Introduction: Soil Fertility for a Circular Economy

“Soil fertility is the ability of a soil to sustain plant growth by providing essential plant nutrients and favorable chemical, physical, and biological characteristics as a habitat for plant growth. Plant nutrients include the macronutrients nitrogen, phosphorus and potassium, sulfur, calcium and magnesium. Micronutrients are essentially boron, chlorine, copper, iron, manganese, molybdenum and zinc. Fertilizers are chemical or natural substance or material that is used to provide nutrients to plants, usually via application to the soil, but also to foliage or through water in rice systems, fertigation or hydroponics or aquaculture operations. Nutrient sources include chemical and mineral fertilizers, organic fertilizers, such as livestock manures and composts, and sources of recycled nutrients.“

(Food and Agriculture Organization of the United Nations, 2023)

Soil is a precious resource that needs to be well looked after. By studying it in a “hands-on” manner we can learn about it and how it should be cared for. Soil takes thousands of years to develop from parent rock – 10mm of soil takes between 100 and 1000 years to form. The exact amount of time taken depends upon the speed at which the parent rock weathers, i.e. is broken down into small particles. Weathering occurs through chemical, physical, and biological processes.
Soil forms the upper-most layer of the earth’ crust and is made up of inorganic and organic matter. The inorganic components are weathered rock, air, water, and minerals. The organic components include the decomposing (rotting or decaying) fragments of plants and animals. The spaces between the small particles that make up the soil are filled with air or water.

Living plants (e.g. algae, lichen) and animals (e.g. earthworms, moles, termites) live in the soil and improve aeration and drainage. Some organisms, such as bacteria, play an important role in converting plant foods or nutrients, e.g. nitrogen, into a form that plants can use to grow.

As plants and animals die and decompose, humus (or compost) is formed from their remains. Decomposition involves the breakdown of plant and animal remains into simpler components. As a result nutrients, which are essential for plant growth, are released into the soil. Decomposition is brought about by the action of decomposers which include bacteria, fungi, and earthworms. The process of decomposition is essential for the recycling of nutrients.

Humus or compost fertilizes and enriches the soil as it contains nutrients and improves the soil’s ability too hold water and air. Thus, nutrients in the soil are used by plants and animals and then they are returned to the soil when plants and animals die and rot. In this way soil plays an important role in the recycling of nutrients.
By making compost in our gardens we imitate nature and ensure that our gardens are healthy and productive. Compost returns nutrients to the soil, increases the soil’s ability to hold water and air, and prevents erosion by binding the soil.

The circular economy is highly dependent on the functioning of soils and land for the production of food and other biomass; the storage, filtration and transformation of many substances including water, carbon, and nitrogen; the provision of fresh mineral resources and fossil fuels; and the use of their functions as the platform for nature and human activities. Resource demand is increasing as a result of the growing human population. In addition to the shrinking availability of resources resulting from their unsustainable use in the past, our planet’s diminishing potential for resource production, due to a range of reasons, is leading to resource scarcity, especially in the case of depletable resources. As an economic system that focuses on maximizing the reuse of resources and products and minimizing their depreciation, the circular economy greatly influences, and depends on, soil and land management. The concise management of the resources, land and soil is thus necessary, to make a circular economy successful.