Effects of fertilizer and stocking rate on pasture and beef production from sown pastures in northern Cape York Peninsula. 1. Botanical and chemical composition of the pastures

Abstract

The seasonal changes in the yield, botanical composition and chemical composition (nitrogen, phosphorus and sulphur) of the pasture plants were measured in a grazing experiment over three years. The 48 treatments were factorial combinations of two different grasses with a common legume mixture, three annual maintenance rates of phosphorus fertilizer, four stocking rates of continuous grazing and two rates of phosphorus fed directly to the cattle. The pastures consisted of Brachiaria decumbens cv. Basilisk or Panicum maximum (common guinea grass) sown with Stylosanthes guyanensis cv. Endeavour and Macroptilium atropurpureum cv. Siratro. Brachiaria decumbens was more persistent than Panicum maximum when heavily stocked at low fertilizer phosphorus rates and in the latter half of each wet season the legume content of the Brachiaria pastures was lower. Of the two grasses, Panicum maximum contained the higher N, P and S contents. In the third year 20 kg ha-1 of phosphorus gave higher yields than 10 kg ha-1 without affecting the chemical or botanical composition of the pastures but 40 kg ha-1 decreased the legume content of the pastures and raised the phosphorus levels in stylo. Pasture yield decreased with increasing stocking rate with only minor effects on the botanical composition of the pastures. However, there was a concomitant increase in pasture quality, particularly in phosphorus content, with increasing stocking rate.