Trial aims to avoid costly losses of nitrogen fertiliser

Graham Mussell (in hole) installing a lysimeter to capture leached soil water at the nitrogen trial site near Busselton.

Nothing frustrates beef and sheep producers like a late break-of-season. After months of supplementary feeding, the rain comes when temperatures are cold, slowing the break-down of organic soil nitrogen and pasture growth, and creating less than ideal conditions for grazing.

In this situation nitrogen fertilisers are often used to boost winter pasture growth. However, evidence suggests that significant amounts can be lost through leaching, resulting in poor pasture response and ending up in waterways where it can cause serious water quality issues. So how can farmers reap the benefits associated with nitrogen fertilisers while avoiding an environmental cost?

In South West Western Australia, a new trial has commenced in the Vasse-Wonnerup Catchment to help beef and sheep producers better manage nitrogen fertiliser. Led by agronomist Graham Mussell and livestock specialist Jeisane Accioly, the trial will focus on maximising nitrogen use efficiency in livestock production systems.

“The trial aims to gain a better understanding of how nitrogen loss varies with rate, application timing and the type of nitrogen fertiliser on a typical sandy loam on coastal plains,” Mr Mussell said.

“Water is a key driver of nitrogen loss, with big rainfall events causing nitrate to move below the root-zone, particularly when plants are growing slowly in winter. The trial will show this seasonal loss by capturing soil water with lysimeters, which have been buried beneath each plot, and analysing leachate nitrogen content.”

To minimise loss while maintaining production, recommendations have been made to apply less nitrogen (25-50 kg/ha N) more often (no closer than 21-28 days apart). However, this recommendation can be impractical for beef and sheep producers who sometimes lack the time and equipment to apply nitrogen regularly or can’t access paddocks at certain times of the year. An alternative being tested in the trial is to use enhanced efficiency fertilisers that use coatings to delay nitrogen release, or inhibitors that slow the conversion of ammonium to nitrate which is more easily leached.

Livestock specialist Jeisane Accioly, who is also the Executive Officer for Western Beef Association Inc, hopes that these products will boost production and minimise environmental impacts in other ways.

“A steadier supply of fertiliser nitrogen will also help to decrease “spikes” in the plant nitrogen content,” Ms Accioly said. “These spikes can affect animal nutrition and production, and because ruminants are not efficient users of nitrogen, any oversupply is excreted, increasing the environmental load.”

The project is supported by the South West Catchments Council, through funding from the Australian Government’s National Landcare Program, and by Western Beef Association Inc. To keep up to date, follow the social media hashtag #NRightTrial.

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