Effect of P and K fertilizer on forage yield and nutritive value of floralta limpograss

Improved perennial grasses have shown little yield response to P and K fertilization on flatwoods soils under grazing conditions. Ten treatments consisting of four with P (0, 10, 20, 40 kg P ha(-1) with N and K constant at 67 and 74 kg ha(-1) respectively); four with K (0, 37, 74, 148 kg K ha(-1) with N and P constant at 67 and 20 kg ha(-1), respectively); 67-20-74 kg N-P-K ha(-1) plus micro-nutrients mix; and a control (no N, P, K) were applied to 1.5 by 6.1 m centers of 3.0 by 6.1m plots of a 'Floralta' limpograss (Hemarthria altissima [Poir] Stapf and C. E. Hubb) pasture that had not been fertilized with any P or K for the previous 9 yr to evaluate the effects of P and K fertilizer rates on a limpograss pasture that had a prolonged history of no P and K fertilization. The pasture was on a transitional flatwoods soil on a pond margin and was used mainly for September to March grazing each year. Following cattle removal, soil was sampled, forage residue removed, and fertilizer treatments applied to plots in four randomized complete blocks on 12 June 1998. Forage was harvested at 35-d regrowth, plots were immediately cleaned off and a second fertilizer treatment application was made to the same plots. A second forage harvest was taken at another 35-d regrowth. The experiment was repeated on the same plots beginning on 14 June 1999. Forage yield showed a positive linear and quadratic response to P in 1998 and linear and quadratic response to both P and K in 1999. Conversely, there were linear or linear and quadratic declines in forage crude protein concentration to P and K depending on harvest date. The application of P or K fertilizer increased tissue concentrations of the respective nutrient applied, but each antagonized the uptake of the other on some harvest dates. Phosphorus increased forage uptake of Mg and Mn but depressed Fe uptake. Potassium decreased Ca and Mg forage uptake. These results indicate that Floralta limpograss forage yield and nutritive value will respond to P and K application on a transitional flatwoods soil if it has not been fertilized for many years.