Soil Rehabilitation in Permaculture

Permaculture Designers Manual

 

CHAPTER 8 – WATER IN PERMACULTURE

Section 8.18 – 

Soil Rehabilitation in Permaculture

 

 

Careful gardeners take care not to break up, overturn, or compact their valuable soils, using instead raised beds and recessed paths to avoid a destruction of crumb structure.

Responsible farmers try to govern the speed and effect of their implements in order to preserve the soil structure, and can get quit e enthusiastic about a dark, humus-rich, crumbly soil.

 

We seldom give farmers time or money to create or preserve soil but expect them to live on low incomes to serve a commodity market, whose controllers care little for soil, nutrition, or national well-being.

No matter on what substrate we start we can create rich and well-structured soils in gardens, often with some input or labour, and always as a result or adding organic material or green manures (cut crop).

No matter how rich a soil is, it can be ruined by bad cultivation practices and by exposure to the elements: wind, sun, and torrential rain.

Worms, termites, grubs, and burrowers create soil crumbs as little bolus or manure piles, and they will eventually recreate loose soils if we leave them to it in pasture.

 

But we also have other tools to help relieve compaction; they can be explosives, special implements, or roots.

We use the expansive and explosive method rarely, perhaps to plant a few valuable trees in iron-hard ground by shattering.

 

People like Masanobu Fukuoka are more patient and effective, casting out strong-rooted radish seed (daikon varieties, tree legume seed, and deep-rooted plants such as comfrey, lucerne, Acacias, and eventually forest trees.

Much the same subsurface shattering occurs, but slowly and noiselessly. The soil regains structure, aeration. and permits water infiltration.

A measure of the change wrought by green mamures, mulch, and permanent windrow is recorded by Erik van der Werf (Permaculture Nambour Newsletter, Queensland, Dec. 1985 and Mar /Apr 1986).

Working in Ghana at the Agomeda Agricultural Project, he reports on the improvement of crumb structure by measuring the bulk density (weight per volume ratio (g/cc) of soil samples) is given in Table 8.8.

 

We can use rehabilitative technology on a large scale, followed by the organic or root method, by pulling a shank and steel shoe through the soil at depths of from 18 cm (usual and often sufficient) to 30 or even 80 cm (heroic but seldom necessary unless caliche or compacted earth is all we have left as “soil”).

In field or whole site planning, a soil map delineating soil types can either be purchased or made based on local knowledge and field observation.

In designing, it helps future management if uses, fencing, and recommendations for soil treatment and crop can be adjusted to such natural formation as soil types.

An aid to SOIL TYPING can be found in basic books on soils. These publications give practical guides to landform, floristics (structural) typing, and soil typing and taxonomy (categories or classes of soils).

We can recommend low-tillage systems, pay dose attention to water control during establishment, and get soil or leaf analyses done.

We can also make careful trials of foliar sprays, the additions of cheap colloids to sands, the frequency and timing of critical fertilizer applications (often and little on sands, rarely or as foliar sprays on clays).

Crops suited to natural pH (it is often expensive to greatly modify this factor) and rainfall should be selected for trials.

Close attention needs to be paid to the soil stability and thus the appropriate use for soils on slope,

 

In particular, priorities should be set for erosion control in any specific soil or on specific sites or slopes, and earthworks or planting sequences designed to establish soil stability, for if we allow soil losses to continue or worsen all else is at risk.

The next stage in the design is to assess the capacity of soils for dams, swales, foundations, or specific crops (this may need further analysis, test holes by auger, or soil pit inspection).

 

Thus, if we have adopted a pre-determined set of values based on soil and water conservation and appropriate uses of sites versus erosion and high energy use, any site with its water fines and soil types noted starts to define itself in usages.

 

How we need to proceed in soil rehabilitation is roughly as follows:

1.   WATER CONTROL

Drainage and sophisticated irrigation are needed to rehabilitate salted areas, and soil mounding or shaping to enable gardening in salted lands (as explained in Module 10 Unit 2 on arid lands).

We need to rely much more on annual rainfall and water harvest than on groundwaters. Drought is only a problem where poor (or no) water storage has been developed, where tree crops have been sacrificed for fodder or fuel, and where grain crops are dependent on annual rains.

