Sustainable agriculture — getting more for less

Sustainable agriculture — getting more for less

University of Canterbury (UC) research shows that timing could be everything when it comes to getting the best results out of fertilisers in the dairy industry.

With growing awareness of the negative environmental effects associated with intensive use of nitrogen fertilisers, farmers are increasingly looking for answers on how to use fertilisers in a more sustainable way.

Nitrogen is critical to plant growth and reproduction, but the downsides of intensive use include nitrous oxide emissions and nitrate runoff into waterways. Current estimates are that only 30–40% of applied nitrogen is used by plants, so understanding how uptake and assimilation processes work is critical in the quest to find more efficient ways to apply nitrogen.

New research by UC Biological Sciences PhD students Jessica Roche and Qianqian Guo is throwing light on how plants such as ryegrass take up and use nitrogen during the grazing cycle. Ballance Agri-Nutrients, working with UC, provided funding for this research.

For growers and farmers, a key question is whether it is possible to reduce the use of nitrogen fertilisers without compromising production.

“Or to put it another way, can greater production be achieved with lower inputs? The goal for sustainable agriculture is to get more out for less,” says Professor Matthew Turnbull, who heads the UC School of Biological Sciences.

“What we’ve been trying to do, in association with Ballance Agri-Nutrients, is to start exploring this question by looking at the process of what happens to plants when you add large amounts of nitrogen, in terms of the uptake in roots and incorporation of nitrogen in the form of organic compounds in the plant.”

The PhD research has found a critical link between the physiological state of pasture directly after grazing and the ability of that pasture to effectively take up nitrogen fertiliser. Soon after grazing, ryegrass plants tend to have very little stored sugar. It is precisely these sugars that are needed for nitrogen to be taken up from the soil and converted into amino acids and proteins.

So, adding fertiliser too soon after grazing may result in a relatively poor uptake of nitrogen.

“We have ongoing work to investigate and identify the right timing for adding nitrogen. Is there a sweet spot? We suspect there probably is one, somewhere within that first week or two after grazing when the pasture has recovered yet still has that potential to grow fast with the addition of fertiliser.”

Most of the students’ work, which has also been supervised by Professor of Biology Paula Jameson, has been laboratory-based using hydroponic systems to enable close control of nitrogen input and to make it easier to study the process of nitrogen uptake by plants.

Professor Turnbull said the research would help inform the work of Ballance AgriNutrients on the farm.

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