Anja Murray: Don't treat living soil like dirt
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Healthy soil is bustling with life. At this time of year, when many plants are dying back and leaves are falling to the ground, nature’s focus shifts to all that is going on underground.
There, a community of micro-organisms such as bacteria, fungi, and algae along with soil animals such as protozoa, nematodes, mites, springtails, spiders, insects, and earthworms are busily breaking down dead plant matter and recycling nutrients to maintain soil fertility. This hidden world of living organisms is what buffers soil against the winter weather and creates the conditions for a new cycle of growth next spring.
Microscopic bacteria and fungi break down leaves, dead wood and other detritus. They actively transform waste material into compounds that plants need to grow. Algae too are present in healthy soils, working on mineral components — bits of sand and gravel — to release nitrogen, phosphorus, potassium, calcium, magnesium and other microelements.
Webs of unseen fungal filaments help plants to absorb these nutrients by wrapping themselves around plant roots and simultaneously weaving through soil particles, connecting plant roots to the source of necessary nutrients such as phosphorus, nitrogen, and zinc.
Protozoa, tiny single-celled organisms, are so abundant that just one teaspoon of fertile soil can contain as many as a million of these tiny creatures. Together with all the other soil biota, the quantity of lifeforms in soil is staggering. Just one gram of healthy soil can contain billions of organisms and a handful of healthy, fertile soil, often contains more lifeforms than there are people on the planet.
Earthworms make an enormous contribution to healthy soils too, although they are so commonplace that we barely ever give them a second thought. In a healthy grassland pasture, there can be as many as four million earthworms per hectare, so many that together they weigh more than the cattle or sheep grazing above ground.
In Ireland, we have 27 different species of earthworm, all burrowing beneath the ground, chomping through vegetable and mineral matter alike, composting and mixing as they go.
Their burrows are held in place with a sturdy slime, allowing them to venture to the surface and pull bits of leaves back down into the tunnel where they shred them up and eat them. These burrows help to aerate the soil, giving a lightness of texture that in turn helps the billions of other microorganisms present in the soil to thrive, each with its own role in the microcosmos of maintaining soil fertility.
All these different elements — the earthworms and the millipedes and the microscopic fungal filaments — maintain healthy fertile soils. Without them, there would be no wild woodlands or farmland fields. Everything we know essentially depends on the self-sustaining assemblage of soil biota.
But when we come along with big heavy machinery, with ploughs, combine harvesters, JCBs and heavy tractors, soil can become compacted. This means that air spaces get squeezed out, and the many critters who can’t survive without air diminish, leaving the abundance and diversity of soil biota much reduced.
THE CLIMATE IMPACT OF...
Agriculture
When we spray soil with fertilisers, many of the soil organisms can’t cope with enhanced levels of nitrogen, so they die out when artificial fertilisers are applied. Even cattle and pig slurry can drastically alter the abundance of diversity of soil organisms, reducing overall diversity, fertility, and resilience over time.
When soil structure and soil biota are impacted by intensive farming methods, farmers are tied into having to use more fertilisers to attain the same levels of growth as before, trapped in a positive feedback loop of diminishing capacity of the soil to maintain productivity and increasing reliance on artificial fertilisers.
More and more fertilisers are now being used to enable the expansion of livestock production, with impacts on water quality and atmospheric greenhouse gas emissions. In Ireland, sale of nitrogen fertilisers increased from 275,000 tonnes in 1981 to 370,000 tonnes in 2019, and we now have the dubious accolade of having the sixth-highest level of fertiliser use per hectare among EU member states.
A major problem is that the use of inorganic fertilisers has been masking the declining fertility and productivity of soils. The degradation of soils in Ireland and across the world is a key threat to food security.
In Ireland, the key threats to soil quality are loss of soil organic matter, erosion, compaction and contamination. All of these pressures contribute to the declining fertility of soil and reduce the capacity of soils to store carbon. Before we talk about rewarding landowners for soil carbon, we need to look at the vast losses of carbon from Irish soils that are currently contributing significant quantities of greenhouse gases to the atmosphere.
Scientists and policymakers are beginning to recognise that if we are to meet the challenges of food security along with climate change mitigation and adaptation, we need to do a better job of looking after soil microorganisms and maintaining healthy fertile soils in the long term.
The solutions are many, depending on the land use and management. Well-managed grazing can be good for soils, whereas overgrazing can lead to soil erosion and compaction. Reduced disturbance eases the pressure on soil health.
Hectare by hectare, research has shown that organic farms store significantly more carbon in top-soil than non-organic farms, yet in Ireland only 1.6% of farms are organic, far lower than the European average.
There is an urgent and scientifically well-recognised need for soil protection. However, concerted attempts to bring in an EU Soil Directive have failed due to political resistance among the Council of Ministers at EU level. Giving legal protection to soil has been repeatedly blocked. Instead, at the end of 2021, the EU adopted a new EU soil strategy, an approach that is more carrot than stick.
Soil is a hidden world beneath our feet, a complex community of unseen beings upon which everything else in our world depends. It is high time we act to prevent soils from deteriorating further by acknowledging their value and vulnerability, by implementing measures to actively protect and restore this unseen sphere.
WHAT IS...
The Carbon Cycle
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