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

Information is lacking on fertilizer requirements for warm-season pasture grasses in Florida. Three strips each of 'Pensacola' bahiagrass (Paspalum notatum Flugge),'Florona' (or 'Ona' in Manatee County) stargrass (Cynodon nlemfuensis 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 (REC), Hardee County, and on one pasture each in Pasco and Manatee Counties. Sections (15.2 by 15.2 m or 50' by 50') of each grass strip were randomly split 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-nutrients mix (NPKM); and 4) control (no fertilizer) as subplots. Fertilizer was applied between March and May 1998 and March 1999 (same plots each year). Forage regrowth in metal exclosures was harvested at 35-d intervals through November for yield and sampled in spring, summer, and fall for crude protein (CP), in vitro organic matter disappearance (IVOMD), and tissue mineral concentrations each year. Forage yield was not affected by fertilizer application at any site except for Pasco in 1998, but yield from the non-fertilized treatment was always lower (8-30%) than fertilized counterparts. In 1999, yields of Florona on pasture 87 and of Floralta in Pasco County were increased with the NPKM treatment over the N or the NPK treatments. Pensacola was the most productive grass under grazing at Hardee sites, but Floralta was most productive at Manatee and Pasco sites. Crude protein concentration was always greater on the N-fertilized treatments, but IVOMD was generally unaffected except in Pasco where IVOMD was lower on the non-fertilized control (480 vs. 490 g kg(-1)). Mineral concentrations in grass tissue were not related to grass or fertilizer treatment although they varied throughout the season. These data suggest that the application of P and K to grazed pastures in south Florida could be reduced without a major negative impact on production, but micro-nutrients with NPK may be needed in isolated cases.