title: Timing of phosphorus fertilizer application within an irrigation cycle for perennial pasture.
abstract: Irrigated pastures are significant contributors of phosphorus (P) to inland watercourses, with much of the P coming from applied fertilizer. It was hypothesized that the timing of P fertilizer application relative to irrigation regulates P concentrations in runoff and infiltrating water. To test this hypothesis, a two-by-two factorial experiment was conducted on twelve 8- x 30-m border-irrigated bays growing perennial pasture. Phosphorus fertilizer in the form of single superphosphate (44 kg P ha(-1)) was surface-broadcast onto the bays when the nominal change in soil water deficit reached 0 or 50 mm (U.S. Class A pan evaporation minus rainfall). Following fertilizer application, the bays were again irrigated when the nominal soil water deficit between fertilizing and the subsequent irrigation reached either 0 or 50 mm. The volume of water applied, runoff volume, and changes in soil water content were recorded for the three irrigations following fertilizer application. Total phosphorus (TP) and filtrable reactive phosphorus (FRP, <0.45 microm) concentrations in runoff and at depths of 0.1, 0.3, and 0.6 m in the soil were also measured. Soil water content at fertilizer application had less effect on P concentrations in runoff and soil water than the additional time between fertilizing and irrigating. By allowing a deficit of 50 mm between fertilizer application and irrigation, the average concentration of P in runoff and moving below a soil depth of 0.1 m was approximately halved. To maximize fertilizer use efficiency and minimize environmental effects, a delay should occur between applying P fertilizer and irrigating perennial pasture.
authors.affiliation: Dep of Natural Resources and Environment, Institute of Sustainable Irrigated Agriculture, Tatura, Victoria, Australia. garnc@bigpond.com
authors.forename: B J
authors.initials: BJ
authors.lastname: Bush
authors.forename: N R
authors.initials: NR
authors.lastname: Austin
mesh_terms: D000383:Agriculture / Q000379:methods; D005308:Fertilizers; D010758:Phosphorus / Q000032:analysis*; D013997:Time Factors; D014872:Water Movements; D014873:Water Pollutants / Q000032:analysis*; D014876:Water Pollution / Q000517:prevention & control
chemical_list: D005308:Fertilizers; D014873:Water Pollutants; D010758:Phosphorus