Fertiliser nitrogen for intensively grazed dairy pastures

Page last updated: Wednesday, 22 April 2020 - 9:29am

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The Greener Pastures project was set up to assist the Australian dairy industry meet the two major challenges in managing high performing pasture systems: maintaining profitability while meeting the expectations of a community that is increasingly sensitive to environmental issues. This page discusses the major findings from a study to define pasture use, milk production and profit responses to increasing levels of fertiliser nitrogen.

Nitrogen response farmlets

From mid-2005 to late 2008,a farmlet study was conducted at Vasse Research Centre (VRC) in the south-west of Western Australia (WA) to compare the performance of pasture and dairy cows when annual ryegrass pastures were top-dressed with one of five rates of nitrogen fertiliser (0 to 2kg/ha/day). Each farmlet was a self-contained, independently managed ‘mini-farm’, with its own paddocks and cows. Cows were milked and fed separately. Pasture was rain-fed and predominantly annual ryegrass with some subterranean clover.

Pastures were rotationally grazed, where readiness to graze was determined by the number of ryegrass leaves grown since the last grazing. Grazing occurred between 2 and 3 leaves, depending on the time of year.

Nitrogen fertiliser was applied each time a herd left a paddock after grazing. The amount applied was based on the number of days since the last grazing, multiplied by the nitrogen level for the farmlet (0 to 2kg/ha/day). For example, if it had been 30 days between grazings for a Farmlet 2 paddock, then 15kg/ha nitrogen would be applied (30 days x 0.5kg/ha/day).

The main messages for farmers from this part of the study were:

  • For rain-fed pasture, maximum pasture utilisation in each growing season was achieved by applying 1kg nitrogen/ha/day.
  • Grazing management is critical in making effective use of nitrogen fertiliser. Reducing the time between grazings as pasture growth rates increase following a fertiliser nitrogen application prevents the pasture from fully expressing its growth potential.
  • To ensure maximum use of applied nitrogen fertiliser for pasture production, graze pasture when ryegrass plants have three leaves per tiller.
  • Delaying grazing from two to three leaves can increase utilisation of annual pastures by 20%. This was not achieved in irrigated perennial pastures, most probably due to crown rust infestation over summer.