PASTURE RESPONSES TO GRAZING MANAGEMENT IN HILL COUNTRY

Abstract

Components of growth and defoliation of perennial ryagrass and browntop tillers and white clover stolen apices ware measured for 12 months in hill pastures set stocked (SS) or rotationally grazed (RG) with sheep. Leaf appearance intervals of the grasses were unaffected by grazing management. Tiller densities were greater under SS (annual mean 29,700 total tillers/m' cf. 20,100/m* under FIG), compensating for greater leaf extension rates and lamina lengths of individual tillers under RG. White clover leaf appearance intervals were similar under both managements except in summer when RG was superior to SS during 3 grazing rotations. Defoliation of grass tillers was more frequent under SS when rotation lengths exceeded 3 weeks, but more severe (in terms of leaf length removed) under RG throughout the year. These mechanisms, combined with tiller density differences.contributed to the likelihood of equal leaf removal per unit area under both managements. Some advantage to RG in ryegrass leaf growth and total leaf removal was indicated but the differences were small and unlikely to affect animal production. White clover leaf removal was similar under both managements. Grazed swards are dynamic and can change rapidly under different grazing managements; however, at acceptable levels of pasture utilisation, the dominant responSes appear to maintain an equilibrium in leaf growth. Thus the use of other procedures, e.g. fertiliser application and increases in stocking rate, in conjunction with management changes is required to substantially alter pasture and animal production. Keywords: hill country, grazing management, pasture productivity, perennial ryegrass, browntop, white clover, leaf growth, tiller density, defoliation frequency, defoliation severity.