Differences in sheep production between sites within a heterogeneous area

Two stocking rate experiments were performed within an area of 160 ha with (a) weaners (randomised blocks) and (b) breeding ewes (completely randomised design). Using a quadratic economic objective function to combine outputs of wool, lambs, etc., the range of estimates of optimum stocking rates was, for weaners, from 9 to more than 25 per hectare and, for ewes 8 to 20 per hectare. Analyses of variance showed that residual errors were large compared with the effects of stocking rate, management and years. Where attributes of production were relatively accurately measured and sampled, the between site-within stocking rate variance accounted for approximately 75% of the total residual error.Differences in soil depth, aspect, slope, soil moisture and nutrient characteristics are suggested as the fundamental causes of these block differences. However, the few comparisons available did not permit further analysis. Possible benefits to both farm management and experimentation from predicting site potential from these parameters are discussed.