Trace elements at the local dairy

I spent my childhood on a farm in Paretai  in South Otago. We were a few kilometres out of Balclutha, not far from Telford, which is now a campus of Lincoln University. Our farm was the only sheep farm in a dairy area. Our neighbours were dairy farmers, the kids at Paretai school (all 26 of them) were from dairy farms, apart from my sister and two brothers, and everywhere we looked outside our property there were cows. This was fairly odd for South Otago which was (and still mainly is) a sheep farming area. Perhaps because of this feeling of being surrounded, of being in a minority, I developed a real antipathy towards dairy cows. They were slow, and smelly, their fields were scruffy, they lacked proper fences. Paretai is an area of very low lying ground bordered by the mighty Clutha River. Dairy paddocks were small and bounded by shelter belts of poplars, toetoe and flaxes. These shelter belts provided protection from the southerlies that roared in from the sea and also helped to suck up excess water from the fields (of which South Otago often has in abundance). I regularly take my family to Kaka Point, ten minutes down the road from Paretai, for beach holidays (and a change from the unrelenting flatness of the Canterbury Plains) and I am always struck by these small dairy fields as we drive through Paretai, so different from the monstrous fields that you find in Canterbury with their large pivot irrigators. I guess South Otago dairy farms don’t normally have to worry about irrigation!

Over the years, whenever I have looked at these shelter belts and hedgerows I have wondered what effect different plant species have on the paddocks? Are poplars better at drying fields than macrocarpa? Do toetoe provide more services for pasture growth that flax? Which species provide the best returns for the cows? Moving further afield, with large scale dairy diversions occurring throughout much of New Zealand there has been widespread removal of shelterbelts and/or replacement with many other species, including natives. What do these species offer in the way of services to dairy farms? Nick Dickinson (ecology) and Brett Robinson (soil science), with colleagues from Lincoln University (Jason Hahner, Zhong Hong-Tao, Bianca Das and Daniel McLaughlin), University of Canterbury (David Leung) and University of Parma (Marta Marmiroli), recently published a couple of papers (one in Agroecology and Sustainable Food Systems, the other in International Journal of Phytoremediation) that lookeDairy3d at these issues.

The group looked at what native plants in paddock borders might offer stock in terms of trace elements and whether this was different to pasture and more traditional paddock border plants. They also looked at the effect of these plants on drainage and soil fertility. Native foliage and soil samples from around these species were collected from sites around the base of the Port Hills as well as from the Lincoln University dairy farm near Springston in which an extensive native paddock border has been planted for five years. Over 20 native species were examined, such as monocots like cabbage trees (ti kouka), toetoe, flax (harakeke) and dicots like kanuka, wineberry (makomako) and black matipo. The native plants were found to selectively uptake rare trace elements like zinc, copper and cobalt. Native plants contained less nitrogen but contained more tannins than pasture grass and traditional border planted trees, like willows. Importantly, large differences in soil fertility were found between the native border and neighbouring pasture, elevated trace elements, higher levels of soluble nitrogen, and different architecture of plant root systems that allows for a change in flow of nutrients. Although these differences were by no means hugely different from pasture, these studies do suggest that, as well as adding diversity to an area, natives may provide small additional benefits for dairy farm productivity.

So next time I drive through Paretai I will have at least some partial answers to my questions even if it hasn’t changed my antipathy to cows!

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