Healthy soils not only help us to maintain productive vegetation, but also support ecosystems and biodiversity, and help stabilize climate through storage of greenhouse gasses. In the landscape the benefits of healthy soil include improving infiltration, reducing runoff, reducing erosion, reducing plant water and nutrient requirements, filtering out pollutants and improving water quality, improving plant health and reducing their susceptibility to disease. We have often taken these important benefits for granted and most of our urban and agricultural soils have been eroded, compacted and depleted of their natural vigor.
There is a tendency to view soil as an aggregate of inert minerals which serve as a medium for plant growth and as a structural support for construction. Whereas this may be true of soils that have been heavily degraded and lost their vitality, healthy natural soils are far from lifeless. There have been estimates that a handful of healthy soil may have more living organisms within it than there are humans on the Earth. In terms of abundance and diversity of species, there is much more going on below the soil surface than above. The majority of these species have yet to even be identified, and they represent a tremendous untapped resources for mankind. Natural soils provide habitat for a variety organisms including plants, worms, insects, arthropods, bacteria, fungi, protozoa, and nematodes. These species form complex interrelationships and are responsible for decomposing organic matter, breaking down nutrients and making them available to plants, protecting plants from pathogens and disease, maintaining soil structure and stability, improving water storage capacity and converting or attenuating pollutants. Many coexist in symbiotic relationships with plants to fix nutrients like nitrogen and produce growth regulating hormones.
Healthy soils also help to reduce greenhouse gas emissions, by storing carbon and other greenhouse gases in the soil. Soils are believed to contain more carbon than the vegetation they support, and may hold twice as much organic carbon as the atmosphere. Organic soils also store methane and nitrous oxide, which trap more solar heat than carbon dioxide. When soils are disturbed, buy tilling, compaction and the use of chemical soil amendments, they surrender these gasses to the atmosphere, exacerbating global warming.
Reliance on chemical fertilizers and pesticides can weaken and destroy soil organisms. The destruction of soil organisms by fertilizers and pesticides reduces the natural capacity for decomposition, nutrient and waste processing, and resistance to disease and pathogens. Many non-target organisms are affected by chemical pesticides, including, not only soil microorganisms and non-target plants, but also fish, amphibians and birds. As these hazardous substances accumulate and work their way up the food chain, they can disrupt the balance of ecosystems harming many organisms, including humans.
Composting should be considered on any site where organic waste is produced. Not only is composting an excellent means of cycling nutrients on site, it diverts this material from the waste stream and reduces the burden of waste disposal. Compost and nutrients and improves soil structure, infiltration and water storage capacity and reduces runoff, erosion and sedimentation. Applying a layer of mulch to the soil surface can significantly reduce the germination of weeds, while conserving soil moisture.
The old approach to site development where the site is bulldozed and scraped clean of vegetation, exposing the soil surface of the entire site to the erosion and drying will need to be changed if we are interested in maintaining healthy soils and ecosystem functions. Soil preparation and management practices may include preserving and protecting native topsoil and vegetation where possible, restoring healthy soil components and function and protecting restored soils and maintaining healthy functions.
In areas that will be built on, healthy, existing topsoil should be collected and stockpiled for reuse on site. Measures should be taken to insure ongoing protection and maintenance of healthy existing and restored soils. We should avoid unnecessary compaction from vehicles, animals and humans. In areas where it may be necessary to have occasional access for vehicles, permeable paving can be provided, to protect the soil and vegetation from compaction and erosion. Designated, low impact trails or boardwalks may be established to limit soil disturbance from foot traffic.
Examples:
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Minimize the development footprint & restrict traffic in areas that will not be developed
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Protect the area beneath the drip line of trees and natural vegetation
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Stockpile topsoil during construction for reuse
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Provide footpaths and circulation corridors to minimize trampling of natural areas
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Restrict access of humans, pets and livestock to natural areas
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Install compost bins to recycle organic material on-site
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Organic mulch
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Organic fertilizers (milorganite, manure, compost)
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Eliminate toxic chemical fertilizers and pesticides
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Use non-toxic integrated pest management techniques (corn meal gluten)
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Restore natural soil flora & michorhyzae