Jay Clarke, Horowhenua

Growing fruit and vegetables contributes to New Zealand's agricultural greenhouse gas emissions just as livestock farming does. At Woodhaven Gardens near Levin, Jay Clarke and his family have been figuring out how to reduce their impact on the climate. 

Learn how Jay Clarke and his family have been getting to grips with greenhouse gas emissions on their Horowhenua vegetable farm.



Like many vegetable growers, Jay Clarke and his family didn't think too much about agricultural greenhouse gas emissions. But Jay was concerned about the wider environmental impact of the family business and set about finding out more. He learned about a powerful greenhouse gas that's linked to a basic input on most farms, and he discovered that by changing how he applied his input, he could make a big difference to his emissions. Let's take a look.


All these lettuces, when I was a kid on the farm, we planted every single one by hand. We used to go around with a water tank on the back of a trailer, an old alloy water tank with three hoses that came out of it. And we'd sit on a bench seat, my mum, my sister and I, my dad would be driving the tractor, and we'd squirt a little bit of water on every single plant, just enough to keep it alive. And if you missed one, you've got in all sorts of trouble. Now we've got mechanical transplanters. We've got automatic irrigators that take themselves up and down the row. Huge amount of change that we're seeing.

Vegetable growing is a complex undertaking. And it's complex when you're doing it for one crop, let alone doing it for 24. Our thousand hectares isn't one single farm, it's spread out over 127 paddocks, with 50 kilometres between the most northern block and the most southern block. So the logistics of the business is hard. We've had to tackle different things, in different ways, in different locations. And as any good farmer will know, making environmental progress starts with knowing your property, so we've had to know 127 different properties. That in itself was a challenge.

When it came to emissions, we didn't know anything about it, and I don't think too many vegetable growers did know what it meant. We were lucky enough that we got approached by Massey University. They started stepping us through and talking about where our emissions hotspots could be.

The number one place, for vegetable growing, is the use of nitrogen fertiliser and nitrous oxide. That was actually really good for us, because it meant we were getting a two-prong approach. We were already looking at nitrogen around freshwater quality, and having a lower impact on surrounding waterways. So by tackling nitrogen for fresh water quality improvement, we've also been able to lower our emissions.

For us it's about bang for your buck. It's about producing the most amount of food for the lowest amount of emissions, or the lowest amount of fertiliser use. That comes in multitudes of ways that you can tackle that.

Precision ag is one of the biggest and readily available for people. So we went out and GPS'd our whole production fleet of tractors, so that when they're operating in a paddock we're making sure that any of our inputs go exactly where we want them to, that we're not getting fertiliser in parts of our farm that we don't want. So, for example, the control traffic tramway behind me, there is no crop growing there so we don't want any fertiliser there. So just coming out, broadcasting fertiliser everywhere, doesn't work for us.

Another way that we've addressed it is through increased soil testing, a thing called a quick N test. It enabled us to start doing nitrogen testing then and there, and understanding the exact requirements of the crop, how much nitrogen we had in the soil, and then being able to apply the exact right amount, at the right time, in the right place.


We start focusing on it the past two years. It's a pretty simple process, that we can just take some soils in the fields and then just test it in the labs or in the office, to know what is the amounts of nitrogen left in the soils to feed our crops. I will say every crops we have different practice, or different amounts needed to grow the crops and in different seasons as well. And sometimes look at the weather. Sometime we notice that if we have a lot of rainfall coming, we might not put the fertiliser before the rain, because we know that it probably going to leach.


The number one tip is know your product that you're growing. Do your research, find out what your crop demand actually is, and understand its growth cycle. That's got to be your number one; so be an expert in your crop.

Number two is use soil testing, use the tools like a quick N test to tell you how much you do actually have in your root zone, because you might have a whole tonne, you've just had a big mineralisation event and there's all of a sudden a whole lot of nitrate underneath. Or you might've leached and lost a whole lot. So knowing what's under there is really powerful.

And number three would be precision ag, enabling you to put the right product, at the right place, at the right time. It's an expensive step, but it's a step that farmers, once they take, they see so much value in it you'd never go back. Once you go down a track where you're using GPS across your whole system, your fertiliser placement will follow your planting placement, which means you can get the fertiliser really close and tight to your root zone.

There's other things that we would call precision ag, like being able to put fertiliser into the soil profile right next to the root by using fert boxes on our transplanters or on our sowers. And then into things like irrigating. So moving away from pipe to travelling irrigators that that have a higher degree of accuracy in that water placement.

For an industry that was probably guilty of saying, "We grow veggies, everybody bloody loves us, so therefore we don't have to do anything," we've actually shown that there's a lot that we can do. And there's huge improvements that we can make.

I never thought we'd get as far as what we did. We've at least dropped our electricity by 50%, and we've dropped our fert use alone by 50%. Never thought we'd get that far. You know, I thought maybe if we got 5% or 10% improvement that'd be great. But by a whole lot of little things, and it's no one big thing, I think it's a bit of an attitude towards it all, and in being willing to try different things and look at things differently, and not just doing it because that's the way you got up and did it yesterday. We've been able to add those all up and have a really major impact, and it's something I think we can be proud of.


So, Jay learned that growing vegetables contributes nitrous oxide emissions from nitrogen fertiliser, and carbon dioxide emissions from lime or dolomite. By optimising fertiliser use in his operations he has been able to lower emissions and improve the farm's impact on nearby waterways.

