Potassium and Phosphorus Fertilization of Grass Pastures

IPNI-2012-USA-FL31

28 Feb 2013

2012 Annual Interpretive Summary


Pasture fertilization plays a vital role in the success of modern forage-based livestock production systems. The University of Florida recommends K and P fertilization of Jiggs and Limpograss hayfields and pastures; however, many forage production systems do not supply adequate K and P to replace that removed as harvested forage. Because these grasses use large quantities of K as compared to P, soil K deficiency often occurs first, particularly in the highly-yielding crops cultivated in sandy soils with low K-buffering capacity. The objective of this study was to evaluate Jiggs bermudagrass and Limpograss responses to K and P fertilization. The study was conducted at the University of Florida, Range Cattle Research and Education Center, Ona, Florida on a typical Spodosol. Treatments consisted of minimum fertilization regimens that can maintain optimum forage yield, nutritive value, and stand persistence. Because Limpograss is often conserved as a stockpile grass, this study will also investigate the effect of harvest frequency (4- vs. 2-times per year) on Limpograss responses to K and P fertilization. Potassium was annually applied at rates of 0, 40 and 80 lb K2O/A and P was applied at rates of 0, 20 and 40 lb P2O5/A.

Jiggs dry matter yield (DMY) increased linearly with K rates. Application of K at the 40 and 80 lb K2O/A rates resulted in approximately 26 and 44% respective increases in cumulative annual DMY relative to the control treatments (no K added). No differences in DMY were observed in the first harvest when K was applied at rates of 40 or 80 lb/A. This response was due to the dry conditions experienced early in the season. However, during the second and third harvest, Jiggs DMY were consistently greater for the highest K rate. No effect of P or K fertilization was observed on Limpograss DM yields; however, harvest frequency affected yields. Limpograss harvested at 12-week intervals resulted in greater DM yields (3,128 t/A) than the 6-week interval (2,147 t/A). This difference corresponds to approximately 46% more biomass by just increasing the harvest interval. Potassium and P fertilization showed no effect on soil chemical properties. FL-31