Biophysical indicators of sustainability of North Island hill pasture systems.

摘要

Four 7-ha farmlets at AgResearch's Hill country Research Station were subdivided into 36 paddocks which differed in aspect, slope and historical management (1973-93). During 1975-80, 2 farmlets had high fertilizer rates and 2 had low rates. One eachof these 4 had fertilizer application discontinued after 1980 (LN and HN), and annual applications of 125 (LL) and 375 (HH) kg superphosphate/ha were continued for the other 2. The paddocks were set stocked with ewes, with stocking rates adjusted to grass production. Nineteen vegetative, soil and water variables were selected as useful biophysical indicators. Analysis of the results for these variables suggested that most of the variance of the data matrix was in response to pasture botanical composition (especially the content of high-fertility responsive grasses and of herbaceous weed species) and earthworm mass/unit area. Management treatment influenced herbage production, soil Olsen P, soil mineral N, exchangeable Ca:Mg ratio, legume production, Nfixation, earthworm mass and grass content, values for these variables being highest for HH and lowest for LN. The pattern for other species content and root surface area was the opposite to this pattern. Soil total S and soil organic matter was highestfor HH and soil water conductivity was greater on L than H treatments. Sustainability as a concept is reviewed and discussed in relation to these results.