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What we need to know about soils, including growing things at home

Barefoot farmer

Here’s an idea: Instead of investing millions of dollars into unproven technology, such as carbon capture and storage, why don’t we put more effort into proven and productive ways of locking up CO2 in soil? 

According to soil science and climate experts, the humble dirt beneath our feet can hold three times more carbon than the atmosphere. And it doesn’t just sit there inert; it is good for the soil, for water management and for flora and fauna.

Building soil carbon is part of what’s known as regenerative agriculture. Many Australian farmers are getting on with it but policy is falling behind.

In the federal government’s recent announcement of a multi-billion dollar drought resilience package, for example, there is no clarity about whether initiatives that improve soil carbon levels will attract funding, according to director of Carbon farmers of Australia, Louisa Kiely.

“We just don’t know,” she told The Fifth Estate.

What is known at the grassroots level is that regenerative farming that builds up soil carbon can help protect farms from entering drought for longer and allow them to emerge from drought sooner than farms that follow a more chemical-dependent, industrial land management approach.

It is also not clear whether the $2 million funding over four years for Soils for Life announced by the federal government’s at the Bush Summit held in Dubbo recently will benefit carbon farming, Kiely says.

In his address to the summit, Prime Minister Scott Morrison highlighted the role soil carbon can play reducing emissions and improving farm productivity.

He cited National Soils advocate and former Governor General, Major General Michael Jeffery’s comment that one gram of soil carbon can carry eight times its weight in water, which means remediating soil to increase its carbon content essential to water management policy.

What does it all mean?

Increasing soil carbon is a form of emissions mitigation that comes with a raft of benefits, including tasty food and healthy landscapes, but Kiely says challenges remain, such as how farmers can connect with global carbon markets.

Australia’s government-driven market mechanism, the Emissions Reduction Fund, has sown few seeds, despite soil carbon potentially being one of the largest carbon markets in the world for the next 25 years.

There are also now verified international methods for measuring soil carbon sequestration, which means Australian farmers can fulfil international demand for carbon credits.

Some Australian carbon neutral initiatives may also deliver a windfall, such as the Meat and Livestock Association’s target of a carbon neutral industry by 2030.

Kiely says if the MLA wants Australian farmers to be offset providers, it could influence the deployment of drought resilience funding towards soil carbon initiatives.

Carbon Farmers Australia (CFA) is having its conference and expo next week in Albury, and among the speakers are international experts in regenerative farming, carbon markets and soil from countries including the UK, US, Canada and Nepal. Kiely says one of the goals of the gathering is to help Australian land managers succeed in the global market.

One of the problems CFA wants to solve is the “lack of a farmer focus” in many of the carbon accounting methods, Kiely says.

“We need a strategic, structured protocol,” she says.

Any patch of ground can do its bit

Rural and regional landscapes are not the only soils where carbon can be sequestered. According to soil expert and University of New England researcher, Annette Cowie, any patch of ground not covered by concrete, tarmac or bricks can store carbon.

That means parks, nature strips, backyards, front yards, verges and other open spaces are potential tools for climate change mitigation. Even plants in pots on an apartment balcony can lock up some carbon.

The problem has been poor land management in Australia has allowed organic matter – carbon – to decline. This impacts the ability of soil to provide the plants we rely on for food and fibre, and its capacity to provide other services including ensuring clean air and clean water.

High tech approaches to food cultivation – for example, growing vegetables in test tubes – might work in some circumstances but are unlikely to provide energy-dense foods like rice, wheat or potatoes, Cowie says.

At a very basic level, looking after soil and increasing its organic matter is a more feasible way to keep us all fed.

Building soil quality also helps remove carbon from the atmosphere. As plants grow, they lock up carbon as plant matter decomposes.

The humble urban compost heap can do its bit too, she says. The important thing is to ensure it is not a wet compost that releases methane as it matures by keeping it well-turned.

Cowie has been engaged with UN-driven research around the potential uses of biochar, charcoal created from organic feedstock under controlled conditions to reduce the emissions it generates as the charcoal is made.

On the ground projects have included trials with coffee growers converting their production waste into biochar and then using it as a soil amendment.

In Australia, a system has been invented using a pyrolysis technology in a shipping container than can turn woody weeds – trees and shrubs in the wrong place – into biochar.

Cowie says in China this happens at scale, with all plant residues now used for pyrolysis to generate energy and soil amendments.

In South Australia, herb grower Holla Fresh has installed ECHO2 technology developed by Rainbow Bee Eater that converts biomass into energy and biochar for its greenhouses.

Increasing use of biochar is a “low-cost, low-tech, easily-distributed option” for locking up carbon compared to some of the proposals for geosequestration such as the Otways facility, Cowie says.

One of the challenges for more Australian biochar plants is EPA regulations. They are a “bit allergic” to the concept, as if it is not made in an appropriate way it can release methane. Contaminated feedstock is also an issue, as it results in a contaminated product. There is also the danger of contaminating feedstock.

But done the right way, it can be a “win, win, win”, certainly compared with wilder ideas such as pumping iron filings into the sea to combat ocean acidification which is not only expensive but can have negative environmental impacts, Cowie says.

It’s not only recent pilots have shown the value of biochar. Some of the world’s best fertile soil, “terra preta”, is found in the Amazon, where the charcoal content of soils has been increased over decades by the Indigenous people.

A similar terra preta soil type has also been identified in Australia, and there is some research underway to understand the role of Indigenous land management practices in its formation and whether there are ways other soils in Australia’s temperate zone can achieve similar super-fertile qualities through carbon sequestration.

How to get started storing carbon at home

The big takeaway from for all of us is to look at our own backyards and balconies as potential soil carbon storage units.  Not only will growing some produce at home reduce emissions from food miles and have a bunch of other personal wellbeing benefits, it can also help directly suck up and lock up some emissions.

One important consideration for city-based gardeners though is the degree to which soil may be contaminated with lead or other nasties from sources including lead-containing vehicle exhausts and dust and flakes from lead-based paints.

Researchers at Macquarie University’s VegeSafe program have developed a map that shows which areas of Sydney have been shown to have the highest levels of contamination. The research team continues to expand the data too, with an ongoing citizen science initiative that offers testing of soil samples. 

You can send a sample of your soil and have it tested for metal contaminants, including lead. The cost is a suggested donation to the program of $20 or more for up to five samples.

Even without soil testing to clarify any contamination risks, there are ways you can garden that minimise the impacts of lead or other nasties.

Melbourne-based permaculture experts, Very Edible Gardens, have undertaken soil sampling around Melbourne and found results that mirrored an RMIT study showing one in five Melbourne backyards has significant lead contamination.

In advice specifically for gardening in lead-contaminated soils, VEG suggest that some crops are less risky than others. Fruiting plants such as tomatoes, pumpkins, strawberries, chilis, capsicums and fruit trees have the lowest risk of containing lead from the soil.

The riskiest crops are root vegetables, so wash well and always peel them before cooking or eating. Some leafy greens can also be risky, but The Fifth Estate notes these can be effectively grown in pots or raised wicking beds using a good organic potting mix and compost so you still store soil carbon while cultivating salad fixings.

Other helpful things VEG suggests include adding organic matter such as compost, as it helps bind lead up so less can be taken up by plants.

As the VegeSafe folks say – the key thing is to “carry on gardening”.

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