Permanent vegetative buffers such as agroforestry and grass
buffers, grass filter strips, and riparian practices reduce non-point
source pollution (NPSP) from agricultural lands (Gilliam, 1994;
Udawatta et al., 2002). These environmental benefits are attributed
to physical, biological, and chemical changes in the soil and
vegetation. Improvements in soil porosity, water storage, and
infiltration influence water movement within the soil and thereby
affect NPSP losses from watersheds. Perennial vegetation such as
pasture, grass buffers, or tree buffers increase soil porosity compared
to row crop land under tilled or no-till management
Changes in soil bulk density and addition of
organic matter probably contribute to better soil porosity. Perennial
vegetation also promotes more vertical and horizontal roots that
persist longer than roots of annual crops. This may result in larger and
longer continuous pores extending to subsurface horizons.