Most of Victoria experienced an extremely dry autumn. Agriculture Victoria says when rain does fall, soil temperature may become the main factor limiting pasture growth.
Agriculture Victoria livestock industry development officer Nick Linden says soil temperature, like moisture and fertility, plays a major role in controlling plant growth.
“Covers will stop fixing much nitrogen below about 9°C, which can provide some opportunities for response to urea,” he said.
“Research in Tasmania shows that perennial rye-grass continues to grow down to about 5°C, while annual rye-grass as low as 2°C.
“Australian phalaris has been shown to also grow down to about 5°C and a ‘guesstimate’ for more winter active cultivars is between 1.5 and 2°C lower.”
Mr Linden said urea and gibberellic acid (GA) provide options to increase pasture growth when nitrogen and/or soil temperature is limiting, on the proviso that good soil fertility, perennial pasture species and soil moisture are present.
“GA is made naturally in plant roots during spring and stimulates shoot and cell elongation, promoting plant growth,” he said.
“The application of manufactured GA in winter stimulates plant growth and increases winter feed availability.
“GA should be applied when air temperature is between 5°C and 15°C, when natural levels of GA are low.
“Several producer groups have trialled using GA with or without urea and results have varied across sites and years, so it may be worth talking to a local group or agronomist for advice on what to expect.
“The response to urea will be slower than when pasture growth is optimal (ie. spring) but may be worthwhile.”
Resources
Options for improving winter pasture growth presented by Lisa Warn: https://youtu.be/wOv35qcQg7k
EverGraze calculator for responses to urea and gibberellic acid: https://www.evergraze.com.au/library-content/gibberellic-acid/index.html
Agriculture Victoria gibberellic acid use in phalaris pastures: https://agriculture.vic.gov.au/__data/assets/pdf_file/0008/560924/GA-Demonstration-Summary.pdf