Spelling pastures
To build resident populations of subterranean clover in hill country pastures, sheep farmers are encouraged to spell selected areas for four to five weeks over late spring and early summer if possible.
Dr Racheal Bryant from Lincoln University was involved in the study which compared gibberellic acid and nitrogen and found dry matter could be increased by 300 – 400kg per hectare as a result of applying one application of gibberellic acid at the start of August. This was similar to increased dry matter production from applying nitrogen.
The findings of the study will be shared with Southland's dairy farmers on May 15 at the DairyNZ Farmers' Forum in Invercargill.
Gibberellic acid naturally occurs in plants to activate and control growth, increasing in concentration as days get longer. While exact numbers are not known, it's not widely used by New Zealand dairy farmers because, up until now, there has been very little research and information about how to manage pastures that have had gibberellic acid applied.
Dr Bryant says gibberellic acid works differently to nitrogen by increasing the size of each grass plant (or tiller) rather than increasing the number of grass plants.
"Whereas nitrogen will increase the density of tillers in the pasture, gibberellic acid makes each tiller bigger by elongating the leaf and stem. Applying either nitrogen or gibberellic acid can increase the amount of pasture in spring, but when gibberellic acid and nitrogen are applied together, you get the benefits of both increased tiller size and tiller number, which equates to more grass."
However, Dr Bryant says there are also downsides to gibberellic acid, such as reduced grass growth after grazing due to more leaf area being removed during grazing, and because the plants may have depleted soil nitrogen and water for regrowth.
"Until this study there wasn't a solution to this particular problem. Now we know the best way to manage this 'con' is by applying nitrogen before or with the gibberellic acid and allowing the grass to sufficiently regrow before being grazed again."
She said the research aimed to give farmers more options for improving pasture growth, including reducing the use of nitrogen fertiliser, knowing what the options would cost, and better understanding how to manage pastures that have had gibberellic acid applied.
"For example, if a farmer has nitrogen restrictions but wants to increase production, then gibberellic acid could be an option by applying it to mixed grass and clover pastures in early spring when growth is limited by cooler temperatures. Clover also has a very good response to gibberellic acid."
In terms of costs, Dr Bryant said gibberellic acid was a very favourable option – even when applied in conjunction with nitrogen – equating to around 12 to18 cents per kilogram of dry matter.
"It is cheaper than hay which can cost more than 50 cents per kilogram of dry matter, it's a better option than supplements in both cost and nutrients, and you're usually only looking at a one-off application during that 'pinch period' when you need more feed to get through calving," said Dr Bryant.
DairyNZ chief executive, Dr Tim Mackle, said each year the Farmers' Forum provides a great opportunity for dairy farmers to see how their levy is invested and to learn about dairy industry research and development work relevant to their region's farming issues.
Farmers can view the Southland forum programme and register to attend online atwww.dairynz.co.nz/farmersforum. Registration is essential and free to levy-paying farmers and their staff – there is a $50 charge for all others. The Farmers Forum is on May 15 at the Ascot Park Hotel in Invercargill and runs from 9.30am-2pm. Lunch is provided.
