Digging into why our soil is unhealthy and how we can fix it
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In the natural world, mid-winter is a time of dormancy and faded, monochromatic colours. Fallen leaves litter the ground; broken twigs are soggy with moisture; and dampness infuses almost everything. The combination of dormancy and dampness create perfect conditions for decay, as summer’s growth is actively subsumed back into the soil, replenishing nutrients as part of the annual cycle of our temperate seasons. This decay is a necessary precursor to the resurgence of fertility and growth in spring.
But this is not a passive process. It is dependent on the activity of a wealth of organisms working away underground, breaking down detritus in to component parts and recycling all the nutrients back in to the soil. Earthworms are the most familiar of these. In Ireland, we have 27 different species of earthworm. They are so abundant in healthy soils that a greater weight of earthworms exists beneath the ground than the combined weight of cattle grazing above ground.
And an unfathomable diversity of other, mostly microscopic, soil organisms are also busy beneath the surface. These include soil-dwelling algae; probing fungal filaments; a multitude of microscopic protozoa; an assortment of millipedes, centipedes and beetles; miniscule, alien-like tardigrades, nematodes and mites, and copeopods, to name but a few.
Communities of good bacteria are actively processing and recombining molecules of carbon and nitrogen in to available nutrients that plants roots can then absorb, with the help of mycorrhizal fungi. Just as with the more familiar above-ground food webs, soil organisms are all interconnected in complex food webs too. Predators and prey, producers and consumers, each with a specialised metabolism and exact niche in the soil ecosystem. Each is a necessary contributor to the maintenance of healthy living soil.
Scientists are only beginning to properly recognise the complexity of soil biota and their essential contribution to life on earth. A 2023 review of existing research, published in the proceedings of the National Academy of Sciences, reveals that more than half of all the species on earth live in the soil. This includes everything from microbes to mammals, with a staggering 90% of fungi, 85% of plants and more than 50% of bacteria that live in soil.
In addition to the diversity of life in soil, the abundance of life is staggering too. Protozoa, for example, are tiny single celled organisms — so abundant that just one teaspoon of fertile soil can contain as many as a million of these tiny creatures. In fact, one teaspoon of healthy soil contains more living organisms than there are humans on the whole of planet earth. It’s as though the scientific world is catching up with the insight of poet William Blake, who wrote the following words in the early 1800s:
"To see a world in a grain of sand, And a heaven in a wild flower, Hold infinity in the palm of your hand, And eternity in an hour."
The health of soil biota has far-reaching implications on global food security, and soil also plays a massive role in climate change feedbacks. Soil management affects the biological processes that lead to soils either losing carbon to the atmosphere or sequestering carbon from the atmosphere. Healthy soil, with a full array of soil biodiversity, also helps in climate adaptation, by increasing soils’ resilience to the impact of floods and droughts. Hence protecting soil life and soil carbon is a crucial component of climate change mitigation and adaptation.
And yet, in the frenzy to maximise trade and generate ever-increasing profits, more attention is given to the use of fertilisers than is given to maintaining natural soil biota and associated fertility. Chemical fertilisers can dramatically reduce biological activity in the soil. Because soil biota plays a crucial role in holding soil particles together, any loss in life within the soil also impacts on its physical structure, leading to compaction, erosion, and loss of natural fertility, which ties farmers into a loop of dependence of ever-increasing quantities of fertiliser. Our mistreatment of soil life has been diminishing the natural capacity of soil to function as a vital living ecosystem that sustains plants, animals, and climate.
The impacts of agricultural fertilisers are not limited to impacts on soil biodiversity. Nitrogen fertilisers are responsible for around 5% of global greenhouse gas emissions — more than global aviation and shipping combined.
Agricultural fertilisers are also the largest contributor to declining water quality across Ireland, with nutrient pollution from intensive agriculture a key culprit. 40% of rivers in Ireland are overloaded with nitrogen, levels of water pollution that deprive aquatic invertebrates and fish of the oxygen they need to thrive, and hampering the efforts of all those trying to restore good health in our freshwater ecosystems. Intensive dairy, in particular, is linked with elevated nitrate levels detected in the South East and Midland and Eastern regions.
The last few years have seen a reduction in chemical nitrogen nutrient fertiliser use in Ireland, compared to soaring quantities at the turn of the century. The recent reductions are due in part to sectoral climate targets, and in part to a rise in prices as energy costs soared following Russia’s invasion of Ukraine in 2022. However, pollution from nitrates remains one of greatest challenges to the health of Irelands environment.
An environmental assessment just carried out for the fifth Nitrates Action Programme, in preparation, states clearly that there is no evidence that the measures proposed for regulating and reducing the use of nitrate fertilisers will reduce water pollution and restore good water quality.
Restoring soil health is a critical task now facing us all, in non-agricultural habitats as well as in agricultural systems. Innovative approaches to farming such as agroecology can benefit biodiversity whilst simultaneously building up soils’ natural fertility and resilience. This contributes to food security as well as a healthy environment. As we are discovering the complexity and fragility of healthy soil, the importance of protecting our soils becomes ever clearer.