Spray v granules study
Is foliar spraying of urea a cost-saver?
THE benefits of applying foliar urea to pastures are being assessed in a 12-month trial at the NSW Department of Primary Industries in Wollongbar.
In theory, spraying urea onto the leaves of the grass plant directly should be more efficient than traditional urea granules applied to the soil, and in recent years there has been an increasing interest in applying urea or other nitrogen based fertilisers this way.
Nathan Jennings, of North Coast Local Land Services, one of the research backers, said if it could be confirmed that there were benefits to applying urea as a foliar spray to short-term ryegrass and kikuyu pastures, “it would likely have a significant reduction in on-farm fertiliser costs, improve pasture production, and help with environmental concerns over nitrogen leaching or volatilisation”.
“Direct spray is perceived as more efficient because, with a foliar application, the nitrogen doesn’t have to move through the soil to the plant roots before it is taken up by the plant, rather the nitrogen is absorbed through the plant leaves.
“It is in the soil where a high proportion of the total nitrogen loss typically occurs such as volatilisation to the air, leaching beyond the root zone, or leaching under waterlogged conditions.”
Some basic studies over short time frames of one to three grazings have indicated that nitrogen application rates can be reduced to 40% if applied as a foliar spray compared to granular.
Other results have been more variable.
However, all the research on this has been on perennial ryegrass which has a higher plant density than short-term ryegrass, meaning that a short-term ryegrass pasture may result in a lower proportion of spray nitrogen being taken up by the leaves.
Mr Jennings said a study
❝Our theory is that tropical grasses should be able to capture even more foliar nitrogen.
— Nathan Jennings
that focuses on a tropical grass pasture such as kikuyu was important for dairy farmers on the North Coast.
“Tropical grasses always have a lot of green leaf or stem/stolons left after grazing and our theory is that tropical grasses should be able to capture even more foliar nitrogen,” he said.
“The study will also look at the effect of foliar nitrogen application on the pasture plants and changes in soil nitrogen levels by intensive grass and soil sampling.”
It is also likely this method of nitrogen fertiliser application would be applicable to other tropical grass species.
Equipment required for on-farm adoption already exists via a modification of an existing boom spray unit and there are companies making machines tailored specifically for this purpose.
Far North Coast Dairy Industry Group and Norco Foods are working alongside North Coast Local Land Services on the project, which is being managed by Mr Jennings (senior land services officer) and Dr Bill Fulkerson, a research and development officer with Norco Foods.
PROOF IS IN THE PASTURE: The trial results will provide significant benefits to the dairy industry.