Think of Nitrogen as a Supplementary Feeding Alternative

Nitrogen (N) fertiliser can boost pasture growth during feed shortages: for instance, in late breaks to the season and with early lambing ewes. To gain the full economic benefits you must use the additional feed produced, and the largest benefits are when pasture feed replaces the need to buy supplementary feed. Using N fertiliser may allow you to defer grazing of pastures on other parts of the farm while you graze the extra feed available in paddocks where Nitrogen fertiliser was applied.

Typical autumn growth rate responses from Nitrogen are between 15-25kg Dry Matter (DM) per kg Nitrogen (N). The cost of Urea is currently around $680/t and at 46% N, equates to $1.48/kg N plus application costs which would make it approximately $1.55/kg N. At the minimum growth response of 15kg DM/kg N this costs 10¢/kg DM. At the higher response rate (when we have the warmer autumn growing conditions with good moisture) this drops to 6¢/kg DM. With the rising costs of brought-in feed along with the other benefits such as allowing deferred grazing on other areas of the farm, Nitrogen is a viable option, particularly at this time of year.

Table 1 shows that at a response rate of 20:1, if urea was $600/t, and utilisation was 100%, brought-in feed needs to be cheaper than $65/t DM to make it a more profitable option than N fertiliser. At $800/t urea – a farmer in this situation needs to source feed for less than $87/t DM to make it a more profitable choice than urea. Note: Include the costs of delivery and spreading in your urea option costs. Include the cartage and wastage costs in your fodder option costs.

Table 1 Variation in the cost of additional pasture consumed at two urea prices – $600 and $800/tonne.

Extra response kg DM/kg NCost $/t DM at $600/t of ureaCost $/t DM at $800/t of urea

It is advisable to defer grazing for at least two weeks after applying nitrogen to allow the pasture to grow and reduce the risk of nitrate toxicity in livestock.

Tips for Applying Nitrogen

  • Nitrogen-fertilised pasture can be cheaper than purchased feeds, if applied under the right conditions and utilised well. Check the break-even price as urea and other feed option prices change.
  • Apply N to grassy pastures when they are actively growing, have adequate soil moisture to sustain growth and can utilise the additional N.
  • Ensure other nutrients or soil constraints will not limit pasture growth
  • Apply N at rates of 20–40kgN/ha per application, no closer than 21–28 days apart.
  • Do not graze pasture for at least 14 days after N application.

Brooke Anderson, Agronomy Solutions