Soil changes associated with cessation of sheep grazing in the Canterbury high country, New Zealand

Soil characteristics were examined within and adjacent to two vegetation exclosures near Porters Pass, Canterbury retired from grazing 45 years ago. Soils were analysed for a range of simple physical (topsoil depth, bulk density), chemical (pH, exchangeable cations, P, S, total C and N) and biochemical (microbial carbon) properties to determine whether the vegetation recovery inside the exclosures was reflected in soil differences. At both sites there were few significant differences between the exclosure and the surrounding grazed area, despite vegetation recovery since exclusion of grazing. At Starvation Gully topsoil depth 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 the 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 matter in the exclosure at Starvation Gully, and the reverse at Cloudy Knell. 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 change of soil properties following cessation of grazing and the need to sample soils, litter and vegetation when determining trends in organic matter and chemical fertility.