Visual estimates of available herbage on hill country sheep pastures

Abstract

Available standing herbage over a range of sheep-grazed hill pastures was visually estimated by the same observer at regular intervals throughout the year. The results were compared with dry matter (DM) yield cuts from nine quadrats sited within each paddock. Linear regressions of yield on visual estimates were significant at all times (r²= 0.6-0.9). The analyses showed that the same observer can consistently assess paddock differences throughout the year and between years without using yield cut calibrations. However, the conversion of visual estimates to DM yield values was only possible on occasions in spring and early summer when pastures were green and residual coefficients of variability (RCV) were low. At other times of the year, when RCV values; were high, the observer tended to under-estimate total DM over whole paddocks by over-estimating the green fraction and under-estimating the dead material and had difficulty in maintaining consistency with between-paddock assessments of paddocks of widely differing sward densities. Scoring a number of small plots within each paddock is preferable to whole-paddock estimation methods.