Aaron Wall


PhD Student,

Research funded by the NZAGRC has had an unexpected benefit for PhD student Aaron Wall – the farmer’s son from the Waikato has learned a lot more about the realities of farming, while in return his work has helped his family understand the value of the NZAGRC’s research programmes.

Born and raised in Otorohanga on the family dairy farm (his parents now run dry stock and grow maize), and from a wider family of dairy farmers, Aaron already had a grounding in the primary sector when he began his journey towards a PhD in 2011.

He was employed by the University of Waikato to provide technical support to an NZAGRC research project looking at the impact of diverse swards on soil carbon change.

In 2016, the project’s lead scientist (Susanna Rutledge) left and Aaron took on more responsibility in his role. One practical aspect of the work being done within the project is on-farm measurements at paddock scale where the management is controlled by the farmer.

It's from this that Aaron really widened his perspective on the interplay between science and farming.

“I’ve spent a lot of time on farms observing while doing the fieldwork and talking with the farmers. Even though I’m from a farming background myself, these interactions have opened so many science ideas/possibilities that I wouldn’t have considered before.

“One of the things I value the most from my work (and my PhD research) is this opportunity to both learn from and help educate the farmers on the topics we are researching. In many ways much of our experimental designs (and in some cases research direction) have come from these conversations – and its only through being on farm regularly that this has been possible.”

Aaron had previously completed a BSc and MSc at Waikato majoring in Earth Sciences as a prelude to his PhD, which saw him taking on more data analysis as his work on the NZAGRC programme expanded.

“One of our research directions within the NZAGRC programme was looking at how supplemental feed affects the carbon balances of dairy systems. This was the focus of my PhD,” he says.

“Specifically, I looked at how both importing and producing supplemental feed (essentially an import or export of carbon) affected the carbon balances of these systems. I found that importing large amounts of supplemental feed (~50% of the animals’ diet) resulted in a small, but positive carbon balance (a gain of carbon to the farm), while measurements made from two years of a maize silage crop showed a big loss of carbon.

“My PhD also involved making carbon balance measurements from another dairy farm where supplemental feed imports were much smaller. This provided (1) a contrasting management and (2) allowed me to test a method to use the eddy covariance equipment (crucial to make carbon dioxide exchange measurements as part of the carbon balance method) to determine the carbon balances of individual paddocks, rather than a larger area where we’d previously been taking measurements.

“I was able to determine that the farm with lower supplemental feed imports had an average carbon balance of zero (no gain nor loss). The main findings could probably be summed up as this -- importing supplemental feed will only lead to only small gains in carbon, while the production of this feed can cause a large net loss of carbon from the ecosystem (paddocks).”

The new method to calculate carbon balances from two individual paddocks is now being used in a separate NZAGRC project looking at change in soil carbon stocks in soils under maize cropping. As part of this, the team has looked at how an alternative supplemental feed method (in-situ grazing of turnips) compares with using maize silage. The ultimate goal would be to identify the method of supplemental feed production/use that has the least impact on the carbon balance.

Aaron is now working for the University of Waikato, running another NZAGRC-funded research project. Current research areas are aiming to answer the following questions:

  • Does the carbon lost under maize silage cropping get regained after a return to pasture?
  • Can plantain decrease nitrous oxide emissions when used on a commercial dairy farm and measured at paddock scale?
  • What is the carbon balance of in-situ strip grazing of a summer turnip crop?
  • What are the measured greenhouse gas emissions from grazed pastures?
  • What are the greenhouse gas emissions from maize silage?

The data obtained from this work will help build a better picture of how management affects the carbon and/or greenhouse gas balances of dairy systems, and hopefully identify opportunities to mitigate emissions from these systems by modifying management.

Aaron cites one example – “While we are pretty confident maize silage results in a loss of soil carbon, if this is gained back over a number of years, that would suggest over a long-enough time period, rotating maize silage crop paddocks around a farm might be more beneficial than continuously cropping in one location (where the soil carbon stocks would be expected to be much lower).”

As with Aaron’s PhD, Professor Louis Schipper is the lead for this research. Having worked with him for the past 11 years, Aaron says Louis is “very supportive, while pushing me to improve, whether in the research support role, as a PhD student or now as a researcher.”

He also values the support received from NZAGRC, “the funding has allowed me to progress my career in a direction I may not have otherwise gone.”

Aaron is looking forward to gaining further understanding of the impact of common day-to-day farming practices as he continues his research career.