Pasture production potential may be underestimated as temperatures drop this winter in southern areas where the autumn break was exceptional.
Warmer winters, and the implications that has for plant growth and nitrogen, was the topic of discussion at the latest Meat & Livestock Australia productivity and profitability webinar hosted by Holmes and Sackett.
Understanding the effects of temperature on pasture production and matching the supply of nitrogen to plant demands could mean there is potential to either hang on to stock longer or even restock to a greater extent.
Of course, the economics would have to stack up - there is no point in generating more feed if it isn't utilised, said livestock consultant Dr Jim Virgona, Graminus Consulting, Wagga Wagga.
Dr Virgona said while it was fair to say few people were short on feed at the moment, given the good rain and the fact most had lightened off stocking rates, there was potential for short-term feed boosts from nitrogen where it was warranted.
Feed boosts could come at a cost trivial compared to purchasing new stock at the moment, he said.
Given full soil moisture profiles, and what research has shown is possible in terms of pasture production under warmer winter conditions, there was some risk that producers might under-estimate the feed growth potential this year.
That could play into decisions around stocking rates but not really around lifting breeding numbers, Dr Virgona said.
He said it was difficult to predict the response to nitrogen.
"Many people quote 10 kilograms of dry matter for every kilogram of nitrogen added, but that really is just a rule of thumb," he said.
"A lot of people also ask, if I am doing everything right, why do I get a response to nitrogen in winter. The answer is that mineralisation has slowed to zero but there is still a demand for nitrogen in pasture growth."
The webinar outlined how temperature governs plant development and has a large impact on growth.
It showed pasture growth rates are closely related to temperature when other factors are controlled.
Research has shown pasture growth rates have lifted as temperature has increased over the past 30 years.
Dr Virgona outlined work modelling pasture growth in winter at four locations - Holbrook and Gunning in NSW and Mansfield and Hamilton in Victoria.
With the same farming system imposed, soil types constant and moisture eliminated as a limiting factor, weather data from 1961 until April this year was run.
The results show the median pasture growth rates from May to August in kilograms per hectare per day has increased significantly across all sites in the period from 1991 onwards.
For example, the median cumulative growth from May to August in the first period (1961-1990) at Gunning was 1879kg/ha. In the second period (1991 on) it was 2465kg/ha.
At Mansfield, 1973 kg/ha compared to 2527.
"We are heating up and the pastures know it," Dr Virgona said.
The message is if you are looking at expected growth rates as temperatures drop in winter where there is moisture, there is a risk of under-estimating.
"The point is, it's getting warmer and that has implications for nitrogen," Dr Virgona said.
Temperature independently influences two processes: demand, which is how fast the plant can grow and supply, which is how fast nitrogen can be made available from soil organic matter.
Most nitrogen that a pasture sources in a system which is not reliant on applications of fertilisers will be from organic matter that is mineralised to an available form.
The rate at which it converts from organic matter to mineral nitrogen is important and that is sensitive to temperature.
"Pastures respond to nitrogen in winter when demand outstrips supply and it is warm enough for growth to proceed ," Dr Virgona said.
The story Feed boosts on the cards this winter for southern graziers first appeared on Farm Online.