Phosphorus Fertilization Responses on Bahiagrass Pastures: Forage Production and Water Quality

Abstract

The increased cost of fertilizer and concerns about environmental impacts have led to a reduction in P use in grazed pastures in Florida; however, P fertilization may be necessary to sustain bahiagrass (Paspalum notatum Flügge) pastures. This study evaluated the impacts of reduced P fertilization on forage characteristics, soil and leachate P concentrations on bahiagrass pastures during 2007 and 2008. Treatments consisted of three P fertilization levels (0, 5, and 10 kg P ha−1, applied as KH2PO4) arranged in a randomized complete block design with four replicates. Twelve 1.2‐ha bahiagrass pastures were stocked continuously with a fixed stocking rate of two beef heifers [Bos sp; 380 ± 30 kg live weight (LW)] per experimental unit. Forage was sampled at 14‐d intervals for herbage mass (HM), crude protein (CP), and in vitro digestible organic matter (IVDOM) concentrations. Two suction lysimeters were installed at 60‐ and 90‐cm depth to monitor leachate P. Phosphorus fertilization did not affect HM (4.4 Mg ha−1), herbage accumulation rate (HAR, 43 kg ha−1 d−1), CP (94 g kg−1), or IVDOM (500 g kg−1). Tissue P concentrations increased from 1.9 to 2.2 g kg−1 as P fertilization increased from 0 to 10 kg P ha−1 Soil P concentration in the Ap (7 mg kg−1) and Bh horizons (23 mg kg−1) and leachate P concentration (0.06 mg L−1) were not affected by P application. Despite the lack of yield response to P fertilization, P application at levels of 5 and 10 kg P ha−1 showed no impacts on water quality.