Jay and his team work hard to produce the most amount of food for the least amount of fertiliser. They know their crops. The soil is regularly tested for nitrogen, to work out whether more is needed. And precision ag is also key, meaning fertiliser can be applied exactly where it's needed, at the right rate, and at the right time. But what have the results of all these actions been?

Over the past three years Jay has almost halved his fertiliser use, leading to significant reductions in nitrous oxide emissions. At the same time, water quality impacts from fertiliser are reduced. This change in nitrous oxide emissions is the equivalent of taking over 300 cars off the road every year.

But this hasn't come without financial cost to the business, and the Clarkes are still working hard to understand if these new levels of fertiliser use are sustainable across all seasons in the longer term. Jay says their production has dropped by about 10% over this time. Jay and his family have shown that by understanding your environmental impact, and committing to change, even in small steps, it can make a big difference.

You can find out more about measuring, managing, and reducing your agricultural greenhouse gas emissions online.



About the farm

Woodhaven Gardens was established by the Clarke family in 1978 on the fertile plains of the Horowhenua region. The farm now grows 24 different vegetable crops across more than 1,800 hectares. It employs around 250 staff and, annually, the business sells 27 million individual vegetable units - about 10% of the national supply. 

"Vegetable growing is a complex undertaking, whether you're doing it for one crop or 24," says Jay, son of Woodhaven's founders John and Honora Clarke. "Our business isn't one single farm; it's spread out over 127 paddocks with 50 kilometres between the most northern and southern properties. In order to understand our environmental impact, we've had to get to know all those paddocks individually."

Getting to grips with greenhouse gas emissions

Like many vegetable growers, the Clarke family didn't know anything about agricultural greenhouse gas emissions when they started out, but achieving good outcomes for their business, the community and the environment was always front and centre. 

Broccoli paddock with people picking and a tractor

Broccoli picking at Woodhaven Gardens (Photo: Dave Allen Photography)

Their journey to understanding their emissions began when they were looking at ways to reduce nutrient leaching. They were approached by scientists at Massey University who helped them understand the impact of nitrogen fertiliser not only on freshwater, but also on the climate. 

Nitrous oxide is a potent and long-lived greenhouse gas that comes from a range of sources, including farming. In agriculture, it is emitted into the atmosphere when micro-organisms in the soil act on nitrogen introduced either by animal urine or dung, legume plants or nitrogen-based fertilisers. Methane is another powerful greenhouse gas emitted from farming livestock. But for most horticulture growers, the focus is on nitrous oxide emissions from nitrogen fertiliser use.  

"Figuring that out was actually really helpful for us because it meant we were getting a two-pronged approach," says Jay. "We were already looking at nitrogen for freshwater quality. By tackling that, we've also been able to lower our greenhouse gas emissions."

For horticulture producers like the Clarkes, greenhouse gas emissions are directly linked to nitrogen fertiliser use. A small amount of carbon dioxide is also emitted from lime or dolomite use. Horticulture New Zealand and MPI have developed a simple Excel spreadsheet that calculates the emissions from a horticultural operation. You can find out more on our Knowing your numbers page

The Clarkes' greenhouse gas numbers

In 2019/20, Woodhaven Gardens emitted 588 tonnes of nitrous oxide, expressed as 'carbon dioxide-equivalent' - just under half what they emitted two years prior, and the equivalent of taking over 300 cars off the road. 

(Carbon dioxide equivalent describes the amount of carbon dioxide emissions that would provide the same warming effect over a specified period of time as the gas in question, in this case nitrous oxide). 

Graphic showing tonnes of nitrous oxide emissions: 1060 in 2017/18; 790 in 2018/19; 588 in 2019/20

Nitrous oxide emissions from Woodhaven Gardens, 2017-2020

On-farm actions

The team at Woodhaven Gardens works hard to produce the most amount of food for the least amount of fertiliser. Here are the main things they've been doing to manage their nitrogen use: 

Tractor in a ploughed paddock with a planting unit on the back planting leeks

Planting leeks at Woodhaven (Photo: Dave Allen Photography)

  • Developed expertise in the crops they grow - understanding each one's growth cycle and fertiliser requirements.
  • Regular soil testing (via a Nitrate Quick test) to find out how much nitrogen is already in the root zone. 
  • Investment in precision agriculture systems to ensure fertiliser is applied exactly where it is needed and tight to the root zone, at the right rate and the right time. 

"We GPS'ed our tractors so we know that our inputs go exactly where we want them to, and we don't get fertiliser in the parts of the farm that don't need it," says Jay. 

The Clarkes also pay attention to the health of their soil, using crop rotation and cover crops to further minimise the need for fertiliser. 

"I never thought we'd get as far as this," says Jay. "But by changing a whole lot of little things, and being willing to try different things, we've been able to add it all up and have a major impact. It's something we're really proud of."

Jay says they are continuing to learn as they go and there are still parts of the system that need work, including monitoring whether the new, lower levels of fertiliser are sustainable across all seasons in the longer term.

For more on the impact of reducing nitrogen fertiliser, see our on-farm actions page

Know your numbers and have a plan

By the end of 2022, all farmers and growers will need to know their annual on-farm greenhouse gas emissions and by the end of 2024, they'll need to have a plan in place to manage them. These requirements are part of the He Waka Eke Noa partnership and are intended to help get farmers ready for agricultural greenhouse gas emissions to be priced from 2025. To find out more on how to do this, see our Know Your Numbers page