The profitability of nitrogen fertiliser usage on Canterbury irrigated sheep farms

Abstract

The profitability of nitrogen usage on Canterbury irrigated sheep farms was investigated using a deterministic feed budget model. Effects of nitrogen usage on stocking rate and animal performance was determined. Current prices were used to determine profitability using partial budget analysis. Pasture nitrogen responses were thoroughly researched, and used as parameters in the model. Spring applied nitrogen with good (20 kgDM/kgN spring), medium (13.4 kgDM/kgN) and poor (6.2 kgDM/kgN) responses were used. Autumn responses were assumed to be 80% of spring responses. The application of 40 kgN/ha in spring and autumn increased carrying capacity by approximately 9, 6 and 3% when good, medium and poor responses respectively were realised. Despite 20% lower nitrogen responses in autumn, there was little difference in carrying capacity between spring and autumn applied nitrogen. Autumn applied nitrogen reduced the supplementation requirement. The extent of this depended on response efficiency and application rate, and was most apparent when lambing rate was increased to 140%. Spring applied nitrogen responses generally occurred too late to reduce the supplementation requirement. The increase in feed requirements which occurred when lambing rate increased from 120 to 140% could have been met by the application of 10 kgN/ha associated with a medium nitrogen response of 13.4 kgDM/ha. The use of nitrogen to increase lambing rate was discussed. Financial analysis identified nitrogen response, lambing percentage, supplementation requirements, and price ratios as the most important factors determining profitability. Profitability increased with lambing percentage. Autumn applications were more profitable than spring applied nitrogen. At current prices, only autumn applied nitrogen for ewes with a lambing rate exceeding 127% was found to be profitable at average autumn responses of 10.7 kgDM/ha. It was concluded that profitability of nitrogen usage is marginal. Nitrogen usage and factors determining profitability were discussed.