Gibberelic acid or GA (also called gibberellin) is a naturally-occuring plant growth stimulant that, when temperature and soil moisture conditions are right, kick-starts plant growth and cell elongation in particular. It has traditionally had niche usage in horticulture, and vineyards especially.
Research with Different Application Rates
Early research on pasture demonstrated that pasture growth could be sustained longer in autumn or commenced earlier in spring by applications of GA. However, it was expensive, and at the rates then being applied, the initial response was generally followed by a depression in growth, so that its benefit was seen solely in terms of its ability to alter the timing of available feed on the farm. The depression in growth was a result of the initial stimulation exhausting the plant’s store of carbohydrate in the roots.
However, more recent research has demonstrated that (a) much smaller quantities of GA than originally investigated (but still vastly higher than were contained in seaweed extracts such as Maxicrop) were also very effective, (b) at these rates (10-20 g/ha), several successive applications could be made without growth depression, and (c) it could be applied, and give responses, at virtually any time of the year. In addition, its cost has dropped dramatically with the entry of GA made in China.
GA applied by itself typically gives pasture a tall, spindly, yellowish look, although its nutrient content is generally little changed, as long as N in particular is applied in a form that can be rapidly assimilated by the plant. This is particularly important if multiple applications are being made. The addition of a second growth stimulant, triacontanol which specifically promotes cell widening and thickness, is likely to improve responses further.
Why it Works
These responses to GA on pasture raise the interesting question of why should this be so, if the plant contains its own GA anyway? The answer may be that it takes time and energy for the plant to recognise when conditions are suitable for faster growth, and manufacture sufficient GA to send the ‘go for it’ signal throughout the plant. Pasture plants evolved in a natural environment with no irrigation to avoid the risk of drought, so they have inbuilt self-preservation lag mechanisms. Foliar application of GA probably short-circuits this lag time.
Surely a Better Option than Palm Kernel
For pastoral farmers with irrigation or reasonably reliable rainfall, which means all dairy farms and many intensive sheep and beef properties, GA applied with foliar or suspension N appears to be a cost-effective means of increasing pasture production, far more so than buying in feed such as palm kernel, and avoiding the potential damage to New Zealand’s environment and reputation arising from the importation of this product, which is seen by some to be encouraging deforestation in South-East Asia.