PHOSPHORUS MOVEMENT IN THE LANDSCAPE

Phosphorus movement in runoff often promotes algal growth in lakes. Th us, agricultural soils and management practices that enhance the poten tial for P movement must be identified. The main factors controlling P movement are transport (runoff and erosion potential) and source fact ors (surface soil P and method, rate, and timing of fertilizer and ani mal manure applications). Implementation of management that minimizes runoff and erosion will reduce P transport in runoff, although total a lgal availability can increase. The continued application of P has inc reased surface soil test P contents in excess of levels sufficient for optimum crop yields. Although increases in soil P have been related t o P enrichment of runoff in plot and watershed studies, information fo r given management systems still is needed to reliably quantify critic al soil B levels above which excessive P enrichment of runoff will occ ur. Clearly, P applications must be carefully managed, in addition to minimizing transport potential, to efficiently reduce P movement in la ndscapes. This may be achieved with regular soil testing, P incorporat ion, application during times of low runoff probability, and irrigatio n management.