Soil protection and restoration

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Revision as of 16:13, 1 July 2017 by Tom Henfrey (talk | contribs) (Begun with text from chapter 5.2 of Permaculture and Climate Change Adaptation)

Land degradation is a major cause of climate change, and degraded soils are much more vulnerable to its impacts. Declining, more erratic and/or extreme rainfall and increased rates of surface evaporation reduce available soil moisture, limiting plant and animal growth. Higher temperatures increase rates of mineralisation, reducing the soil’s capacity to sequester carbon and retain water. Other potential impacts include declines in organic matter and soil biodiversity, and increased rates of compaction, erosion, and landslides.1 Permaculture employs a range of techniques to reverse these spirals of decline: to increase the capacity of soils to store water, support a healthy underground biota, supply nutrients to plants, sequester carbon, and reduce greenhouse gas emissions, supporting both adaptation and mitigation. These techniques have in common that they mimic or enhance natural processes that help build and maintain healthy soils, using physical and biological methods. They are often combined with revegetation and creation of agroecology systems.


A common feature of forest gardens and other agroecology initiatives, no-till farming encompasses four broad, intertwined management practices beneficial for soil quality and adaptation of agriculture to climate change: minimal soil disturbance, maintenance of permanent plant cover, direct sowing, and sound crop rotation. Ploughing breaks up and inverts the soil: leaving it vulnerable to water and wind erosion, harming soil organisms, reducing productivity and increasing agricultural runoff; it also directly releases greenhouse gases. No-till methods cause negligible soil disturbance, opening only a narrow hole of the minimum width and depth necessary for planting. Residues from previous crops largely remain at the soil surface where they act as mulch.2


Another physical method is use of biochar, a coal-like material produced by burning fibrous plant matter at relatively low temperatures in an oxygen-scarce environment such as a kiln. 3 When buried in soil, biochar increases its capacity to retain water and nutrients and raises levels of microbial activity.4 Burning converts the carbon in biochar into a biologically inert form that can persist in the soil for thousands of years, meaning it also has great potential for carbon sequestration and climate change mitigation.5


Linking physical and biological interventions, Hugelkultur is a traditional eastern European planting method that many permaculturalists have adopted as a soil improvement technique. It involves covering woody debris with soil to create elevated plant beds that mimic nutrient cycling processes in natural woodlands. The decomposing wood in a hugelbed acts like a sponge, soaking up rainfall and gradually releasing it into the soil along with organic matter and nutrients, promoting mycelium development and improving the general quality of the soil as a habitat for microorganisms. This technique has been extensively used at Krameterhof Permaculture Farm in the Austrian Alps, enriching the soil and creating microclimates that extend the variety and growing season of cultivated plants.6


Regenerative Agriculture, a form of broadacre permaculture developed on the US prairies and now also applied on grasslands elsewhere, employs mob grazing (or multi-paddock grazing) for soil improvement. This seeks to mimic the ecology of highly mobile herds of wild grazers by putting cattle to graze at high densities in very small areas for very short periods of time, typically a few days.7 Grasses are eaten only to one third of their height and can regenerate rapidly once the animals move to another paddock. Partial die-back of the roots of grazed plants adds organic matter to the soil and initiates a positive feedback loop that supports soil regeneration: the soil improves, grasses grow taller and their roots deeper, and root decomposition following grazing takes place deeper in the soil. Livestock fertilise the soil with their urine and manure and partially break its surface through trampling, so nutrients are absorbed into the soil rather than being carried away by surface runoff of rainwater.8 Formal research has shown beneficial effects on pasture quality, soil microorganisms and water retention compared to continuous grazing.9 This confirms anecdotal reports from ranchers practicing mob grazing across North America,10 and practitioners who have used it to revitalise economically unproductive farms and restore degraded farmland to a state of productivity and health.11 At Polyface Farms in Virginia, USA, regenerative agriculture practitioner Joel Salatin has transformed soil depth and habitat quality while building up an annual revenue of over two million dollars from sales of produce, making it an outstanding example of a regenerative enterprise.12