Words by: Jackie Harrigan

Effects of plantain-based pasture on milk production and nitrate leaching by dairy cows is being studied at Massey University by Vietnamese animal scientist and PhD student Nguyen Truong Thi.

Thi has come to Massey on a New Zealand government scholarship to do his doctorate before returning to lecture at the Danang University in dairy cattle production.

While both dairy systems and pastures in Vietnam are very different to NZ, he is keen to learn as much as he can from the NZ pastoral system, while learning about experimental design and research processes.

“When I go back to Vietnam, I can teach Vietnamese farmers and students,” Thi said explaining that dairying in Vietnam is divided into two systems – cut and carry of forage to small two-three cow family owned herds, who sell milk to locals, and three or four large dairy companies, who have much larger housed and concentrate-fed herds, and process milk into products for sale in stores and supermarkets within Vietnam’s towns and cities.

With Thi’s project, prior research has confirmed that plantain can reduce cows’ urinary concentration and the nitrate leaching from pastoral systems without negative effects on milk production. But the mechanisms by which there is a reduction in N excretion are not fully understood, nor are the influences on urine-N concentration and milk production caused by the differences in nutritive composition, digestibility and mineral content between plantain and traditional grasses.

Combining plantain with perennial ryegrass and white clover (RG/WC) is expected to provide dairy farmers with a sustainable option to address environmental issues without negative effects on farm productivity. But there is limited understanding of the long-term stability of plantain-based pastures and the relationship between the percentage of plantain in the cows’ diet and the N-leaching and milk production.

Thi’s research aims to quantify the effects of plantain-based pasture on the whole farm system N balance and farm productivity.

He will be testing the relationship between the proportion of plantain within mixed pastures and the N leached, urinary N excreted, pasture yield and milk production, and developing and evaluating methods to monitor this relationship on farms.

Experiment design sees 6.6-hectare rain-fed forage paddocks at Massey University No 4 dairy farm host grazing trials, with the area split into four pasture treatments (control 0%, 30% plantain, 50% plantain and 70% plantain – all cv. Agritonic) by five replicates. The trial is set up for measuring drainage from the hydrologically isolated plots (of 800 square metres each) and will be grazed by eight cows on a monthly basis (depending on grass growth).

Thi has collected data on herbage drymatter yield, milk production, N excretion from cows (post-grazing dung and urine samples), NO3 leaching from pasture plots, and measuring the N balance of the pastoral system. The experiment is designed to run over two full grazing seasons 2019/2020 and 2020/2021.

First year’s results

The first-year results showed plantain / ryegrass mixes as a viable onfarm option for reducing the nitrogen leaching while maintaining milk production from grazing dairy systems. The results show the potential benefit of incorporating plantain in ryegrass-white clover pastures as a natural mitigation option to reduce the urinary N loading from dairy cows and the N leached from the urine patches.

In an overall 80mm of drainage volume so far (winter-spring period), the total N leached has been 63% lower in the plantain/ryegrass/clover mixes with 30,50 and 70% plantain in the sward compared to the RG/WC clover pasture with 0% plantain.