Maintain or increase soil carbon

Many farmers are looking for ways to maintain or increase their soil carbon stocks to help improve farm productivity and, potentially, reduce atmospheric carbon dioxide concentrations.

Many ideas have been circulated, and there’s anecdotal evidence that some work. Comprehensive research is underway, which will enable scientists to say with more certainty which practices work in New Zealand’s physical environments and farm systems.

Professor Louis Schipper from the University of Waikato explains where soil carbon comes from, why it’s important, and why increasing New Zealand’s soil carbon levels isn’t easy.

Transcript

Duration: 5:27

CARRIE GREEN:
Healthy soil contains plenty of carbon, nutrients and moisture to help crops and pasture thrive.

The carbon in soil is also an important factor in climate change.

Globally, there's more carbon in soils than all land based plants and the atmosphere combined.

So taking even a bit more carbon out of the atmosphere and into the soil could be good for the climate as well as your farm.

But losing soil carbon has the opposite effect.

Now despite what you might of heard, it isn't that easy to increase soil carbon in NZ. Why is that?


LOUIS SCHIPPER:
I think that farmers have a very complex operation.

They're trying to juggle, how do we maintain production, look after our animals and also have this broader responsibility of looking after the environment as well.

One of the difficulties of farming is that there is inevitably some losses of greenhouse gas emissions.

All organisms produce carbon dioxide through a process called respiration.

But that's only one half of the equation.

The other half of the equation is plants taking carbon dioxide out of the atmosphere through photosynthesis

into their leaves, down into their roots and it eventually ends up in the soil.

And so, we have these two big processes going on at the same time.

A small difference between the two, results in an accumulation of carbon in the soil or a loss of carbon from the soil.

Our key job is to find ways to increase the amount that is captured and decrease the amount that is released into the atmosphere.

So when we think about this balance of carbon dioxide going down into the soil and being re-released,

we have these two big processes of photosynthesis and respiration.

If a soil is bare, so there's no plants growing on it, you've reduced the capture of carbon dioxide, and you're reducing the amount that's going into the soil.

The micro organisms in the soil keep decomposing or breaking down the carbon that is in the soil and re-releasing it into the atmosphere.

So when you think about a bare soil you've effectively stopped carbon dioxide being captured but the micro organisms are continuing to pump out carbon dioxide.

Avoiding soils being bare and not having active photosynthesising plants on them, is something that you should look to do.

Another way that we're exploring is whether there are different species that we can add into the pasture mix,

that will have more or different kind of roots penetrating through the soil and increasing the carbon content of the soil.

We've been looking at things like plantain, chicory, tall fescue and it's really going to be about what plants are best where.

It's early days yet but there's some promising leads that increasing the diversity of pastures can increase the amount of carbon in soil.

In NZ we're really lucky because we've got really forgiving soils, we have year round growth, and a great climate.

What has happened is that we've built up large amounts of carbon in our soils in comparison to many other countries.

Additionally, we tend to farm in a way that there's always vegetation on the surface and we're not continuously cropping large areas.

As a result we've got really large amounts of carbon in most of our soils around NZ.

It can be quite hard to increase the amount of carbon that you have in your soil. There are practices out there that might be able to help.

And those practices will not only benefit the amount of carbon dioxide that's in the atmosphere and increase the amount of carbon that's in soil.

But if you can increase the amount of carbon or just maintain what you've got then you've got a healthier soil.

That's going to support the vegetation above it better, and it's going to have better environmental outcomes.

It might make that soil more resilient to external disturbances like droughts.

Keeping the amount of carbon that you have in soil is simply good farming practice.

CARRIE GREEN:
The aim is to draw carbon into our soil and keep it there.

But NZ soils are already naturally high in carbon, so adding more is a lot harder than some other parts of the world.

And even though we grow a lot of grass, that doesn't tell us our soil carbon is increasing.

In fact, latest data suggests it's been steady at best in flat land and declining in peat soils.

It seems to have increased in hill country soils but we don't know if that's continuing.

So what's important right now is holding on to the soil carbon that we have.

There's lots of research underway to explore how we can do this.

It's looking at actions like avoiding bare soils and planting diverse pastures to find out how they affect soil carbon under NZ's different farm types.

You can find out more about this research and NZ's different soil carbon levels at www.agmatters.nz

Research to fill the evidence gap

Scientists are exploring the effects of a range of farm practices on soil carbon stocks, across New Zealand's varied climate zones, soil types, topographies and land uses. Scientists are looking at both temporal variations, as long-term data are particularly important, and spatial variations, as soil carbon stocks can vary significantly even across a single paddock.

Recent and ongoing research is looking at:

  • The potential of greater plant diversity in swards for generally increasing soil carbon and for reducing losses during pasture renewal or production of supplemental feed.
  • Growing deep-rooted lucerne under irrigated and unirrigated conditions, including the influence of different grazing regimes.
  • Optimising production of supplemental feed to avoid carbon losses during crop establishment and return to pasture. This research also aims to identify soil carbon gains when carbon in supplemental feed is imported into the paddock or farm.
  • How integration of space-planted trees of different species affects soil carbon stocks in pasture systems.
  • Sunflower and bumblebee in paddock on regenerative agriculture farmWhether regenerative agriculture could increase soil carbon (small-scale pilot study at this stage).
  • Whether full inversion tillage during pasture renewal can bury and stabilise topsoil carbon lower in the soil profile, while carbon is rebuilt at the surface.
  • Using measurements and models to investigate how irrigation of grazed pastures influences soil carbon under different soil and climatic conditions across New Zealand.
  • Whether a higher water table below farmed peat soils decreases soil carbon losses by increasing the anaerobic zone.
  • Identifying which soils have the greatest potential to stabilise soil carbon (at national to farm scales) so that the most promising practices for increasing soil carbon can be targeted to those soils.

See Potential actions for more information. You can also read this New Zealand Geographic article on regenerative agriculture for a helpful summary on its potential impact on soil and the science that is underway to understand the interplay with soil carbon.  

Measurement is key

Complementing these research programmes is a new long-term national soil carbon study conducted at 500 locations around New Zealand, which will benchmark soil carbon stocks in different land uses and then monitor how those stocks are changing with time. Initial data will provide a national-scale picture of how much soil carbon is currently stored and, later, whether those stocks are increasing or decreasing.

Core sampling for soil carbon measurement

To accurately measure soil carbon, precise sampling methods must be followed.

Some farmers may wish to benchmark or monitor soil carbon stocks on their own property. However, the process for robust measurements can be difficult and expensive depending on farmers’ precise objectives. If you're contemplating on-farm measurement, see the Measuring soil carbon topic page.

Researching, benchmarking and monitoring in New Zealand are critical, because the factors affecting farmers' ability to maintain or increase soil carbon stocks in this country are unusual. Not only are our climate, soils and topography like few other places on earth, but our soils already hold comparatively high stocks of carbon (see the Soil carbon topic page for more information).

From this high starting point, it's much harder to increase soil carbon stocks than it is in some other parts of the world. Actions that might be succeeding elsewhere, won't necessarily work here.

Ag Matters will provide updates as the research and benchmarking/monitoring study progress. You can sign up to receive email alerts whenever new content is posted.