THE DEVELOPMENT OF THE MODERN SUB-SOIL PLOW – Allan Yeomans
The basic principles used in Keyline of increasing the fertility of soils has not changed since they were first described in my father, P.A Yeomans’ book, The Keyline Plan, published in 1954. What has changed is my designs of the cultivating equipment and the modification of the techniques for soil building that the newer designs have permitted.
The production of fertile soil from biologically inactive subsoil is not difficult and one technique is well known. We know that if sufficient quantities of dead vegetation and animal manures are available for composting, and the composted materials are blended into inert subsoils, rapid fertility can occur.
For broadacre farming however, there is never sufficient waste materials available. The soil and the soil life must be managed to produce its own composting material. Keyline techniques do just that and do it extremely well.
The Keyline processes for the enrichment of soil were actually well developed before suitable implements were found that would handle the job. Earth moving rippers were often used because of my father’s familiarity with such equipment. Results with this equipment were sometimes spectacular, sometimes disastrous. Rapid changes and improvements in soil fertility levels were, however, being achieved with ever increasing success. At that time a Graeme Hoeme Chisel plow was imported into the country by a long time friend. This design looked very promising and the implement was tried out. It worked well and was commercially available.
In June of 1952 my father and I were in the United States on another matter. While there, we called in at Louis Bromfield’s well documented “Malabar Farm”. The techniques of Keyline had, in my opinion, progressed well ahead of what was being done by Bromfield.
In Amarillo Texas we met Bill Graeme of the Graeme Hoeme Chisel Plow Co. A deal was struck where by we made the plow under their patent in Australia. The words and the concept “chisel plow” were unknown in Australia in 1952. The patent was found to be unenforceable in this country and so anybody could copy the designs. This inevitably occurred as Keyline ideas spread, so we were forced to go our own way. The plow was strengthened considerably until it “could go any where the farmer was game to take his tractor”. That was my father’s design requirements and consequentially, mine too.
Keyline soil building techniques were then slightly restricted by the limitations imposed by the plow itself and these are the techniques described in the Keyline books.
The plow business was sold in April 1964, with a proviso that P. A. Yeomans, and myself as the design engineer, had to keep out of the agricultural machinery business for a minimum of five years. The designs for a deep working, low disturbance chisel plow with the strength characteristics of earth moving rippers, a “sub soiler chisel plow” were moth balled.
They re-emerged, after this enforced hibernation, as the “Bunyip Slipper Imp” with “Shakaerator”. This implement won the Prince Phillip Award for Australian Design in 1974.
The plow has an extremely strong, solid, rigid frame. The tynes or shanks are made from cast tool steel. They are narrow with a tapered leading edge. They travel through the soil with very little resistance, like a sail boats fin. The separate digging point is shaped like a long flat arrow head, tapering out to about 4″ (100 mm) wide at the rear. The digging angle is very flat, only 8 degrees. A vertical “splitter fin” is incorporated on the top face, and becomes a vertical blade to the arrow head. In use, and in deep cultivation, the splitter fin initiates a vertical crack through the soil above, up to the surface. The side blades lift and loosen the earth between the shanks, and then allow it to re-settle.
No mixing occurs between soil profiles and root disturbance is insignificant and gentle. After cultivation, the ground surface often appears as if undisturbed, yet is strangely spongy to walk on.
The Shakaerator is an off set heavy fly wheel, bolted to the plow frame, that assists soil shattering and reduces tractor horse power requirements in most soil types.
By then I had my own independent engineering business, and by constraint, not in agriculture. This was where the new plow prototypes were built. After my father’s death in 1984, my company took over the complete manufacture of the plow. Improvements continued and six new patents have subsequently been issued. Three of which have won implement design awards at the Australian National Field Days.
The rapid soil building processes of Keyline were no longer restricted by the use of chisel plows, and the techniques were streamlined.
In addition, the use of this new plow enables the soil to absorb high quantities of run off from storms, and heavy downpores. This is the runoff that normally fills dams, and can often cause erosion. These effects have be catered for in the design of whole farm layouts. Greater emphasis is now placed on the location and size of the first dam constructed. This first dam now tends to be of greater capacity than previous designs called for. Fewer and larger farm dams now prove to be economically more viable. This first dam is sized and placed to so enhance the returns to the farm, that future dams can become self financing by the farm itself. My brother Ken has developed computer simulation design techniques by which such decisions can be idealised. Design errors are virtually eliminated in the process, and financial and ecological viability can be assured.
