Is nitrogen fertiliser an economic option in tussock hill country?

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.

Soil aluminium toxicity in New Zealand pastoral farming – a review

“…On a previously oversown tussock grassland upland site in Central Otago dominated by browntop, Yorkshire fog, crested dogstail and sweet vernal with a small white clover component, Stevens et al (2014) could not measure a significant (P>0.05) pasture production response to lime over 4 years at a high soil CaCl 2extractable Al level of 17.5 ppm and low soil pH of 5.1, with a mean annual rainfall of 560 mm. This lack of response to lime could be attributed to the relative tolerance of these unimproved grass species to soil Al toxicity and reinforces the necessity of having sufficient legume to justify the cost of lime application.…”

What are the best pasture improvement options for different South Island hill and high-country environments?

“…On three sites with rainfall of 450 to 575 mm/yr where grasses were sown (Scott and Maunsell 1981, Pollock 1989, Stevens et al, 2014, Fasi 2018, there was an average pasture yield of 5090 kg DM/ha/yr (range 3000 to 7000 kg DM/ha/yr) but a negative partial GM of -$47/ha/yr (range -$234 to $227/ha/yr). This poor financial return was mainly caused by the excessively high cost of the 345 kg N/ha/yr applied at one site and the unnecessary application of 5 t lime/ha/yr where the initial soil pH was 5.5 at another site.…”

The effects of lime on pasture composition and production in western Waikato hill country

“…Thus, any amelioration by lime might be expected to lead to a long-term shift in botanical composition in mixed swards. However, Al-tolerant pasture species have shown no significant responses to lime at low pH (5.1) and high Al levels (17.5 CaCl 2 -extractable, Stevens et al 2014). This trial was instigated by a group of local Waikato hill country farmers who had observed marked changes in their pastures and stock grazing preferences following lime applications and were keen to obtain data and insight into why this was so apparent.…”