Sheep production on a Danthonia caespitosa-Stipa variabilis grassland in response to fertilizers and deferred grazing

Abstract

The effects of nitrogen and phosphate fertilizers and deferred spring grazing were assessed over five years on the body weight and wool production of Merino wether weaners grazing a Danthonia caespitosa-Stipa variabilis grassland at three stocking rates. Seasonal forage availability, botanical composition of forage, body weight and wool growth of sheep, were measured. Two years after grazing treatments ceased, and three years after the final addition of fertilizer, further measurements were made on the vegetation. There were very few differences in plant and animal response between the continuously and deferred grazing systems. Forage availability increased on fertilized grassland at all stocking rates by up to 50 per cent. Danthonia caespitosa, Stipa variabilis, perennial chenopods, and annual herbs contributed to the increase in forage present. Medicago polymorpha became prominent on all fertilized grassland. At 2.0 and 2.7 sheep ha-' without fertilizer, and 2.7 sheep ha-1 with fertilizer, the relative contribution by the more palatable species decreased and Eriochlamys behrii increased greatly. After grazing treatments ceased, this trend was reversed. Sheep body weight and wool growth rates were increased on fertilized grassland. In September 1971, at 2.0 sheep ha-1, the body weights of sheep on unfertilized and fertilized grassland were 35.0 and 45.2 kg, respectively, and the clean fleece weights were 3.2 and 4.3 kg per sheep, respectively. Animal production from this grassland can be increased with the addition of fertilizer to the grassland and by increasing the stocking rate by about 50 per cent above the district average of 1.2 sheep per hectare.