Getting the best from gibb

At a field day at the Northland Agricultural Research Farm at Dargaville in late November, committee member and local farmer Kerry Chestnut, reported on a field plot trial on gibb applications which had been running there for the last two years.
“It’s potentially one of the biggest revolutionary products seen in the last 30 years,” he said.
“But there are so many things we don’t know about gibb.”
It could allow farmers to grow cheap, early grass if used in the right conditions, then feed losses later in the season with post-gibb depression could be mitigated by extending the grazing round.
“It can be a tool for tight spots to give you feed in a hurry,” he said.
While the growth control hormone, which is found naturally in plants, has been used in this country for more than five years he said there had been both good and poor results.
With the trial results so far, for every question answered another 20 were posed.
In 2014 a field plot trial was set up on the farm to look at single and multiple applications of gibb with or without nitrogen on pasture production. It found a single gibb application of 20 grams/ha along with 37kg N/ha in July produced 1066kg drymatter (DM) more than the control treatment. Nitrogen alone produced 539kg DM/ha more.
No greater pasture production was seen from repeat gibb applications without nitrogen and there was significant post-gibb depression after the second harvest. It was decided to continue the trial in 2015 to measure pasture production responses to gibb at three different times as well as repeat applications to a ryegrass-based pasture in a high nitrogen input environment.
A trial was done during winter and spring with nine treatments replicated five times on plots which were four metres by 1.5m. As well as a control, nitrogen was applied five times from July to October in the second replicate. Single applications of gibb in July, August and September along with nitrogen made up the next three plots. The last four had gibb applied in July and August, July and September, August and September, and July, August and September, all with nitrogen.
Then 30kg N/ha went on as Sustain granular immediately after harvest so all treatments received 150kg N/ha from July to October except for the control. ProGibb was applied at 20 grams/ha with surfactant three to six days after harvest, so there was enough leaf to absorb the chemical.
There were harvests every 28 days through August and September and every 21 days in October and November with plots mown and the grass weighed wet and samples taken for DM analysis.
The nitrogen-only treatment grew 2760kg DM more than the control, giving a pasture response of 18kg DM/kg N.
At the Sustain application cost of $625/tonne the pasture response to nitrogen came in at an average of 7.5 cents/kg DM plus application costs.
The July gibb-plus-nitrogen application produced an extra 608kg DM/ha, and based on gibb-plus-wetter costs of $13/ha this response cost 2c/kg DM plus application costs. The August application of gibb and nitrogen produced 409kg DM/ha more than nitrogen-only at a cost of 3c/kg DM plus application costs, and the September application an additional 458kg DM/ha again at 3c/kg DM plus application costs.
All these single applications of gibb suffered post-gibb depression so the total drymatter response over the trial period was similar to the nitrogen-only treatment. But two applications of gibb and nitrogen in July and September showed a total response 406kg DM/ha more than nitrogen alone at a cost of 6c/kg DM plus application costs. While production was very good in July and September, August and October production was significantly lower.
The next best performing treatment was the single July application with nitrogen at 201kg DM/ha, also produced at a cost of 6c/kg DM plus application costs.
Repeat applications might be used to delay post-gibb depression until October and November when surplus pasture might be available for stock.