Nitrogen can be a cost-effective way to grow extra feed this spring and beat high bought-in feed prices, providing soil moisture is right.
University of Melbourne nitrogen expert, Professor Richard Eckard said ryegrass growth was strong in warmer temperatures at 18-21 degrees Celsius.
A typical response to nitrogen in those conditions is 10 kilograms of dry matter for every 1kg of N.
"That's a typical response and if the soil moisture is there you can get responses 15kg-18kg DM to 1kg N as temperatures increase," Mr Eckard said
Gippsland-based consultant Matt Harms said nitrogen boosted pasture could be significantly cheaper than imported fodder right now.
"With urea at $600/tonne and then nitrogen at $1300/tonne, if we can grow and harvest all that response that means the cost is around $130/tonne DM," he said.
"That's pretty valuable fodder going down the throat of cows when you look at grain concentrates at $500/tonne."
Mr Eckard said applying nitrogen could be useful until the end of October. "If the prediction is for a drier, late spring, you'd keep going as long as soil moisture was there, and as long as the grain price is high and other feed sources are high it's cost-effective," he said.
How much does nitrogen grown grass cost? This will depend on the cost of urea, the response rate and the utilisation (how much of the extra growth is used). Table 1 shows, even at below average response rates e.g. 10:1, additional pasture grown compares favourably with current costs for purchased feeds (particularly purchased hay and silage).
When purchased feed prices are high, below average response rates will be profitable.
Pasture conservation In the case of pasture conservation, it is recommended to apply N at a higher rate (up to 60kg of N/ha in later spring), after grazing when the pasture is closed up for conservation.
Results from using split applications of N, for example after grazing and again partway through regrowth, are more variable, and this practice isn't recommended.
What influences the response rate to nitrogen?
The amount of pasture grown in kg DM/kg N applied is the 'response rate'. For example, where 30kg N/ha is applied and an additional 300kg DM/ha of pasture is grown, the response rate is 10kg DM/kg N fertiliser applied.
The response rate is dependent on: Amount of available N in the soil - the greater the deficit, the higher the response. Soil temperature - the warmer the soil, the greater and more immediate the response. Plant growth - the higher the growth rate potential, the greater and more immediate the response. Also better species composition means better responses. Moisture - too much or too little water will lower the response. The best response is from a full profile. Rate of N applied per application - there is a diminishing response at high application rates, but also an unreliable response at low rates, therefore stick to rates between 20 and 50kg N/ha per application depending on the additional growth required. The availability of other plant nutrients and soil pH.
General guidelines for N management Apply N strategically, rather than by fixed recipe: Before each N application estimate the likely N response (i.e. from look-up tables, experience, and farm consultants) and compare the cost of additional pasture produced to other purchased feed options. Only apply N when the pasture is actively growing and can utilise the N. Ensure soil moisture is adequate to sustain the regrowth and temperatures are conducive to good pasture growth. Apply N at rates of 20-50 kg N/ha per application, no closer than 21 to 28 days apart. Ensure that the extra pasture grown is utilised either through grazing or as harvested forage, as utilisation has a big impact on the economics of using N. To get the most out of N application on ryegrass, graze as close to 2.5 leaves to canopy closure as possible. Do not graze perennial pastures for 7 to 14 days after nitrogen application, as this is when nitrate levels are highest. Other forage types and weedy paddocks may need to be left longer. Cloudy or overcast days will increase the time needed before paddocks can be grazed after nitrogen application.D
Learn more at website www.dairyaustralia.com.au/feedshortage.