Research findings signal a promising start for PhD student

22 May 2015

Jack Pronger
PhD student Jack Pronger is researching the seasonal water use of mixed-sward pasture systems under dairy grazing.

Preliminary findings from a research project at the University of Waikato could mean good things for farmers dealing with the effects of ongoing drought. 

Doctoral student Jack Pronger's research focuses on identifying approaches to increase pastoral drought resilience by using more diverse mixes of pasture species. He's comparing the seasonal water use of mixed-sward pasture systems (a combination of different grass, legume and herb species) with more traditional ryegrass/clover systems under dairy grazing.

"If there is increasing incidence of drought, farmers need pasture species that can access water deeper in the soil, and/or reduce paddock-scale water use while maintaining agronomic production," says Jack.

"Knowledge gained from researching paddock-scale water use could contribute to more efficient water usage of pastoral systems – which will benefit the economy down the track."

Jack has finished the first year of his three-year project. He is studying three pasture sites at Waharoa, near Matamata, where the eddy covariance technique is being used to measure the exchange of water and carbon continuously.

There are three different pastoral systems being studied: an old ryegrass site that was already growing on the farm; a new mixed-sward site; and a new ryegrass site. The mixed-sward system includes chicory and plantain (herbs), lucerne and white clover (legumes), and ryegrass, cocksfoot and prairie and timothy grasses.

"I started this project with two competing ideas in mind. The first was that a mixed-sward pasture system may be able to access water stored deeper in the soil and therefore use more water to increase dry season production. Alternatively, the mixed-sward may use water more efficiently and could therefore push further into dry periods before depleting soil water stores."

Initial findings are proving interesting. Prior to planting the mixed-sward Jack measured water use across all sites (all sites were ryegrass) and found no difference between them.

"Preliminary data analysis suggests that over the first 12-month period after planting the new pastures, there's been 5-6% less water used by the new mixed-sward compared to the new ryegrass. That translates into about 50mm of water over 12 months."

Production from both the mixed-sward and the new ryegrass were about the same, but the mixed-sward used less water, suggesting the mixed-sward is using water more efficiently to produce biomass.

"These preliminary findings look good for mixed-sward pastures but measurements will continue for another couple of years to see how it all stacks up in the long term."

So far, Jack has focused on water use. The next step is to bring in changes in carbon uptake from the eddy covariance measurements so that he can test his ideas about water use efficiency.

"In a couple of years' time, I'd like to be able to provide informed advice about differences in seasonal growth patterns, water use, and water use efficiency of mixed-sward pasture systems relative to traditional ryegrass systems."

Jack works in the Waikato Biochemistry and Ecohydrology Research (WaiBER) group at the University of Waikato, with his research supervised by Professor Louis Schipper, Dr Dave Campbell and Dr Mike Clearwater. He has received scholarships and support from the University of Waikato, DairyNZ and the New Zealand Agricultural Greenhouse Gas Research Centre. He is also the current recipient of the Flower Doctoral Fellowship in Agribusiness.

For more information on the University of Waikato's involvement at Fieldays, Click here