Effect of superphosphate application on the phosphorus status of breeding cattle grazing Townsville stylo based pastures in northern Queensland

Abstract

The performance of Brahman crossbred cows grazing annual grass plus Townsville stylo (Stylosanthes humils) pasture with or without superphosphate fertilizer was monitored over a two year period. The animals were introduced to the experimental areas as yearling helfers and remained until weaning of their first calf. Levels of phosphorus In rib bone varied between 145 and 172 mg/ml. At weanlng, levels were higher on the fertilized than on the unfertilized pasture (172 vs. 157 mg/ml). Calcium levels in rib bone varied between 329 and 362 rng/ml and paralleled bone phosphorus levels. Pasture nitrogen levels were similar on both pastures but phosphorus levels were higher on the fertilized area. Faecal analyses reflected this same pattern with faecal nitrogen levels being similar on both pastures, and faecal phosphorus levels higher on the fertilized pasture. Liveweight changes of cows and calf weaning weights were greater in groups grazing the fertilized pasture. It is hypothesized that this superior performance is a function of increased feed intake resulting from increased phosphorus intake on the fertilized area although the possible contribution of sulfur cannot be overlooked.