SOIL CHANGES ASSOCIATED WITH CESSATION OF SHEEP GRAZING IN THE CANTERBURY HIGH COUNTRY, NEW-ZEALAND

Soil characteristics were examined within and adjacent to two vegetati on exclosures near Porters Pass, Canterbury retired from grazing 45 ye ars ago. Soils were analysed for a range of simple physical (topsoil d epth, bulk density), chemical (pH, exchangeable cations, P, S, total C and N) and biochemical (microbial carbon) properties to determine whe ther the vegetation recovery inside the exclosures was reflected in so il differences. At both sites there were few significant differences b etween the exclosure and the surrounding grazed area, despite vegetati on recovery since exclusion of grazing. At Starvation Gully topsoil de pth and Na were higher, and bulk density, pH, K, total C, total N and microbial C mass, and the microbial C to total C ratio were lower in t he exclosure. At Cloudy Knell Ca, Mg, total C and N were higher and Na was lower in the exclosure. There was a marked contrast in the trends at the two sites, with slightly lower nutrient status and organic mat ter in the exclosure at Starvation Gully, and the reverse at Cloudy Kn ell. The differences between the sites probably reflect differences in the partitioning of nutrients and organic matter between vegetation, litter and soil at the two sites. The results suggest a slow rate of c hange of soil properties following cessation of grazing and the need t o sample soils, litter and vegetation when determining trends in organ ic matter and chemical fertility.