phosphorus, and pesticides. The model considers the effects of crop planting date, irrigation, drainage,
crop rotation, tillage, residue, commercial nitrogen and phosphorus applications, animal waste
applications, and pesticides on pollutant movement. The model has been used to predict the movement
of pesticides (Zacharias et al., 1992) and nutrients and sediment from various combinations of land uses
and management (Knisel and Leonard, 1989, Smith et al., 1991).
EPIC (Sharpley and Williams, 1990) simulates the effect of management strategies on edge of
field water quality and nitrate nitrogen and pesticide leaching to the bottom of the soil profile. The
model considers the effect of crop type, planting date, irrigation, drainage, rotations, tillage, residue,
commercial fertilizer, animal waste, and pesticides on surface and shallow ground water quality. The
EPIC model has been used to evaluate various cropland management practices (Sugiharto et al., 1994;
Edwards et al., 1994).
NLEAP (Follet et al., 1991) evaluates the potential of nitrate nitrogen leaching due to land use
and management practices. The NLEAP model has been used to predict the potential for nitrogen
leaching under various management scenarios (Wylie et al., 1994; Wylie et al., 1995).
PRZM (Mullens et al. 1993) simulates the movement of pesticides in unsaturated soils within
and immediately below the root zone. Several different field crops can be simulated an up to three
pesticides are modeled simultaneously as separate parent compounds or metabolites. The PRZM
model has been used under various conditions to assess pesticide leaching under fields (Zacharias et al.,
1992; Smith et al., 1991).
WEPP (Flanagan and Nearing, 1995) simulates water runoff, erosion, and sediment delivery
from fields or small watersheds. Management practices including crop rotation, planting and harvest
date, tillage, compaction, strip cropping, row arrangement, terraces, field borders, and windbreaks can
be simulated. The WEPP model has been applied to various land use and management conditions
(Tiscareno-Lopez et al., 1993; Liu et al., 1997)
DRAINMOD (Skaggs, 1980) simulates the hydrology of poorly drained, high water table soils.
Breve (1994) developed DRAINMOD-N, a nitrogen version of the model to evaluate nitrogen
dynamics in artificially drained soils. The DRAINMOD model has been used to predict pollutant losses
associated with various drainage management scenarios (Deal et al., 1986).
BARNY (Vermont NRCS, 1985) is a spreadsheet model that estimates total phosphorus
losses from dairy barnyards and estimates phosphorus loads entering waterways. Other similar models
include STACK, PHRED, and MILKHOUSE. These models have had limited use.
SWRRBWQ (Arnold et al., 1990) simulates the effect of agricultural management practices
such as crop rotation, conservation tillage, residue, nutrient, and pesticide management; and improved