Is nitrogen fertiliser an economic option in tussock hill country?

Abstract

Abstract Tussock hill and high country is a finite resource. Farmers are developing these areas to increase production but often at the expense of tussock which provides shelter for stock, increases biodiversity and captures moisture in dry environments. An experiment at a single hill country site near Roxburgh, Otago was established on oversown tussock with soil of low pH (5.1) and high soluble aluminium (15 ppm) to compare the use of capital lime (0-5 t/ha), annual and capital superphosphate (0-1000 kg/ha) and annual nitrogen (N) fertiliser inputs (0-150 kg/ha) over 4 years to investigate the potential of different fertiliser strategies to increase economic returns. Annual yield of the Control without fertiliser was approximately 3200 kg DM/ha/annum, which may support an estimated stocking rate of 6 ewes/ha during the growing season. Using lime did not increase the pasture production or stocking rate, though even small amounts increased pasture quality. Use of phosphate and sulphur increased the stocking rate to approximately 9 ewes/ha, while adding N fertiliser increased potential stocking rate to approximately 12 ewes/ha. These increases were a combination of increased pasture production and increased pasture quality. A combination of phosphate, sulphur, lime and nitrogen provided a potential net increase in gross margin of $200/ha. This cost benefit analysis suggests that regular use of N fertiliser along with other known fertiliser requirements may be a very cost effective way of increasing hill country production without resorting to full scale tussock development. Keywords: gross margin, hill country, fertiliser, quality, sheep stocking rate, yield.