Permaculture Designers Manual
CHAPTER 8 – WATER IN PERMACULTURE
Section 8.17 –
Soil Erosion in Permaculture
As all else depends on a stable and productive soil,
“soil creation is one of the central themes of Permaculture.”
Soil erosion or degradation is, in fact, the loss of production and hence of dependent plants and animals.
Soils degrade in these ways:
Via wind: by dust storm and the blow-out of dunes and foreshores.
Via water flow: by sheet erosion (a generalized surface flow off bare areas and croplands), gully erosion (caused by concentrated flow over deep but unstable sediment), and tunnel erosion (sub-surface scouring of soils below).
Via soil collapse or deflocculation: following increased salt concentrations in day-fraction soils.
Thus, the placement or windbreaks, tree crops, and fast-spreading grasses stabilizes erosion caused by wind, while permanent crop, terracing forestry, and (in the case of gullies) diversion and spreader drains plus gabions help reduce or heal scoured areas.
Tunnel erosion may call for de-stocking, contour drainage, and the establishment or deep-rooted plants, while the problems of desalting need the combined factors or reforestation (to lower groundwater tables) following deep interceptor drains to cut off salt seepages in surface soils (More on this in Module 10 Unit 2 Dryland Strategies).
Erosion follows deforestation, soil compaction, disturbed soil-water balance (increased overland flow and rising water tables or sail seepages), overgrazing, plough agriculture on the broad scale, episodes of high wind s or rains in drought periods, or severe disturbance caused by animal tracks, roading, and ill-advised earthworks.
Insofar as landscape design is concerned, soil erosion repair is the priority wherever such erosion occurs.
Apart from the physical factors, no designer, or nation, can ignore the economic or political pressures that inevitably create erosion by requiring or permitting inappropriate land use and forcing production or over-production on to the fragile structure of soils.
Third world debt and western world over-production are both primary factors in soil collapse.
In a conservative society, the very basis of land use planning would encompass the concept of permitted or restricted use or soils, carefully plotted in regions following analyses of slope, soil stability, minimal forest clearing (or reforestation), and permitted maximum levels of crop production, or livestock density, following the procedures of good soil husbandry.
In assessing erosion in the U.K., Charles Arden-clarke and David Hodges (New Scientist I 2 Feb ’87) point out that “many of the recent outbreaks or severe erosion are dearly linked to falling levels of organic matter in the soil… the more organic matter there is in the soil, the more stable it is.”
This stability is because of good soil structure and infiltration of water; whereas an inorganic soil may break down under rain.
With the following increase in overland flow, most soils will then erode as rills or gullies, or the destroyed surface can powder and blow away without organic matter to bond it.
On many delicate soils (over chalks) the only answer is to replace crops with pasture or forests. Intensive arable use and winter cropping both create more erosion.
The very radical conclusion is that mulching, green manure; grass leys on rotation, hedgerows, and minimal cultivation are not only urgent but imperative.
Thus, “the time to examine the organic (farming) approach has passed, the time to adopt it has arrived.” (ibid.)
At long last, some scientists are saying that enough evidence is enough; we need to tum to known effective land management based on permanence and organic methods.
This will take the combined good will of farmers, scientists, financiers, and consumers.