RESPONSE OF PENSACOLA BAHIAGRASS TO RATES OF NITROGEN, PHOSPHORUS ANDPOTASSIUM FERTILIZERS

There is little information to suggest the optimum fertilizer treatmen t for Pensacola bahiagrass, Paspalum notatum var. sauri, a warm-season perennial pasture grass that occupies 2.5 million ha in the southeast ern USA. Objectives of this 3-yr study were 1) to establish the N, P, and K requirements of three Pensacola bahiagrass entries planted on a previously uncropped Clarendon loamy sand (Plinthaquic Paleudults), 2) determine which of eight N-P-K fertilizer treatments could best satis fy those needs, and 3) measure the effects of fertilization and treatm ents on Mehlich-1 extractable P and K. Fertilizer interactions reveale d that fertilizer response of all three entries was similar. Rates of 56, 112, 224 and 448 kg N ha(-1) produced average annual dry matter (D M) yields of 6010, 8240, 11900 and 15 200 kg ha(-1). With N applied at 224 kg ha(-1), plots receiving N-P2O5-K2O ratios of 4-1-1, 4-1-2, 4-1 -3 and 4-2-4 did not differ in DM yield (P=0.05). Nitrogen concentrati on in the DM increased from 10.6 to 17.0 g kg(-1) as fertilizer N incr eased from 56 to 448 kg ha(-1). Phosphorus concentration in the DM rem ained at 1.4 or 1.5 g kg(-1) until P2O5 was increased from 56 to 112 k g ha(-1) and then increased to 1.7 or 1.8 g kg(-1). Increasing K2O rat e from 56 to 112 kg ha(-1) increased K concentration in the DM from 14 .8 to 21.1 g kg(-1). Dry matter content in green forage decreased from 354 to 307 g kg(-1) (fresh-weight basis) as N increased from 56 to 44 8 kg ha(-1). Fertilizer rates had no effect on forage IVDMD. Fertiliza tion increased Mehlich-1 extractable soil P in the surface 0.91 m abov e values found in unfertilized plots which were not harvested. The inc rease was significant where either N was limiting production or more t han 56 kg P2O5 ha(-1) was applied each year. Mehlich-1 K in the profil e decreased as production increased due to increased N application, un less more than 100 kg K2O ha(-1) was applied yearly.