Why gibberellic acid can be a magic bullet this autumn.
With regulations capping the amount of nitrogen (N) that can be applied to grazed pasture, it’s important to make the most of available pasture production tools such as gibberellic acid (GA). When the timing is right, using GA with N fertiliser is a smart way for livestock farmers to improve the efficiency of nitrogen applications.
Cooler temperatures in spring and autumn slow pasture growth rates, which may lead to the demand for feed exceeding supply. N is commonly applied to boost pasture growth at these times and this is also when the naturally occurring plant hormone GA can benefit pasture growth. Used either as a standalone product or in conjunction with N, GA is suitable for application when soil temperatures remain in the 7 to 16°C range.
In spring on dairy farms, there is usually plenty of pasture available for the first grazing round, but growth rates are often too slow for the second and third grazing rounds. In this situation, GA and N can be used to boost pasture growth rates allowing treated paddocks to be brought back earlier into the grazing rotation.
The table below shows that using GA in conjunction with N can further boost pasture production. It can also lower the amount of N needed than when N is used alone.
Table 1: Pasture response to GA and N applications in spring
|
Treatment |
Rate |
Mean dry matter (DM) Kg/ha |
Mean extra DM Kg/ha |
Extra DM per unit of N applied Kg |
|
Control |
781 |
|
||
|
Urea |
20 Kg N/ha |
1,015 |
234 |
11.7 |
|
Gibberellic Acid |
Express® 20g/ha + Widespread 1000 25ml/100L |
1,040 |
259 |
- |
|
Urea + Gibberellic Acid |
1,285 |
504 |
25.2 |
Ref: Jiang et al 2011 In: Adding to the knowledge base for the nutrient manager. (Eds L.D. Currie and C L. Christensen). http://flrc.massey.ac.nz/publications.html. Occasional Report No. 24. Fertilizer and Lime Research Centre, Massey University, Palmerston North, New Zealand.
Best practice is to apply GA at 20g per ha (8g per ha of GA active ingredient) to clean, recently-grazed (1 - 5 days) pasture. To capture the advantage of the temporary boost in growth rate, the pasture should be grazed between 21 to 28 days following treatment.
Quality counts
Quality is important when it comes to GA products, given that there is the potential for some powder formulations to leave undissolved residues in spraying equipment. To test the solubility of our GA product, Express®, an independent laboratory was commissioned to compare it against another water-soluble GA granule.
Table 2: Solubility test results
| Product |
Solubility at 20g product/50L Undissolved residue (after 5 minutes) |
Solubility at 5g GA/L (12.5g product/L) Time to dissolve |
Undissolved residue |
| Express® | <0.001% | 9 minutes | 0% |
| Alternative Brand | 0.003% | >30 minutes | 1.2% |
Ref Cotching et al 2013, Comparison of the solubility of two gibberellic acids for agricultural use, in accurate and efficient use of nutrients on farms. (Eds L.D. Currie and C L. Christensen). http://flrc.massey.ac.nz/publications.html. Occasional Report No. 26. Fertilizer and Lime Research Centre, Massey University, Palmerston North, New Zealand.
No undissolved residues were detected from our product after five minutes at twice the recommended concentration. When tested at the recommended theoretical solubility of GA (5g GA per L), Express® completely dissolved after nine minutes. The conclusion from these tests was that there should be no issues with the solubility of Express®, and the effectiveness of it will not be compromised when used as directed.
Quality also affects your ability to mix GA. The practice of applying GA in a tank to mix with dissolved urea is becoming more popular, as there are benefits from using both at the same time. The stability of Express® was tested for up to 24 hours after mixing with water and dissolved urea solutions containing 18% N.
Express® was stable (>98%) for at least 24 hours in all test solutions. Adding urea increased the pH of the Express® solution from 6.1 to 8.1. There was no difference in Express® stability when mixed with urea solutions with pH 4.5 to 9.
Table 3: Stability of Express® GA in combination with liquid Urea
Ref Cotching et al 2013, THE STABILITY OF EXPRESS GIBBERELLIC ACID IN COMBINATION WITH LIQUID UREA, in Accurate and efficient use of nutrients on farms. (Eds L.D. Currie and C L. Christensen). http://flrc.massey.ac.nz/publications.html. Occasional Report No. 26. Fertilizer and Lime Research Centre, Massey University, Palmerston North, New Zealand.
These results show that Express® GA can be used with confidence, the soluble granules are easy to measure and mix, and can be applied successfully with dissolved urea solutions.
Express® 20g/ha + Liquid N (20kg N/ha) + Widespread, right-hand side of the plot is the untreated buffer.
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