Soil regeneration

Soil regeneration, as a particular form of ecological regeneration within the field of restoration ecology, is creating new soil and rejuvenating soil health by: minimizing the loss of topsoil, retaining more carbon than is depleted, boosting biodiversity, and maintaining proper water and nutrient cycling. This has many benefits, such as: soil sequestration of carbon in response to a growing threat of climate change, a reduced risk of soil erosion, and increased overall soil resilience.

Soil quality means the ability of the soil to "perform its functions." Healthy soil is a mixture of living organisms, organic matter, and inorganic material. Soil should have texture so that air and water can diffuse through the void spaces in the soil. Air and water typically make up half of the volume of healthy soil. Air and water flow are important for keeping microorganisms and root systems alive, transporting nutrients, and wearing down inorganic components.

Soil is integral to a variety of ecosystem services. These services include food, animal feed, fiber production, climate moderation, waste disposal, water filtration, elemental cycling, and much more. Soil is composed of organic matter (decomposing plants, animals, and microbes), biomass (living plants, animals, and microbes), water, air, minerals (sand, silt, and clay), and nutrients (nitrogen, potassium, and phosphorus). For optimal plant growth, a proper carbon to nitrogen ratio of 20–30:1 must be maintained.

Plants have a particularly symbiotic relationship with microbes in the rhizosphere of the soil. The rhizosphere is an "area of concentrated microbial activity close to the root" and where water and nutrients are readily available. Plants exchange carbohydrates for nutrients excreted by the microbes, different carbohydrates support different microbes. This symbiotic relationship maintains living biomass, primarily fungal, in soils which increases the carbon content of the soil.

Healthy soils are sites of decomposition of dead biomass. Macro- and micro-organisms assist with processes such as decomposition, nutrient cycling, disease suppression, and moderating CO₂ in the atmosphere. Dead plants and other organic matter also feed the variety of organisms in the soil. Organisms like earthworms and termites break down large pieces of organic matter and contribute to soil texture by digging open spaces within the soil. Biodiversity in soils creates competitive pressure that reduces the available niche for disease and parasitic organisms.

Soil degradation is a decline in soil condition caused by poor management practices. Soil degradation depletes fertility and reduces the ability of soil to host microbial, plant, and fungal life. One third of the globe's land has degraded soil, especially the tropics and subtropics with around 500 million hectares degraded. Soils can be degraded in four general ways:

Many agricultural practices can cause soil degradation. Tilling soils for planting is a common form of degradation. The upturning of soils makes them vulnerable to wind erosion. The use of farm vehicles on soils can also cause soil compaction decreasing the permeability of soils to air and water. The biological activity of soil can also be degraded by agricultural practices. Overgrazing results in the loss of plant roots in soils, which reduced both organic content in soils and inhibits the natural symbiosis between plants and the soil microbiome. The use of chemical fertilizer inhibits nitrogen fixing fungi and bacteria in the rhizosphere and increase activity of nitrogen oxidizing microbes, leading to an increase of nitrous oxide emissions from soil. The effects of agricultural soil degradation can create a positive feedback loop. For instance, the decrease of soil fertility as a result of mechanical degradation can be compensated with the use of chemical fertilizers, which decrease the rhizospehere's capacity to produce ammonia, which requires more fertilizer applications.

Urbanization can also cause soil degradation. The construction of urban environments frequently involves the compaction of soil and the sealing of soils under layers of concrete, asphalt, and other materials. Sealing materials also decrease the natural absorption of rain water by soil causing intensification of water run-off during storms. The increased flow of water causes soil erosion. Cities also concentrate pollutants that can leach into soils. The maintenance of aesthetic monocultures such as grass lawns can also have deleterious effects on soils. Biodiversity is lost in the rhizosphere as a result of monoculture. Practices such as frequent mowing also inhibit the development of deep root networks and the use of fertilizers and pesticides result in further biological degradation.