PHOSPHORUS MOVEMENT IN THE LANDSCAPE

Phosphorus movement in runoff often promotes algal growth in lakes. Thus, agricultural soils and management practices that enhance the potential for P movement must be identified. The main factors controlling P movement are transport (runoff and erosion potential) and source factors (surface soil P and method, rate, and timing of fertilizer and animal manure applications). Implementation of management that minimizes runoff and erosion will reduce P transport in runoff, although total algal availability can increase. The continued application of P has increased surface soil test P contents in excess of levels sufficient for optimum crop yields. Although increases in soil P have been related to P enrichment of runoff in plot and watershed studies, information for given management systems still is needed to reliably quantify critical soil B levels above which excessive P enrichment of runoff will occur. Clearly, P applications must be carefully managed, in addition to minimizing transport potential, to efficiently reduce P movement in landscapes. This may be achieved with regular soil testing, P incorporation, application during times of low runoff probability, and irrigation management.