Living Soil

In any agricultural or horticultural system, nutrients are removed from the system when crops and livestock are harvested and sold. Fertility can be built by either growing, or adding organic matter, but in essence this can be likened to supporting the soil micro-organisms to enable them to form associations with the root systems of plants.

One quarter of all species on Earth live in soils, providing the basis for all food production for the other three-quarters. Like all habitats, soils must provide the full range of conditions necessary for these species to survive and thrive. Until now most of us have not managed soils with their biology in mind, the life in soils ‘requires the same attention as above-ground biodiversity’. Biodiverse soils have potential benefits beyond healthy crops and higher yields: soil has contributed to a number of recent discoveries, including new forms of antibiotics and anti-depressants.
Soil is a combination of minerals, organic matter, air, water and living organisms. None can be taken in isolation, it is their balance that is important.

One teaspoon of productive soil can contain 100 million to 1 billion bacteria. Some bacteria convert organic matter into forms useful for plants; others break down pollutants. Some form mutually beneficial partnerships with plants, supplying nitrogen to plants which in turn provide sugar for bacteria.

Fungi are important for nutrient cycling, water dynamics, disease suppression and just physically binding soil particles together. Forming long thread like structures called hyphae, they convert hard-to-digest organic material into forms that other organisms can use.

Protozoa are aquatic single-celled animals that live in water filled pores and the film of water that surrounds soil particles. Living in the top 6 inches of soil they consume bacteria, releasing excess nitrogen in a form available to plant roots.

Nematodes are microscopic organisms, most of which are beneficial for agriculture. Living in the thin film of moisture that surrounds the soil particles, beneficial nematodes play an important role in decomposing organic matter and therefore the recycling of nutrients.

The feeding and burrowing activity of earthworms incorporates organic matter into the soil promoting decomposition and nutrient cycling. The tunnels they leave behind them provide channels for root growth, water infiltration and gas exchange. A review of nearly 60 different global studies has demonstrated that earthworms can increase yields in the absence of nitrogen fertiliser – by on average 25% [Willem van Groenigen et al (2014) ‘Earthworms increase plant production: a meta-analysis’ Scientific Reports]. However, earthworms do not only create good soils, they need good soils to live in. Even slightly degraded soils can affect worm populations.

Arthropods include centipedes, springtails and beetles. They can be grouped as shredders, predators, herbivores, and fungal-feeders, based on their functions in soil. Most soil dwelling arthropods eat fungi, worms, or other arthropods. Root feeders and dead-plant shredders are less abundant. Arthropods mix and introduce air into the soil, shred organic material and control the population of other soil organisms.

This is an important and diverse group of invertebrates that include snails and slugs. Many can have an adverse impact on crop production but some also play an important role in the decomposition of dead plants.

Plants influence soils by exuding chemical secretions into the soil from their roots. For example, buckwheat produces a chemical that increases the availability of phosphorus, an important nutrient. Other plants produce chemicals that stifle the growth of competitors. 

Don't Forget to Feed Your Soil

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Living Soils

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Soil Food Web

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Author: Jasmine Black

Producer Support

In 2015, Jasmine completed a Ph.D. in soil biogeochemistry investigating molecular carbon on a savannah-rainforest boundary in Guyana, South America. Before joining the Soil Association she lived in Japan, learning different organic farming methods, and taking part in a social project for the largest organic cotton company in Japan. She is now part of the Innovative Farmers programme, working with farmers and researchers to help progress sustainable farming methods. She also helps to coordinate and deliver our exciting calendar of agricultural events, from farm walks and technical seminars, to national conferences and the Future Grower’s program.

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