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Tuesday, 10 November 2020

Get smart about N-response with gibberellic acid

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With new regulations capping pasture nitrogen (N) applications to 190kg N/ha on the horizon, the focus now turns to making the most of the pasture production tools we have at our disposal – in this case gibberellic acid (GA). 

When the timing is right, using GA with N fertiliser application is a smart way for livestock farmers to improve the efficiency of their applications.  

Cooler temperatures in spring and autumn slow pasture growth rates, which may lead to feed demand exceeding supply. Nitrogen is commonly applied to boost pasture growth at these times and this is also when the naturally occurring plant hormone GA can provide benefits for pasture growth. In warmer areas of NZ, Express GA can also be used to boost pasture production through the winter months. Used either as a standalone product or in conjunction with N, GA is suitable for application where soil temperatures remain in a range from 7-16C.  

In spring on dairy farms, there is usually plenty of pasture available for the first grazing round, but pasture 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 into the grazing rotation sooner. 

As referenced by the trial data in table 1 below, one of the benefits of using GA in conjunction with nitrogen is an additive effect which further boosts pasture production. This suggests that there is potential to use gibberellic acid to achieve the same increase in pasture production, but with lower rates of N than when nitrogen alone is used. 

Table 1: Pasture response to GA and Nitrogen applications in spring

Treatment Rate  Mean Dry Matter Yield Kg/ha  Mean extra Dry Matter Kg/ha  Kg extra DM/unit of N applied 
Control - 781  - -
Urea 20Kg N/ha  1015 234 11.7
Gibberellic Acid Express 20g/Ha + 
Widespread 1000 25ml/100L 
1040 259 -
Urea + Gibberellic Acid 20Kg N/ha + 
Express 20g/ha + 
Widespread 1000 50ml/100L 
1285 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 Ravensdown’s Express® GA at 20g/ha (8g/ha GA active ingredient) to clean, recently-grazed pasture (1-5 days) when soil temperatures are between 7-16⁰C. To capture the advantage of the temporary boost in growth rate, the pasture should be grazed between 21-28 days following treatment. 

Quality counts 

Quality is important when it comes to GA, given there is potential for some powder formulations to leave un-dissolved residues in spraying equipment. To test the solubility of Express GA, Ravensdown commissioned an independent laboratory to compare it against another water-soluble granule of GA. 

Table 2: Solubility test results

Product  Solubility at 20g product/50L  Solubility at 5g GA/L (12.5g product/L)   
  Un-dissolved residue (after 5 mins)  Time to dissolve  Un-dissolved 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 GIBBERELIC 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 un-dissolved residues were detected from Express after five minutes at twice the recommended concentration. When tested at the recommended theoretical solubility of GA (5g GA/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 efficacy of Express will not be compromised when used as directed.

The practice of applying GA in a tank 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.

Ref Cotching et al 2013, THE STABILITY OF EXPRESS GIBBERELIC 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.

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.

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.