Differential Orthophosphate Leaching in Empire Zoysiagrass and Floratam St. Augustinegrass

Phosphorus (P) fertilization in low P retention soils can result in P leaching to ground water. This study evaluated the effect of P application rate on orthophosphate leaching (OP) and its relationship with plant P uptake. Floratam St. Augustinegrass (SA) (Stenotaphrum secundatum (Walt) Kuntze cultivar Floratam) and Empire Zoysiagrass (EZ) (Zoysia japonica cultivar Empire) were grown in an uncoated sand soil with very low extractable P and low P retention capacity. Phosphorus was applied every 4 weeks at a rate of 0, 0.14, 0.28, 0.56 and 1.12 g m^-2. Each treatment was replicated four times.  Phosphorus uptake, plant dry matter accumulation, and Mehlich I extractable P were determined biweekly during 120 days (May to August, 2008). In addition, large plastic lysimeters were used to collect leachates, and the amount of OP leached was measured weekly. A decrease (p-value < 0.05) in OP leached with increasing P application rate was observed in SA while OP leached in EZ plots increased with greater P application.  Under the conditions of this study, a cumulative P application of 3.75 g P m^-2 and 1.5 g P m^-2 in SA and EZ, respectively, did not result in an increase in OP leached in comparison to the no P application treatment. Phosphorus uptake rate of SA across treatments and sampling dates was higher (p-value < 0.0001) than in EZ. Root biomass in SA and EZ was not different (p-value = 0.920); however, root length density in SA was greater than in EZ (p-value < 0.0005).