulate the impact of agricultural management practices, s uch as tillage, irrigation, cropping practice, and organic addition, o n pow and transport.