Agronomic and environmental impacts of phosphorus fertilization of low input bahiagrass systems in Florida

Phosphorus management in low input bahiagrass (Paspalum notatum Flugge) systems represents a major challenge of agronomic and environmental importance. Concerns over agricultural P transport to surface waters have prompted several revisions in the P fertilizer recommendations for bahiagrass in Florida. This study evaluated the effects of revised P fertilizer recommendations on forage dry matter yield (DMY) and nutritive value and the potential impacts on water quality in bahiagrass pastures growing on a Spodosol. Treatments consisted of the factorial combination of three N rates (0, 56, and 112 kg N ha−1) and four P rates (0, 5, 10, and 20 kg P ha−1), replicated three times and applied annually in May of 2007 and 2008. Forage was harvested at 28-d intervals and DMY, tissue P and crude protein concentration, and P uptake were measured. To monitor P leaching potential, suction cup lysimeters were installed at 15-, 30-, 60-, 90-, and 150-cm depths. In 2007, bahiagrass DMY was not affected by P; however, in 2008 there was a linear increase in DMY from 6.9 to 8.2 Mg ha−1 as P rate increased. In both years, tissue P increased linearly from 2.1 to 2.5 g kg−1 as P rates increased from 0 to 20 kg P ha−1. Similarly, P uptake increased from 14 kg P ha−1 for the control to 19 kg P ha−1 for the treatment receiving 20 kg P ha−1. During the 2-year study, P fertilization had no impact on soil Mehlich-1, water-extractable P, and leachate P concentrations. Leachate P concentrations at the 15- and 30-cm depths varied seasonally (from 0.05 to 0.85 mg P l−1), with greater spikes occurring during periods of high water table conditions. Current P fertilization recommendation can increase bahiagrass DMY with no adverse impacts on water quality.