Fertilizer treatment effects on forage yield and quality of tropical pasture grasses

Information is lacking on fertilizer requirements for warm-season pasture g rasses in Florida. Three strips each of 'Pensacola' bahiagrass (Paspalum no tatum Flugge),'Florona' (or 'Ona' in Manatee County) stargrass (Cynodon nle mfuensis Vanderyst) and 'Floralta' limpograss [Hemarthria altissima (Poir.) Stapf & C. E. Hubb] were established in a randomized complete block design on two pastures (71A and 87) at the Range Cattle Res. and Educ. Center (RE C), Hardee County, and on one pasture each in Pasco and Manatee Counties. S ections (15.2 by 15.2 m or 50' by 50') of each grass strip were randomly sp lit into four fertilizer treatments: 1) 67 kg N ha(-1) (60 Ib N/A) (N); 2) 67-12-56 kg NP-K ha(-1) (60-25-60 Ib N-P2O5-K2O/A) (NPK); 3) 67-12-56 kg N- P-K ha(-1) (60-25-60 Ib N-P2O5-K2O/A) plus 22 kg ha(-1) (20 Ib/A) micro-nut rients mix (NPKM); and 4) control (no fertilizer) as subplots. Fertilizer w as applied between March and May 1998 and March 1999 (same plots each year) . Forage regrowth in metal exclosures was harvested at 35-d intervals throu gh November for yield and sampled in spring, summer, and fall for crude pro tein (CP), in vitro organic matter disappearance (IVOMD), and tissue minera l concentrations each year. Forage yield was not affected by fertilizer app lication at any site except for Pasco in 1998, but yield from the non-ferti lized treatment was always lower (8-30%) than fertilized counterparts. In 1 999, yields of Florona on pasture 87 and of Floralta in Pasco County were i ncreased with the NPKM treatment over the N or the NPK treatments. Pensacol a was the most productive grass under grazing at Hardee sites, but Floralta was most productive at Manatee and Pasco sites. Crude protein concentratio n was always greater on the N-fertilized treatments, but IVOMD was generall y unaffected except in Pasco where IVOMD was lower on the non-fertilized co ntrol (480 vs. 490 g kg(-1)). Mineral concentrations in grass tissue were n ot related to grass or fertilizer treatment although they varied throughout the season. These data suggest that the application of P and K to grazed p astures in south Florida could be reduced without a major negative impact o n production, but micro-nutrients with NPK may be needed in isolated cases.