Potassium and Phosphorus Fertilization of Grass Pastures

IPNI-2012-USA-FL31

25 Mar 2015

2014 Annual Interpretive Summary


Pasture fertilization plays a vital role in the success of modern forage-based livestock production systems. Despite the University of Florida recommendations for K and P fertilization of highly-productive hayfields and pastures, many forage producers do not supply adequate amounts of K and P to replace the nutrients exported in harvested forage. The relatively large K removal associated with the sandy-textured soils and it's associated low K-buffering capacity can lead to severe K deficiency symptoms, particularly in mechanically harvested forage production systems. The objective of this study was to evaluate Jiggs bermudagrass (Cynondon dactylon (L.) Pers.) and limpograss (Hemarthria altissima Stapf. and Hubbard) responses to K and P fertilization. The study was conducted at the University of Florida, Range Cattle Research and Education Center, Ona, Florida. Treatments consisted of minimum fertilization regimens that could maintain optimum forage yield, nutritive value, and stand persistence. Because limpograss is often conserved as a stockpile grass, this study also investigated the effect of harvest frequency (four harvests compared with two harvests per year) on limpograss responses to K and P fertilization. Potassium and P were applied in 2012, 2013 and 2014 at application rates of 0, 40, and 80 lb K2O/A, and 0, 20, and 40 lb P2O5/A per year, respectively.

Cumulative Jiggs dry matter yield (DMY) in 2014 increased linearly (~ 3.5 to 4.8-fold) as K application increased. Similarly, K fertilization increased limpograss DMY by as much as 47% relative to the control treatments (8,790 vs. 12,900 lb DM/A for treatments receiving 0 and 80 lb K2O/A, respectively). Despite the positive effect of K, Jiggs and limpograss DMY observed in 2014 were significantly lower than those obtained in the first year of study. Although the amounts of K exported via aboveground biomass were, in general, similar or less than those applied as fertilizer, K fertilization at the levels tested in this study was not sufficient to sustain the same level of production during the 3-yr study. Data also indicated that considerable stand losses and concomitant weed infestation occurred at the end of the study. Similar to the previous years, no effect of P on Jiggs and limpograss DMY was observed. Similarly, K and P fertilization showed no effect on soil chemical properties. Our data indicated that continuous above-ground removal without proper K fertilization results in poor forage performance, stand loss, and weed infestation. Adequate K supply is essential to sustain Jiggs and limpograss productivity and long-term persistence.