A nutrient budget for the Meat and Wool Economic Service of a New Zealand Class 1 high-country farm model

Data on the physical and financial performance of farms are collected annually by the Meat and Wool Economic Service of New Zealand. We used the available data from 1968/69 to 1995/96 to calculate a nutrient balance for the model high-country farm. Our nutrient budget takes account of the loss of nutrients in the form of livestock products (meat and wool), and losses or movement due to leaching and rainfall run-off. Inputs of nutrients occur with the application of fertiliser, in rainfall, and by legumes fixing nitrogen. While there have been large fluctuations in both the quantity of nutrients applied as fertiliser and the quantity of nutrients removed, the whole-farm nutrient balance has remained in credit each year for the whole of the time series for all major nutrients. Separate budgets for developed and undeveloped grassland showed that the nutrient balances were in credit for four of the five nutrients in each case; in developed grassland mean potassium balances were slightly negative while in the undeveloped grassland phosphorus balances were slightly negative. The annual surplus of calcium is significantly higher than for other nutrients. The results indicate a need for re-interpretation of nutrient losses calculated for post-European settlement as they affect understanding of the effects of grazing on the sustainability of high-country grasslands. Over the 30 years studied there appears to have been a cessation and probably some redress of nutrient losses from the system. This indicates that losses were greater earlier in the 150-year period of European settlement than are indicated by the long-term averages.