Although many sands and deeply weathered soils are free-draining,  waterlogging can occur wherever soil water lies over an impermeable soil layer or where water backs up behind a clay or rock barrier; anaerobic soil results.

 

Remedies lie in any of three techniques:

Raisesd garden beds: paths are dug down for drains, and beds raised; in very wet areas give paths a 1:500slope to prevent erosion. Figure 8.10.A

Pup open drains every 10-80 m (clay-sands) upslope and downslope or on either side of garden beds. Figure 8.10.B

Underground  pipes (tile drains; fluted  plastic pipes are best) laid in 1.5 m deep trenches and backfilled at 1.5 m (4.5 feet) deep and from 10 – 80 m (32 – 262 feet) apart, starting on a drain or stream and with a gentle fall (1:1000-1:600) to the ridge. Figure 8.10.C

 

Water retention in soil is now greatly aided by long-term soil additives. These are gels which absorb and release water over many cycles of rain. This is a pactical system only for gardens or high-value tree crop (where the cost amortises).

 

2.   SOIL CONDITIONING

Compacted, collapsed, and eroded soils need rehabilitative aeration, and a change in land use.

 

3.   FERTILISATION
 
We can reduce and replace past wasteful or polluting fertilization by sensible light trace element adjustment via foliage sprays if undisturbed soil systems and permanent crop have been developed.
 
Foliar spray of very small amounts of key elements greatly assists plant establishment, as does seed pelleting using key elements deficient in plants locally.

 
We may then be able to utilize much of the phosphate that is locked up in days, and using legumes, create sufficient nitrogen for food crops from sophisticated interplant and green manures.

4.   CROP AND PLANT SPECIES SELECTION

Many older varieties of both annual and perennial crops will yield with less fertilizer and water applications than will more recently developed varieties.

There is a growing trend amongst farmers and gardeners to preserve and cultivate these varieties not only for the reasons above, but also for flavor.

Many older apple varieties, such as some of the Pippin and Russet types, are more flavorful than, say, the market-variety Red Delicious. There is still a large diversity of food crops left in the world; the key is to grow them and to develop a regional demand.

 

Many older apple or wheat species are not only pest resistant, but have higher nutritive value, and can produce well in less than optimum conditions.

There are different species of plants that can live in almost any type of soil, starting the process back to rehabilitation. It is often the case that so-called noxious weeds will colonize eroded landscapes, beginning a slow march towards stabilization; these can be used as mulches.

 

Soils can be created or rehabilitated by these basic methods:

Building a soil (at garden scale);

Mechanical conditioning; and

Life form management (plants and macro- or micro-fauna).

 

BUILDING A SOIL

Gardeners normally build soil by a combination of three processes:

1.  Raise or lower beds (shape the earth) to facilitate watering or drainage, and sometimes carefully level the bed surface;

2.  Mix compost or humus materials in the soil, and also supply clay, sand, or nutrients to bring it to balance; and

3.  Mulch to reduce water loss and sun effect, or erosion.

 

Gardeners can, by these methods, create soils anywhere. Accessory systems involve growing such compost materials as hedgerow, herbs, or soft-leaf plots, or as plantation within or around the garden, and by using a combination of trellis, shadecloth (or palm fronds), glass-house, and trickle irrigation to assist specific crops, and to regulate wind, light, or heat effect.

By observing plant health, gardeners can then adjust the system for healthy food production.

Many gardeners keep small livestock, or buy manures, for this reason.

 

Large-scale systems (small farms) cannot be treated in the above way unless they are producing high ­value product.

Normally, farmers create soils by broad scale drainage or by soil “conditioning“. As most degraded soils are compacted, eroded, or waterlogged, they need primary aeration (by one of the many available modern machines, or by biological agents), then careful plant and livestock management to keep the soil open and provided with humus.

 

Daikon radish, tree or shrub legumes, earthworms, root associates for plants (rhizobia) all aerate, supply soil nutrient, or build soil by leaf fall and root action.

The management of livestock for least compaction and over-grazing is part of the skill of soil building and preservation.

Many organic farmers introduce worm species to pastures as part of their operation, and sow deep-rooted chicory, radish or comfrey for green manures.

 

SOIL TREATMENT ON COMPACTED SITES SOIL CONDITIONING

On the common degraded soils of marginal areas, we can observe compacted, eroded, lifeless soils; they are overgrazed and often invaded by flatweeds and non-forage species of plants.

