Thought leadership - Scientist Profile
With 4000 mm of rain pelting down a year and livestock sinking up to their knees in mud, South Westland offers a challenging environment for farming.
But farming there is not everyone’s cup of tea, including for former local Stewart Ledgard.
“I was originally from a dairy farm in Hari Hari. I suppose for quite awhile, including when I was at Lincoln College, I always had farming aspirations as opposed to research aspirations.
“It was certainly one of the options, although I was never that fussed on the wet-feet element of the Coast.”
Instead, as a soil scientist, he has been in the vanguard of the environmental movement to improve farm performance in New Zealand. His research has been particularly instrumental in the development of the Life Cycle Assessment (LCA) tool, which analyses the use of resources and quantifies the emissions of a product or system.
By considering all the contributing factors that go into making a product – all of the inputs including, for example, their production, transport and use, and how it affects the environment – its carbon footprint can be calculated.
Before all that, though, Stewart was at Lincoln, studying under the enigmatic Professor T W Walker.
“There were some great people there, who were very inspirational. Prof Walker was quite a known character, quite applied in terms of the research side and in thinking of things in a practical way.”
After graduating with his B.AgSci with first-class honours in 1978, Stewart went to work as a scientist at Ruakura, where he still is some 45 years later. In those days, it was part of the Ministry of Agriculture and Fisheries (MAF) research division.
A few years later he crossed the Tasman to study toward a PhD with CSIRO and at the Australian National University (ANU) in Canberra, knowing he wanted to focus on soils and nutrients.
“They were the world-leading group at that time in terms of legumes and nitrogen fixation, as well as the role of fixed nitrogen to agricultural systems.”
He was awarded his PhD in 1984 and, bonded to MAF, returned to Ruakura at a time when New Zealand was building its first nitrogen-fertiliser manufacturing plant, one of National prime minister Robert Muldoon’s “Think Big” projects.
Nitrogen cycling in agricultural systems
“The role of nitrogen fertiliser for agriculture was in its quite early days and was being tested and understood. I was heavily involved in that area, more from the agronomy and production side of things rather than where I’ve moved in more recent years into the environmental side of it.
“We were concerned with the timing of its use and how best to fit it into farm systems to get the best responses and the best animal production gains from its use.
“Before then, there was actually minimal use of nitrogen fertilisers on pastoral farms in New Zealand, though there was some use of it for cropping. It was more about understanding how to use it quite strategically within the system and only at a few key times of year when it was most valuable rather than now when it’s used more regularly on dairy farms.”
Traditionally, farmers had relied on nitrogen fixation from clover and other legumes, which had been the subject of Stewart’s PhD.
“Then I looked at the effects of fertiliser use on clovers and how you can manage systems to get the benefits from targeted use of fertiliser nitrogen while still managing and keeping the clovers in the system and keeping them putting nitrogen into it.
“Clover is probably the best adapted legume plant across all of New Zealand. The use of lucerne as a key legume has waxed and waned with pest issues and best fit to some locations, but it's still an important legume throughout the country. And there are some other ones like red clover, but it just doesn't persist, so it’s added to systems for short-term benefits.”
Nitrogen fertilisers have changed little since the 1980s, when urea was still the predominant additive on farms. But it was in that decade when background apprehensions about the environmental effects of nitrogen fertiliser became more overt, he says.
“Internationally, there were some concerns about high nitrate levels in groundwater and the effects on human health. At that time, those fertilisers were used quite strategically at relatively low rates, compared with currently.
“About a third of my time is still involved on the environmental impacts of nitrogen cycling in agricultural systems and looking at different mitigations to reduce that loss.
Using the Life Cycle Assessment tool
Stewart explains: “Then about 15 years ago, I became involved in the new area of applying life-cycle assessment as a tool for understanding the whole system and environmental conditions. It’s become rather dominated by carbon-footprinting, but it's wider than just greenhouse gases.
“It’s accounting for the environmental impacts in terms of water quality, air quality, other human-health indicators, their ecotoxicities, the resource use, such as the depletion of fossil energy and resources. But these days the climate-change element of it tends to dominate.”
Stewart helped build the LCA tool from its origins in Europe as a method of resource accounting into one focusing on farm-system inputs and environmental outputs. Since 2011, he has been adjunct professor at Massey University’s Life Cycle Management Centre.
The tool is complex with huge databases supporting it. It has now been applied to all of Fonterra’s dairy farms and is used by other dairy companies. too, as well as for Beef + Lamb New Zealand, and the Meat Industry Association. About every six months, the LCA is updated to account for changes in methodology internationally and aligned to the New Zealand greenhouse-gas inventory, he says.
“There’s a number of areas where we have to make some fairly simplistic assumptions and we’re always trying to improve on those. It’s now more a matter of fine-tuning.
“It’s good that farmers are now more accepting of the climate-change impacts of what we do. The industry has done well in accounting for methane separately as a short-lived greenhouse gas than the longer-lived ones. Few other countries have got to that level.
“There's always the tension that we need to make environmental improvements, but we don't have the benefits that some other countries do through subsidies to help with that, which has positives and negatives.
“It means there's a bit more flexibility for farmers to look at the options that are going to be more cost effective, but it does make it harder for them to bring in improved practices and mitigations, especially if they have got a cost. I'm certainly not against the principle of some cost on emissions or something that encourages their reduction, and we are making gains.”
Stewart enjoys visiting his old South Island haunts at least every year but says most of his work has been in the North Island and he is very settled on his 25ha farm outside Hamilton, on which he runs about 120 dairy heifers.
As a keen road cyclist, he can often be found taming the rolling hills of the Waikato with his mates. He also has a mountain-bike for exploring tracks around the country.
With retirement on the horizon, Stewart is working closely to ensure the next generation of LCA scientists – people like AgResearch scientists and modellers Andre Mazzetto and Shelley Falconer – on developing the next wave of LCA methodologies while also beginning to look forward to being a campervan nomad, exploring the haunts of his youth in Westland, while keeping his gaze always fixed on the paddocks and what the farming sector is up to.