A TRIAL at the Macalister Demonstration Farm (MDF) is providing hard data to help establish the value of gibberellic acid in boosting winter pasture growth.
The trial which commenced in late May was set up by Incitec Pivot agronomist Matthew Mahoney and involves pasture plots treated with different rates and different types of nitrogen, with Pro Gibb SG ‘plant regulator’ added to half the treatments.
Sumitomo Chemicals which manufactures and distributes ProGibb SG claims additional plant growth from this product, especially through the cooler months, by stimulating cell expansion resulting in leaf and stem elongation.
And they say applying ProGibb to freshly grazed pasture leads to rapid foliage growth.
Mr Mahoney said the multi treatment trial at the MDF was established on a clean, second year, high quality perennial ryegrass pasture using plots of five metres long and two metres wide.
Each treatment is replicated four times in a trial design involving three forms of nitrogen – normal urea, ‘coated’ Green Urea and the liquid EasyN.
Nitrogen application rates are at 0; 12.75kgN/ ha; 25.5kgN/ha and 51kgN/ha, with and without Pro Gibb.
Four replications of each treatment ensure accuracy in the results and all plots are outlined with roundup.
The trial which commenced on May 26 this year has so far yielded data from ten weeks growth over with two harvests on June 24 and then August 10.
Following each harvest the entire paddock was grazed and then mechanically topped and the next treatment applied within seven days of harvest.
A field day audience at the trial site on August 20 heard that conditions at the MDF since the trial commenced had generally been mild with some cold days.
Pasture growth was boosted by 7.4mm of rain within four days of the May 26 start date and a further 6.4mm of rain after the second treatment which would have helped wash the nitrogen into the soil.
Mr Mahoney said soil tests prior to the start of the trial confirmed a high rate of background N in the trial paddock, measured at 25kg N/ha in soil from the top 10cm, a fact he said might have some bearing on the initial yield results.
These showed a mostly positive response to ProGibb with all but one treatment producing higher yields.
Even so Mr Mahoney said the increases due to ProGibb were probably lower than he expected and could be a function of the levels of residual soil nitrogen at the start of the trial.
*Extract. Full report Stock & Land, September 3.
