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Published: 20 Aug 2020

Samantha Flight

Honours student Samantha Flight has identified a new and potentially more profitable way for Tasmanian dairy farmers to manage their pastures.

TIA Dairy Extension Officer, Samantha Flight, undertook an honours project to find out if milk urea nitrogen (MUN) - based on the concentration of urea in milk - could be used by Tasmanian dairy farmers as a useful additional tool for helping to decide when and how much nitrogen fertiliser to apply to their pastures.

“The Tasmanian dairy industry is largely a pasture-based system, and this provides farmers with a competitive advantage as grazed pasture is relatively low-cost. But to maintain this competitive advantage, farmers need to be feeding cows well and managing pastures well,” Ms Flight said.

“Protein and energy are key nutritional elements in a milking cows’ diet and are essential to achieving milk production potential. The application of nitrogen fertiliser is used to drive pasture growth, however it is difficult to analyse the quality of pasture in a timely manner to check if the amount applied was correct.

“There is an opportunity to use MUN to determine the effectiveness of fertiliser usage on dairy farms. We can look at MUN to determine whether protein levels in pastures and resultingly the cow diet are too high or too low at various times during the season and farmers can adjust their management decisions accordingly. For example, if protein in a cow’s diet is low then MUN is also expected to be low.”

Ms Flight said MUN was commonly used by farmers in the Northern Hemisphere as an indicator of the efficiency of protein in the diet of dairy cows but was not a tool that was currently utilised in Tasmania.

“Based on the findings of my honours project, it appears that if MUN results are received on a regular basis such as from bulk tank milk samples, it can provide farmers with a useful indication of when pastures are low in nitrogen or when nitrogen levels are too high and fertiliser is being wasted,” Ms Flight said.

“This has real potential to provide productivity and profitability benefits and also environmental benefits through avoiding excess nitrogen negatively impacting the environment through leaching, run-off and N20 emissions.”

Ms Flight’s project involved analysing 1204 herd tests conducted on 158 Tasmanian dairy farms over three years and surveys with 24 farmers looking at cow diet and fertiliser usage.

Ms Flight said she would like to see extension tools developed to facilitate the sharing of this information to Tasmanian dairy farmers such as an easy to use decision making tree outlining thresholds of MUN and management at each of these levels.

“It would be great if we could start using MUN as a management tool as already happens in the Northern Hemisphere,” she said.

TIA is a joint venture between the University of Tasmania and the Tasmanian Government.