Conservation practice effects on phosphorus losses from Southern Piedmont watersheds

Conservation and conventional tillage systems were used on small, upland watersheds in the Southern Piedmont to determine P contributions to nonpoint-source water pollution. Six tillage/cropping systems were studied on three watersheds over a 10-year period. Each tillage/cropping system was repeated every 2 to 4 years over a range of conservation practices and related to both C and P factors of the USLE. Total P runoff losses varied from 0.1 to 4.0 kg ha−1 yr−1 and consistently related to soil loss within each tillage system, irrespective of watershed landscape and the conservation practice imposed, The soluble-P fraction, PO4-P, and total dissolved P increased dramatically from about 10% to 40% of total P as multiple croppping and the use of conservation tillage intensafied with respect to crop residue cover. Although higher concentrations of both soluble P and total P were usually associated with conservation tillage, total P losses declined 50% or more while soluble P losses were nearly equal to or less than those measured for conventional tillage. These reductions in total P were the result of lower runoff volume with conservation tillage.