They are boggy and wet in winter, and they are dry, cracked and bony in summer, having little depth.

 

The  reconstitution proceeds as follows:

At the end of winter, or in autumn after some rain, when the soil will carry a tractor, a chisel plough is pulled 5-10 cm 2-4  inches) deep over the area, either on contour parallels or on low slopes, starting in the high valley bottoms and driving slightly downhill to the ridges.

 

Unless there are absolutely no legumes or grasses already growing, no extra seed is applied. The response is increased penetration of roots, germination of seed, and a top-growth of pasture.

A chisel plough or soil conditioner is a rectangular steel frame (tool bar) towed by tractor or draught animals, to which a number of shanks are attached.

These are narrow -edge (axe-edged) forward-curved vertical fiat bars to the point of which a slip-on steel shoe is attached.

The shanks clamp to the tool-bar frame, and  the points  to the shank, even one implement of 5 shanks (25-50 b.h.p. tractor) covers a lot of country.

There are now at least six or seven makers of soil-loosening machines, in the USA, Europe, and Australia.

 

Geoll Wallace has produced a soil conditioner of great effectiveness. A circular coulter slits the ground, which must be neither too dry nor too wet, and the slit is followed by a steel shoe which opens the ground up to form an air pocket without turning the soil over.

Seed can be dropped in thin furrows, and beans or corn seeded in this way grow through the existing grass. No fertilizer or top-dressing is needed, only the beneficial effect of entrapped air beneath the earth, and the follow-up work of soil life and plant roots on the re-opened soil.

 

This new growth is then hard-grazed, or cut and left to lie. The plants, shocked, lose most of their root mass and seal their wounds.

The dead roots add compost to the soil, as does the cut foliage or animal droppings, giving food to the soil bacteria and earthworms, and softening the surface.

As soon as the grazing or cutting is finished, chisel again at 23-30 cm (9-12 inches), on the same pattern as before, graze or cut again, chisel again at 23-30 cm, graze or cut.

During this process, often a matter of a one-year cycle, the pasture thickens, weeds are swamped with grasses and legumes, myriad roots have died and added humus, and thousands of subsurface tunnels lead from valley to ridge, so that all water flows down into the soil and out to the ridges.

Earthworms breed in the green manure, bacteria multiply, and both add manures and tunnels to the soil.

 

A 23 cm (9 inch) blanket of aerated and living soil covers the earth.

Dust, deep roots, rain, and the bodies of soil organisms all add essential nutrients. The composted soil is, in essence, an enormous sponge which retains air and water, and it only needs a watchful eye and an occasional chiselling in pasture (or a forest to be planted) to maintain this condition.

 

If tree seed, soybeans, millet or other crop is to be planted, the sequence is as follows:

After a few hard grazings or mowings, a seed box is mounted on the chisel plough frame, and the seed placed in the chisel furrow; the grazing or mowing follows germination of the seed.

 

These new plants (sunflowers, millet, melons) grow faster than the shocked pasture, and can be let go, headed, or combine-harvested before the grasses recover.

There is never any bare cultivation, and grain growers can move to a minimum tillage method of cropping, with fallows of pasture between crops.

Soil temperature is greatly modified, as is soil water retention.

Geoff Wallace (pers.comm.) recorded as much as 13C (25F) increase on treated versus untreated soils in autumn.

 

This increased temperature is generated both by the biological activity of the soil and the air pockets left by the chisel-points at various depths, and enables earlier and more frost-sensitive crops to be grown.

Nodulation (of nitrogen-fixing bacteria) is greatly increased, as is the breakdown of subsoil and rock particles by carbonic acid and the humic acids of root decay.

Methane generated from decay aids seed germination, and water (even in downpours) freely passes into, not off, the soil.

After a year or so, vehicles can be taken on the previously boggy country without sinking in.

Drought effects are greatly reduced by soil water storage.

Water, filtered through soil and living roots, runs clear into dams and rivers, and trees make greatly increased growth due to the combined factors of increased warmth, water, root run, and deep nutrients.

Fukuoka (in japan) uses radish and Acacia; Africans use Acacia albida or Glyricidia; New Guineans use Casuarina; and Mediterranean famers use Tamarix for biological “chisel ploughs” where land is too steep and stony for implements.

