Phosphorus Mass Balance for Bahiagrass Pastures Growing on a Typical Florida Spodosol as Affected by Phosphorus In the Spodic Layer.

We evaluated the role of the spodic (Bh) horizon on the overall P mass balance in a typical bahiagrass (Paspalum notatum Flugge) pasture grown on a Florida Spodosol. Treatments consisted of three P rates (0, 5, and 10 kg ha^-1) arranged in a completely randomized design with each plot receiving a basal application of N at 56 kg ha^-1 and K at 47 kg ha^-1. Application of P had no effect on bahiagrass P uptake during the 2-yr study (P = 0.2). Average P mass leached below the 45-cm soil depth was 0.08 kg P ha^-1 for the zero P control, 0.08 kg ha^-1 for the 5 kg P ha^-1 treatment, and 0.09 kg P ha^-1 for treatment receiving 10 kg P ha^-1. In 2007, the net balance of P in the Ap horizon was -10.8 kg P ha^-1 for the control, and -0.8 kg P ha^-1 for the 10 kg P ha^-1 treatments. The same treatments had net P balance of -6.6 and 7.2 kg ha^-1 in 2008. When soil P held in Bh horizon was included in the P mass balance computation, net P balance was positive for all treatments including the control, which indicates that soil P concentrations were sufficient to maintain bahiagrass production and no P fertilization would be required. Results suggested that P held in the Bh horizon is a significant supply of P to low input pastures growing on Spodosols in Florida and should be considered in nutrient management programs for perennial grasses.