Saturday, April 13, 2024

Don’t dismiss soil’s carbon offset role 

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It may not be carbon zero, but soil carbon can represent a significant reduction in GHG emissions, trust says.
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By Phil Schofield, chair of the Hawke’s Bay Future Farming Trust

In November, the Hawke’s Bay Future Farming Trust hosted the first annual Healthy Soils … Healthy Profits conference over an afternoon in Hastings. The conference was attended by 140 people from the agri sector, with eight key speakers and a panel that focused on the challenge: can farmers maintain and improve their soil health while maintaining profitable farming systems? 

The conference focused on highlighting practical examples of New Zealand farmers working to improve soil health and soil carbon, as well as international perspectives on whether there is the potential for Kiwi farmers to also generate soil carbon credits to offset farm emissions, as is the case in other countries – an important piece of the “profitability” picture. The trust believes this can be done.

However, this philosophy is challenged in a Farmers Weekly article by Richard Rennie, “Too much gas for grass to handle, study shows” (December 11 2023), which referenced research published in the Nature Communications journal. The argument was backed up by soils Professor Louis Shipper of Waikato University.

The paper argues that soil carbon is not able to offset all GHG emissions from ruminant farm animals. We know this is the case and agree. Based on modelled methane and nitrous oxide emissions (we can’t measure these at farm scale, so we use models like OVRSR to estimate them) there is no way a typical NZ pastoral farm can be carbon zero using only soil carbon as an offset. 

But this is not a reason to not explore soil carbon as a viable farm offset. It can represent a significant reduction in GHG emissions – carbon zero is another debate. 

Most farms will not be increasing livestock numbers, so methane and nitrous oxide emissions are going to be static at worst and possibly reducing based on improving animal performance. Therefore, any soil carbon storage is a net reduction in farm emissions and still very worthwhile.

The trust’s projects are about sequestering soil carbon, which has the potential to offset a significant portion of the total emissions. The rest of the offsets will come from trees and improved farm efficiency, and/or reduced livestock numbers.

Most would agree there is a significant lack of scientific evidence in NZ that tests how different farming systems affect soil health and soil carbon levels. Landcare Research (Manaaki Whenua) is running the 500 Soils Project, but in general the relationships between soil health, soil carbon, water holding capacity and nutrients are not well studied. 

Yet evidence does exist to show that improving soil management activity can have a big impact on all of these, and vice versa. Recently developed eDNA technologies have been used on the trust’s Carbon Positive project in conjunction with AUT at the LandWISE site near Hastings. This will help inform us of the microbial groups associated with improved soil conditions. 

A soil carbon benchmarking project, undertaken by the trust in conjunction with Paul Smith from Soil Carbon NZ, tested volcanic soils in Hawke’s Bay. The results suggested  that soil carbon was much deeper than previously thought – with testing at 30cm, 60cm and 90cm. And the initial findings on John Kamp’s soil carbon put in doubt the consensus that NZ’s soil carbon can’t be improved upon (outlined in a 2021 article in Bay Buzz).

The trust is also supporting a project called Farming for Carbon, which aims to use internationally recognised soil carbon testing protocols to evaluate a selected group of NZ farms that are under long rotation systems. 

The aim is to establish whether, from a market standpoint, soil carbon levels can be increased and sequestered in the soil to a level where they can be certified as soil carbon credits.

United States carbon project development company AEI has been involved with soil carbon for well over 20 years and has developed a protocol and methodology to certify credits to an international carbon registry, which trades carbon credits that could be used as offsets for future emissions. 

Therefore, despite the consensus that carbon zero is not achievable on NZ farms, this is not a reason to throw the baby out with the bathwater. Increasingly it is shown that farming systems can make a change to soil carbon levels through a change in farming system – the “how, not the cow” argument. 

Soil carbon stock measurements, if applied on enough of our pastoral farms, would help scientists better understand the relationship between management of land, pasture and soil and changes in soil carbon. This could tell us at what rate measurable soil carbon will increase or decrease – knowledge that could be widely applied for the benefit of all NZ pastoral farmers. 

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