Grazing management parameters in semi-arid tussock high country

Abstract

At Tara Hills High Country Research Station in North Otago the herbage available on 500.1 ha of steep semi-arid high country was measured for one growing season using a capacitance probe instrument. The technique was evaluated for suitability in steep tussock grassland, and the pattern of grazing pressure on three parallel blocks which comprised the study area was determined. The botanical composition of fresh herbage was estimated visually and related to information about the diet of the sheep obtained from a limited series of faecal cuticle analyses. Fifteen land units were mapped according to the following criteria: Contour concavity, aspect, vegetation and landform elements. The effective pastoral area of each land unit was derived by discounting the rock outcrops and correcting for slope. Two permanent 25m transects were located on each land unit. The thirty transects were measured by capacitance probe on twelve occasions from 31st August 1977 to 9th May 1978. Three to six hours were required for two people to sample and traverse a single block. At each transect inter-tussock herbage was cut in random handfuls at ground-level and placed in a cardboard box beneath the probes until the mean value of 25 readings from the line was obtained. The freshweight and dryweight of the samples were recorded. Available dry matter on each block was estimated from the mean land unit values weights for effective area. The results ranged from 200 kg ha⁻¹ to 1300 kg ha⁻¹. The water content of the herbage on the sunny faces and watercourses averages 59% over the growing season; the shady land units, 53% and the cold/crest land units 43%. On the basis of Penman evapotranspiration data, free soil moisture was present on 63 days in the same nine month period.