A sneak peek to the life beneath our feet
Why Soil Health is Critical to Life on Earth
Soil is a fundamental and valuable natural resource that serves as the foundation for life on Earth. Soils are complex and essential ecosystems that are thought to contain a quarter of the world’s biological diversity. In a single handful of healthy soil, you can find 10 to 100 million organisms! Thousands of species of soil invertebrates and microorganisms provide vital ecosystem services that are necessary for agricultural sustainability and ecological functioning. Certain types of pollutants can be broken down or cleaned up, for example, some soil organisms are able to degrade organic contaminants and transform them to non-toxic compounds. Furthermore, soils constitute an important component of the carbon cycle. Healthy soils are the world’s largest carbon storage facility. Soils that are able to sequester carbon, will help regulate air and water quality and reduce greenhouse gas emissions.
Protecting our soils will return the favour
The United Nations adopted the 2030 Agenda for Sustainable Development, which sets out 17 ambitious Sustainable Development Goals (SDGs) globally with the aim of improving and sustaining life for the people and the planet. Though soils aren’t specifically mentioned in the SDGs, soils play an important role in delivering many of them (e.g. food security, water scarcity, climate change, biodiversity loss, and health threats), as they revolve around soil biodiversity and are closely linked to soil health. Despite these intimate connections, we often fail to notice how soil and biodiversity are intertwined. Ecosystems are living systems, which interact with one another and their surrounding environment.
Healthy soil is characterized by its ability to sustainably provide ecosystem services that are necessary for the quality of life on Earth – services which are made possible by the diversity and abundance of soil organisms. Fertile and biologically diverse soils allow us to grow a variety of vegetables and plants needed for good health and nutrition. Soil organisms make nutrients available for plants. Plant nutrition depends on the availability and balance of these essential nutrients, which again depends on the presence of these compounds in the soil. As a result, the more biodiverse the soil, the higher the nutritional value of our food.
It is important to understand that 95% of the food produced on Earth comes from soil, either directly or indirectly. While it can take between 100 – 1,000 years to produce 1 cm of fertile topsoil, without proper land management practices, only a few years will take to lose it.
Access to excess in plant protection might be a problem
Agricultural and forest resources are vital, economically, environmentally, and socially. Therefore, ensuring high-quality yields, while also ensuring agricultural productions are environmentally friendly, can be challenging. Plant protection methods involving chemicals are the most widely used in integrated pest management and diseases of plants. Approximately 2 million tonnes of pesticides are utilised annually worldwide, where China is the major contributing country. Needless to say, chemical treatment of plants has an impact on the environment.
Pesticides are now thought to be harmful to soil organisms too, other than just affecting us – the warm-blooded beings. Because runoff and pesticide drift are the most prominent causes of offsite pesticide movement, efforts to reduce this impact have mostly focused on minimising pesticide contamination of water and air. Pesticide contamination of the soil, however, has negative consequences for the biosphere.
In fact, overuse of chemical control mechanisms (pesticides, antibiotics, etc.) was identified by the Food and Agriculture Organisation of the United Nations (FAO) in 2019 as the most impactful practice that has been driving the loss of soil biodiversity in the last decade. Pesticides are frequently sprayed directly to soil as drenches and granules, and increasingly as seed coatings, therefore it’s critical to know how they affect soil ecosystems.
In essence, the impact of a single species on ecosystem function depends on the presence of other species, which in turn result from a complex web of positive and negative, direct and indirect interactions among the various species that collectively drive ecosystem services.
In recent decades, many terrestrial invertebrates have declined. Agricultural intensification has been identified as a primary driving force, resulting in habitat loss and agrochemical pollution. Some scientists have dug deep on this topic reviewing nearly 400 studies on the effects of pesticides on non-target invertebrates with egg, larval, or immature development in the soil. To comprehend how changes in soil biodiversity affect ecosystem functioning, it is necessary to consider not only whether the total number of taxa present is related to a function, but also how the reduction in the number of species that support a single function relates to the simultaneous loss of multiple functions.
So, overuse of chemical fertilisers and pesticides may cause loss of soil microbial diversity which in turn can have a significant impact on specialized functional capacity, such as potential nitrification and denitrification activities, greenhouse gas fluxes, but also pesticide mineralization capacity.
Who lives underground?
Soil organisms vary from 20 nm to 20-30 cm in body width and are traditionally divided into four size classes. Following the categorization introduced in FAO’s State of Knowledge of Soil Biodiversity report (2020) these are:
I. Microbes including viruses, bacteria, Archaea, fungi (20 nm to 10 μm) and Microfauna like soil protozoa and nematodes (10 μm to 0.1 mm) mostly live in soil solutions in gravitational, capillary and hygroscopic water, and participate in decomposition of soil organic matter, as well as in the weathering of minerals in the soil. Their diversity depends on the conditions of microhabitats and on the physicochemical properties of soil horizons.
