Addressing the issue of over-grazing pasture


Addressing the issue of over-grazing pasture

Thursday 21st April 2022

‘Over-grazing’ is a problem for farmers, but “rescuing” pasture through deferred grazing isn’t the answer, according to research for the Hill Country Futures Partnership programme.

Professor Derrick Moot of Lincoln University, who is leading several of the research projects for Hill Country Futures, is recommending farmers move to rotational grazing as soon as practical and minimise set-stocking to ensure pasture doesn’t become depleted in the first place.

The Hill Country Futures project is focused on the benefits of using legumes such as lucerne to overcome nitrogen deficiency in hill country farming. Researchers are measuring the response of pasture species and legumes to their environment with the aim of giving farmers confidence to invest in appropriate legume-base pastures for hill country areas – boosting yield.

The $8.1m Hill Country Futures Partnership programme is co-funded by Beef + Lamb New Zealand, the Ministry of Business, Innovation and Employment, PGG Wrightson Seeds and Seed Force New Zealand. It is focused on future proofing the profitability, sustainability and wellbeing of New Zealand’s hill country farmers, their farm systems, the environment and rural communities.

“I recognised that we will be telling hill country farmers about the best forages to use in particular places,” said Professor Moot. “That will see five to ten per cent of a property being put into specialist crops but to really see benefits you also need to be getting the other 90 per cent right.

“Farmers will also often say the new cultivars are not persistent but a major part of pasture persistence is grazing management.”

Professor Moot saw that a review of grazing management would fit with a key research theme of the programme, looking at biodiversity in forage landscapes. He presented his review paper on this at the Resilient Pastures Symposium in 2021.

“We are seeing a lot of people now advocating for deferred grazing and leaving pasture to get long to allow roots to recover.

“They are getting successes – that is because pastures have previously been overgrazed and by doing so, they are not as resilient and so vulnerable to drought and pests.

“When a plant is grazed, you remove the green leaf, just like when you mow a lawn. To replace that leaf, the plant has to use its reserves, from above ground and from its roots. If we graze a plant too frequently, we reduce its reserves.

“The answer is for farmers to move to a rotational graze as soon as they can in the year, to give the pasture plants a chance to recover root reserves between grazing events and also to grow more feed. If you manage pasture appropriately, then there is no need to go to that state of deferring grazing or letting grass grow long and producing low quality tag.”

To achieve healthy sustainable pastures, Professor Moot says it is also critical to understand the biology of the plant you are using.

“For instance, if using ryegrass, you need to know that it needs to have three green leaves before you graze it. If you don’t do that, you deplete the reserves and if you do it more than once, the problem is compounded. Ryegrass is the most sensitive of our pastures grasses to mismanagement.”

Professor Moot says the leaf is the ‘solar panel of the plant’.

“It’s how the plant obtains carbon from the atmosphere, and if a plant is short of carbon, it tries to grow more leaves and doesn’t put carbon into its roots so the roots get weaker. If you keep grazing or cutting, it is constantly trying to catch up and grow new leaf and its root biomass will decline.

“The opposite happens if the plant is short of nitrogen or water. It reduces its leaf areas and puts more of the carbon into its roots. So as soon as you get a dry pasture, the plant grows more roots and stops growing leaves.

“These are the two stress responses and if you still keep grazing it, you put more and more pressure on the plants. It’s a double whammy of reduced leaf area and weakened roots. Set stocking results in constantly removing leaves and depletes the plant’s reserves.

“A golf course is a very good example of the most intensive grazing management possible – it is cut every few days. It has to be continually provided with nitrogen and water because the plants have got such weak root systems they can no longer forage for it.

“Take the example of St Andrew’s in Scotland, the oldest golf course in the world. The grass there is dominated by Browntop, which is also our most common grass in hill country. The reason it is dominant in both is that it copes with intensive defoliation either by a mower with an engine or a mouth and four legs, but Browntop is not a productive pasture plant.

“If we want to get rid of Browntop and introduce other forages, we have to recognise that we need to maximise rotational grazing and minimise set-stocking as much as possible.”

Professor Moot’s presentation to the symposium can be viewed at: https://www.youtube.com/watch?v=59t_VL3SGZg&t=3s&ab_channel=NZGrasslandAssociation

 


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