Min Liu and Jerry Sartain. University of Florida, 414 Newell Hall, PO Box 110510, Gainesville, FL 32611
St. Augustinegrass [Stenotaphrum secondatum (Walt.) Kuntze] is widely used in Florida as a lawn grass. At present phosphorus (P) fertilization of Florida lawn grasses is based on soil tests which were designed for agronomic crops in a production culture. Little information exists relative to the exact P requirement of St. Augustinegrass. The objective of this study was to determine the critical P requirement of St. Augustinegrass grown in a Hyperthermic uncoated typic Quartzipsamments Entisol in a glasshouse. Established pots of ‘Floratam’ were subjected to P treatments of 0, 0.3125, 0.625, 1.25, and 2.5 g P2O5 m-2 per four weeks for 84 days after P deficiency was induced. The P source used was concentrated super phosphorus. Measurements included tissue growth rates, tissue P concentration, visual ratings of turfgrass quality, leachate soluble reactive P concentration and soil Melich-1 P concentration. Phosphorus treatments increased tissue P concentration with each successively higher P application. The highest P application resulted in the greatest quantity of leaching loss P of 6.3 mg, which accounted for 0.8% of total P applied. The critical soil Melich-1 P concentration corresponding to the critical tissue P concentration (1.4 g kg-1) was 3.9 mg kg-1. The P application rate corresponding to the critical soil P concentrations was approximately 0.3125 g P2O5 m-2 per four weeks. The critical tissue P concentration, soil test P concentration and the minimum P application rate can be used as references to determine the minimum fertilization level of St. Augustinegrass in the routine soil testing program for sandy soils.
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