Feeling the pinch? Not enough pasture to lamb on? Looking for a cheaper way to boost the growth of your pastures?

Look no further than gibberellic acid. Commonly known as ProGibb (commercial name), the product contains gibberellins, a naturally occurring plant hormone that stimulates cell elongation or growth. This hormone is depleted in cold conditions, so applying it foliarly in temperatures of 5-15 degrees can boost winter growth of pastures. Phalaris is the most responsive species.

Trialed in 2024 at our Rokewood pasture trial site, the evidence was clear – gibberellic acid is a cost-effective way of growing more grass in winter. GA and urea were applied to separate strips of phalaris on the 29th July 2024 after limited autumn and winter rainfall. After 4 weeks, GA produced 275 kg DM/ha more than the untreated pasture, and urea had no response in the first 4 weeks (Figure 1).

 

Figure 1. Average dry matter (DM) production (kg DM/ha) of GA and urea strips.

Economics

The poor response to urea after four weeks meant it was cost-prohibitive for lifting production at this time, however, the added nitrogen was not wasted and boosted growth in mid-spring. But even when comparing responses of urea at eight weeks and GA at four weeks, its cost in production of dry matter and energy is nearly triple.

After 4 weeks, the gibberellic acid cost 8 cents per kg versus urea which cost $2.09.

Table 1. Cost of measured responses to urea and GA at four and eight weeks in kilograms of dry matter and cents per megajoule of energy (MJ) and the equivalent grain cost at 100% and 80% utilisation.

Costs of responses	Urea at 4 weeks	Urea at 8 weeks	Gibberellic acid at 4 weeks	Gibberellic acid at 8 weeks	Equivalent purchased grain
Measured response      (kg DM/ha)	29	243	234	120	–
Cost per kg DM	$2.09	25 cents	8 cents	16 cents	44 cents
Equivalent cost per    tonne of DM	$2090/t	$250/t	$80/t	$160/t	$444/t
Cost at 100%   utilisation (cents/MJ)	19.3 cents	2.3 cents	0.7 cents	1.5 cents	44 cents
Cost at 80%   utilisation (cents/MJ)	24 cents	2.9 cents	0.9 cents	1.8 cents	56 cents

 

To read the full trial report – https://sfs.org.au/resource/boosting-phalaris-winter-growth-using-nitrogen-gibberellic-acid

This trial is part of the Innovative Mixed Farming Project funded by Meat & Livestock Australia.

Image: Gibberellic Acid response in a Phalaris Pasture Source: J Wettenhall, SFS