Interrelationships of stocking rate and superphosphate rate on pasture as determinants of animal production. I. Continuously grazed old pasture land

Abstract

Merino wethers were grazed continuously on a predominantly annual pasture in the Mediterranean environment of South Australia to assess the animal and pasture responses to, and financial returns from, factorial combinations of stocking rate and superphosphate. Stocking rate and superphosphate both significantly influenced pasture production, pasture availability, percentage pasture utilization and consequent sheep body weight, wool production, and wool value. Neither main effect markedly influenced botanical composition. Significant interactions between stocking rate and superphosphate occurred in relation to sheep body weight on some occasions during the third year of the experiment, and in the case of wool per head, wool per acre, and value of wool per acre in the second and third years of the experiment. The results showed clearly that there was no economic justification for applying high levels of superphosphate to old pasture land unless the additional pasture production was utilized through an increased stocking rate. Only at the high stocking rate was there a significant correlation between pasture production and wool production. At this high stocking rate there was marked dependence on medium or high rates of application of superphosphate to ensure satisfactory levels of pasture production, pasture availability, wool production, sheep survival, and profitability.