Effect of soil slip erosion on seasonally dry Wairarapa hill pastures

Abstract

Production, botanical composition, and some soil fertility parameters of pastures on seasonally dry Wairarapa hill country subject to soil slip erosion were measured over 3 years, beginning in 1979. Measurement sites were on sunny and shady aspects of ‘uneroded’ areas of hillslopes, and slip scars of 4 ages (mean dates of slipping: 1977, 1961, 1941, and 1906). Average annual pasture production on uneroded areas was 8391 kg DM/ha. Pasture yields on the 1961, 1941, and 1906 sites, and the 1977 sites were about 77 and 20% of this level respectively. Uneroded sites were generally less steep than eroded sites, and this complicated interpretation of data. Correction for this slope discrepancy would increase the 77 and 20% values slightly. The results of this study suggested that pasture production on hill soils formed under pastoral agriculture was unlikely to return to the production levels supported by soils formed under the original forest vegetation. Botanical composition of pastures was influenced by the time elapsed since erosion. Grass dominance increased, and legume dominance decreased, with increasing length of time since slipping. Uneroded sites were the most grass dominant. N and C contents of soil increased with time since slipping, but were much lower for soils on all slip scars than soils on uneroded sites.