Otherwise the “graze or cut and let lie” method is still followed.

On such difficult terrain as boulder fields, dunes, steep slopes, and laterites, forests of mixed legume/non-legume crops (citrus, olive,  pine, oak) are the best permanent solution to soil conservation.

No matter how we aerate soil (or condition it), whether with humble implements like a garden fork levered slightly, by planting a daikon radish, or by sheer mechanical power, we can soon lose the advantage of looseness and penetrability by over stocking, cropping, heavy traffic, or heavy-hooved animals stocked in wet weather.

 

All of these pug or compress the soil into a solid state again. Final solutions lie only in following on with permanent and deep-rooted plants (forests or prairies), and by maintaining good management (minimum tillage) cropping.

Any reduction in cultivation saves energy and soils, and wherever no-tillage systems can be devised, and heavy hoofed animals kept to a minimum, soil structure can be repaired.

Intense fire, intense stocking, intense cropping, and intensive production all threaten soils.

Thus, mechanical soil rehabilitation can be a one-time and beneficial process or another way to waste energy every year.

It is the usages that follow on rehabilitation that are beneficial or destructive to soils in the long term.

Mechanical loosening of soils is appropriate (on the broad scale) to almost all agricultural soils that have been compacted.

Soils with coarse particles, of cinder, or dunes do not benefit from or need loosening, and very stony or boulder-soil mixtures are appropriately rehabilitated not by mechanical but by organic (root penetration) methods, as are soils on steep slopes.

Some soils (like volcanic soils with permanent pastures) may never lose structure and will maintain free internal drainage after years or centuries of grazing.

Thus, we use rehabilitative energy only where it is appropriate.

Soil conditioning can be sequential, allowing a year between treatments, or all-at-once at 20 cm or so, in order to prepare for tree crop planted immediately.

The time to use implements is also critical, and early spring or at the end of a gentle rainy period is ideal, as the soil is not then brought up to the surface as dry clods, nor collapses back as being too wet.

There is only one rule in the pattern of this sort of ploughing and that is to drive the tractor or team slightly downhill, making herring-bones of the land: the spines are the valleys and the ribs slope out and down-slope (figure  8.12).

 

The soil channels, many hundreds of them, thus become the easiest way for water to move, and it moves out from the valleys and below the surface of the soil.

Because the surface is little disturbed, roots hold against erosion even after fresh chisel ploughing, water soaks in and life processes are speeded up.

A profile of soil conditioned by this process is illustrated by Figuft 8.11.

 

There is no point in going more than 10 cm in first treatment, and to 15-23 cm in subsequent treatments.

The roots of plants, nourished by warmth and air, will then penetrate to 30 cm or 50 cm in pasture, more in forests.

For disposal of massive sewage waste-water, Yeomans recommends ripping to 90 cm or 1.5 m, using deep-rooted trees or legumes to take up wastes.

I have scarcely seen a property that would not benefit by soil conditioning as a first step before any further input.

Pasture and crop do not go out of production as they do under bare earth ploughing with conventional tools, and the life processes suffer very little interruption.

 

In small gardens, the aeration effect is obtained in two ways:

By driving in a fork and levering gently, then removing it.

 

By thick surface sheet mulch; worms do the work.

 

To summarize briefly, the results of soil rehabilitation are as follows:

Living soil: earthworms add alkaline manure and act as living plungers, sucking down air and hence nitrogen;

Friable and open soil: through which water penetrates easily as weak carbonic and humic acid, freeing soil elements for plants, and buffering pH changes;

Aerated soil: which stays warmer in winter and cooler in summer;

Absorbent soil: itself is a great water- retaining blanket, preventing run-off and rapid evaporation to the air, plant material soaks up night moisture for later use;

Dead roots: as plant and animal food, making more air spaces and tunnels in the soil, and fixing nitrogen as part of the decomposition cycle;

Easy root penetration: of new plantings, whether these are annual or perennial crops; and a permanent change in the soil, if it Is not again trodden, rolled, pounded, ploughed or chemicalized into lifelessness.

Trees, of course, act as long-term or inbuilt nutrient pumps, laying down their minerals as leaves and bark on the soil, where fungi and soil crustacea make the leaves into humus

 

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