Carbon, compost, and soil critters
Hannah Wood (she/her)
As a global community we are walking, possibly sprinting, into a climate crisis. We have too much carbon in the atmosphere and it is TURNING UP THE HEAT! This is no secret. People all around the world are feeling the impacts and desperately trying to find solutions. Fortunately, there are solutions living right beneath our feet. Humble, unassuming, and often taken for granted, the soil we walk on is much more than it first appears. From a microbiology perspective, there is a complicated and mysterious world down there home to millions, if not billions, of species. The abundance and diversity of life is almost incomprehensible.
Here in Aotearoa New Zealand there are a great variety of soil types. There are dark fertile soils, light sandy soils, yellow clay soils, all kinds of soils! In te reo Māori, at least 60 names for different soils exist. The physical nature of soil is usually characterised by its relative composition of clay, silt, and sand, the amount of air and water, and the organic content (living and decaying organisms). The chemical properties are also very important, namely the pH of the soil and the availability of nutrients like nitrogen, phosphorus, and potassium. All of these factors influence the community of living organisms in the soil and the subsequent nutrients available for plants. A soil rich in organic matter, and therefore carbon, will be dark, chocolatey, and full of life. Gardeners with rich soils often talk of the sweet, earthy smell and the wonderful texture: dewy, crumbly, and light.
To get a grasp on what life looks like in the great underneath I sat down with Dr Nicola Day, lecturer in plant and soil microbial ecology in the School of Biological Sciences here at VUW. “We’ve got all forms of life in the soil […] Bacteria, Achaea, Eukarya, microscopic and macroscopic things. There is a crazy amount of diversity.” Living organisms in the soil form huge, complicated food webs that use carbon and do incredibly important work. As Nicola explains, “one of the biggest and most important things that happen in the soil is decomposition. That is, turnover of organic matter and the recycling of elements. There is a huge network of critters that do this. A leaf would just sit on the ground [indefinitely] unless you had these organisms.”
Another important relationship in the soil is between plants and their mutualists. Mutualists are other organisms that interact with plants in mutually beneficial ways. To a soil ecologist, one of the most obvious connections is between plants and mycorrhizal fungi. These are a type of fungi which connect with plant roots and give them much greater access to nutrients and water. There is a lot of evidence that plants would not have been able to establish themselves on land without fungal partners. As Nicola explains, the ancestral land plants “didn’t have proper root structures and wouldn’t have been able to take up nutrients from the soil.” In exchange for these services, plants provide carbon sugars. It’s not just mycorrhizal fungi that partner up with plants, though. Plant roots “leak nutrients” and the zones directly adjacent to plant roots are full of microbial activity. “There are amazing things happening there right next to the roots because of all the sugar being excreted by the plant for microbes to munch on.”
As a researcher of global change biology, Nicola is also keenly aware of global warming and the climate crisis. I ask her what kind of impacts soil communities have on someone like me, a student in Te Whanganui-a-Tara. “Soils provide a big carbon storage sink. There is a huge amount of carbon in the soil, and we need to keep it in the soil. Anytime people till soil and it digs up the carbon, any time there is a fire, anytime we cut down trees and don’t put the carbon back into the soil; these [actions] affect us as a global community.”
It’s hard to talk about soils and not consider agriculture, when 95% of human food comes from the soil. This reliance has led to 50% of all habitable land on earth being used for agriculture. Extensive use of resources for human consumption puts a lot of pressure on wild species, who are always battling against habitat destruction. To rub salt on the wound, much of the agricultural land use is unsustainable, leading to dramatic degradation of soils.
Many modern agricultural systems grow vast monocultures (a single species, such as corn) and use intensive chemical inputs to exclude unwanted species and boost growth in the crop. A lot of heavy machinery is used to till the soil, and after the harvest the earth is usually left bare. Large chemical inputs lead to significant changes in the soil chemistry and pH, factors that many soil organisms are very sensitive to. Heavy machinery can compact the soil, destroying the soil structure and making it harder for soil organisms to live and carry out vital functions. Compacted soil is also less able to absorb water during heavy rainfall. This can cause both flash flooding during storms and overall drier land.
When the above ground plant life is severely reduced and the land is intermittently left bare, the food source for the soil organisms is also reduced. Carbon feeds the soil food web, and a permanent, abundant above ground ecosystem is much better at providing this. The UN estimates that 75 billion tonnes of productive agricultural soil is lost to land degradation every year. Even in Aotearoa, we lose 192 million tonnes annually. Much of it is just blown away in the wind or washed into the ocean during storms. If the trend isn’t reversed, the future of our food security may become seriously compromised.
Fortunately there are some wise people doing things differently. The National Māori Organics Authority has developed a framework for working in the māra, drawn from a wealth of ancestral knowledge. Six key kaupapa—whakapapa, wairua, mana, māramatanga, mauri, and Te Ao Tūroa—act as a starting point to guide the cultivation of growing Kai Atua, pure food. This approach puts healthy soils at the centre of a healthy community. Some similar principles are seen in the world of regenerative agriculture and organic farming, both of which are growing practices in Aotearoa. One simple idea, building up the carbon levels in the system and therefore giving back some of what you take, holds huge promise for feeding soil organisms and ourselves.
We may be broke, stressed out students living in an urban jungle, but we can still be part of the solution. Plus, getting involved could have some surprising benefits. If your landlord makes you mow lawns, sweep up leaves, or weed but you don’t know how to dispose of it—don’t worry, just put it back in the garden. The soil critters will thank you for it. If you don’t have a garden but wish you did, just look around the city. There are many community gardens and they want you!
I spoke with Murray Robinson, long-term member of the Miramar Prison Community Gardens, and he advised me that anyone is welcome. “We are incredibly tolerant. Just come along, start pottering around, eventually someone will sign you up and allocate you a plot.” If you don’t like growing vegetables, he says “there’s space for people to do whatever they like. Mow the lawns, make sculptures, plant daffodils.” It’s $50 a year to join and you get access to a shed full of tools, a plot or two of land, and a frost-free peninsular to make your gardening dreams come true. To build up the carbon content in their plots, people use all kinds of things—pony poo, wood chips, grass clippings, seaweed, and kitchen compost.
If composting in your own home doesn’t really appeal, you could consider lobbying Wellington City Council to set up large-scale compost facilities. You would have full support from Nicola, who believes large-scale composting is long overdue in Wellington city: “we could really reduce our carbon emissions and enhance our soil biodiversity and soil health by having municipal composting. It’s a win for everybody.”
Getting close to the soil might have major benefits for your own health too. Many microorganisms have coevolved with humans and produce compounds which can talk to our immune system. Mycobacterium vaccae, a common microbe in the ground, interacts with human immune cells to reduce stress. That’s just one example and there are countless more.
Soil critters are our friends; looking after their health will help yours, and can help us to care for the planet.
Compost at Miramar Prison Community Garden, photo by Dylan