A winter feed shortage could be looming because of the tough dry autumn. Urea and Gibberellic acid (GA) are well proven strategies to promote pasture growth in winter, provided there is adequate soil moisture.

SFS evaluated Urea and GA across new winter active phalaris varieties (18 months old) and run down Australian phalaris pasture to see how much additional pasture could be achieved at the SFS Rokewood pasture research site.

Urea applied at 87 kg/ha in late July 2023 produced additional growth averaging 160 kg DM/ha or 4 kg of dry matter for each unit of nitrogen used on the new phalaris. This was lower than reported responses in good pastures which have been as high as 12 kg/DM in August and 8 kg/DM, during June and July. The response at Rokewood was lower due to the new establishing pasture being less than 30% phalaris content with dry dying winter grass.

Gibberellic acid is a naturally occurring hormone that stimulates cell expansion resulting in leaf and stems becoming longer. It becomes depleted in plants during cold temperatures; therefore responses occur in winter.  Typical growth responses are 350 kg/DM of additional pasture for recommended rates. At Rokewood in 2023, the pasture grew only 100 kg of extra dry matter. The reason for the poor response is the biggest constraint to pasture growth is nitrogen and until that constraint is addressed, responses to other products could be limited.

Interestingly neither product increased growth of the old Australian Phalaris in the same trial.

The key message for producers is before applying these products, make sure that the soil fertility is adequate and apply them to your best pastures for maximum results. You may still get responses from a mediocre quality pasture, but expect less extra growth.

When trying to decide whether it is more economical to apply urea to existing pastures or to supplementary feed you can use a tool on the SFS website.  Urea priced at $800/t, cost 3.62 cents/MJME of pasture energy which was slightly cheaper than buying grain at $400/t and hay at $250/t, making it a worthwhile strategy if you need feed.  The only other factor to take into consideration is you need good soil moisture, if you have no soil moisture neither product would work.  To access the calculator and learn more visit https://sfs.org.au/resource/how-to-use-fertiliser-n-successfully-lee-menhennett-incitec-pivot-fertilisers.

 

Caption: 2023 Rokewood Trial Site 5 weeks after application on Sept 8, 2023 showing the deeper green colour of urea (on right) and the lighter colour of pasture that has been treated with Gibberellic acid (on left). Source: SFS.