II. Mesofauna (0.1 mm to 2 mm) are soil microarthropods (e.g., mites, springtails, enchytraeids, apterygota, small larvae of insects). They live in soil cavities filled with air and form coprogenic microaggregates, increase the surface of active biochemical interactions in the soil, and participate in the transformation of soil organic matter.
III. Macrofauna (2 mm to 20 mm) are large soil invertebrates (e.g., earthworms, woodlice, ants, termites, beetles, arachnids, myriapods, insect larvae). They include litter transformers, predators, some plant herbivores and ecosystem engineers, moving through the soil, thus perturbing the soil and increasing water permeability and soil aeration and creating new habitats for smaller organisms. Their faeces are hotspots for microbial diversity and activity.
IV. Megafauna (greater than 20 mm) are vertebrates (mamalia, reptilian and amphibia). They create spatial heterogeneity on the soil surface and in its profile through movement.
How to protect them?
Five years ago, following the European Food Safety Authority’s (EFSA) request, the Panel on Plant Protection Products and their Residues (PPR Panel) developed an opinion on the science behind the risk assessment of plant protection products for in-soil organisms. The scientific group was able to define seven vital ecosystem services that are driven by soil organisms, particularly in the agricultural landscape. These are:
- Genetic resources, biodiversity. In-soil organisms are extremely diverse and contribute highly to the biodiversity of agricultural landscapes.
- Education and inspiration, aesthetic values and cultural diversity. In-soil organisms support the formation of typical structures in agricultural landscapes, delivering aesthetic values, cultural heritage and sense of place. The aesthetic value of soils is widely acknowledged.
- Nutrient cycling. The cycling of nutrients in soils is the basis for terrestrial life. Dead organic matter from above and below-ground is degraded by detritivores and finally mineralized by microorganisms. Mineralized nutrients can be then taken up by plants.
- Regulation of pest populations and of disease outbreaks. In-soil organisms are valuable antagonists of soil-borne pests affecting crop-plant species and have the potential to control the outbreaks of plant diseases.
- Soil remediation, natural attenuation. In-soil organisms degrade a variety of compounds in soils and contribute to the natural attenuation of xenobiotic soil pollution, including pesticides and their residues.
- Soil-structure formation, water retention and regulation. In-soil organisms are important drivers of soil-structure formation and maintenance. The activity of soil organisms modulates aggregate formation, alleviates soil compaction and regulates soil water-holding capacity.
- Food provision, food-web support. In-soil organisms are part of the below-ground food web and are the link to above-ground consumers. They are providers of secondary production and support biodiversity at a higher trophic level.
Provided through agricultural soils, some key soil organisms are able to deliver all seven ecosystem services. Hence, EFSA’s PPR Panel proposed pesticide toxicity assessments on six target species or processes, to map them out clearly.
While the European Union and the United States (US) have different legal requirements and policies, when it comes to pesticide regulation, the subject of ecological relevance is fundamentally a scientific question. Studies evaluating pesticide impacts often use a narrow range of surrogate species that are easy to rear, identify, or study, while smaller and more cryptic organisms are rarely analyzed. In certain cases, the soil organisms that have been studied the most are known to be less sensitive to pesticides than others, implying that we only have a limited understanding of the extent of pesticide harm. For example, the European honey bee is the only terrestrial invertebrate that is subjected to pesticide ecotoxicological testing. The practice of utilizing the honey bee as a surrogate undervalues the harm that pesticides cause to many other species, like soil organisms.
Because risk management decisions under the current framework are seen as poorly defined protection goals, a science-backed petition document was addressed to the US Environmental Protection Agency (EPA) suggesting changes (including the development of “Soil Health Guidelines”) to invoke a “Soil Health” endpoint in EPA’s ecological risk assessment for pesticides.
The health and diversity of soil organisms is critical for agricultural sustainability, as they run vital ecological processes such as maintaining soil structure, nutrient cycles, carbon transformation, and pest and disease regulation. The analysis of different soil communities under the impact of agricultural interventions suggests a highly integrative pattern of interactions within each of these functions. This has led scientists to conclude more complex measurements are needed to define the quality and health of our soils. Further research in soil biodiversity (and bioindicators) will hopefully provide an integrated understanding of the complexity of these systems.
Our organisation aims to apply and develop innovative solutions that support the sustainability of agricultural production – be it biological plant protection, remote sensing solutions for fertilising, or growing cover crops, which are all smart investments in soil.