The Keyline soil building process is now much more rapid with the use of this plow. Many clones of the plow have now been produced, often with interchangeable components, and if used correctly these plows can be equally effective.
The real value, almost one might say, the cash value of a soil is determined, firstly by the basic mineralisation within the soil. This is ordained by its geological history and formation. The farmer is not able to change this, outside the addition of some exotic trace elements. And the second determining factor, is the amount of humic acids within the soil, their age and their stability. The fulvic acids are here considered as subvarieties of the humic acids. If both abundant minerals and abundant humic acid is present, the soil is acknowledged as basically rich. Farming can, and does, change the content of humic acid within the soil. Most classic current farming practices in the Western World decrease the humic acid content of soils. The resulting soil deterioration manifests itself as, increasing dependency on chemical inputs, increased erosion and rising salinity levels.
To produce good crops in rich soils it is generally only necessary to maintain, within the soil, reasonable levels of biological activity.
Humic acid is not a simple acid, like hydrochloric acid or sulphuric acid. Humic acid is hardly an acid at all. When organic matter has been through all the biological processes within the soil, very large, relatively stable organic molecules are the ultimate result. Their formation is extremely haphazard and their actual chemical composition can have millions of variations. They are mildly acidic and so collectively they are described as “humic acid”. Individual molecules can contain thousands of carbon atoms. They are so big that they can be acidic on one side and alkaline a little further around the same molecule.
For the farmer they have two very important characteristics. For a plant to take up an element for its growth, it must be in an available form. However, if the elements in the soil were in soluble form, they would have long since been washed, or leached away. Something else therefor, must occur for plants to exist at all. When acids break down basic geological minerals, nutritious soluble chemical elements become available, and these, fortunately, attach themselves loosely to the highly variable outer surface of the humic acid molecules. The element is no longer soluble, but it is readily available to the tiny root structures of plants and fungi. As far as a plant is concerned, the humic acid molecule is a supermarket, and its outer surface is the richly stocked shelves.
Carbon dioxide dissolved in rainwater forms carbonic acid. This carbonic acid breaks down the fine rock particles, replenishing the shelves in the supermarket. Also, biological activity within the soil can produce tiny quantities of acids, a thousand times stronger than the carbonic acid of rain water. These acids make available to the surface of the humic acid molecule, elements that would otherwise be totally inaccessible or unavailable.
If the soil is devoid of biological activity, and the minerals in the soil have been used up by growing crops, re- mineralization of the soil can only be achieved by the much slower use of carbonic acid derived from rain water. I believe this to be a considerable, although unrecognised, justification for the “long fallow”. It takes a long fallow, or simply a long time, to re-stock the shelves in the supermarket.
When only minimum biological activity can occur, then the concept of “resting the soil”, starts to make sense.
Humic acid molecules can last thousands of years, and these were described in German literature as “Dauerhurnus” (dauer – German and endure – English). The long lived dauerhumus does not itself form part of soil biological activity. Other humic acid molecules however, do form that are much less stable.
They can last anywhere from minutes to months. These molecules can, and do, get involved in biological activity. They contain, within themselves, protein and other similar structures containing nitrogen, as also do the long lived variety. Soil biological activity breaks down the short lived molecules and release a constant, and harmless trickle of ammonia to the fine plant roots, invigorating plant growth. This is “Nahrhumus”, (nahr to nourish). Almost all of the nitrogen supplied to plants in healthy soil, is derived from this organic material within the soil.
It is well known that total soil organic matter constantly decreases with mono-cropping, and by the use of soluble chemical fertilisers, almost all of which kill earthworms and destroy microbiological soil life. The organic matter content decreases over periods, usually in excess of thirty years, and up to one hundred years, to a level of about half that in the original soil. Then a stability seems to be attained. This, it is claimed, proves that chemical agriculture does not continue to decrease soil fertility.
I tend to believe that most biological activity has already ceased, and the organic matter, still in evidence by high temperature soil testing, exists only in the form of dauerhumus. These then are the extremely stable, but now empty, supermarket shelves.
So many problems are solved simply by increasing soil’s natural fertility. And it all starts with dead plant material, air and water. Activity then starts, bacteria, fungi, actinomycetes and worms devour the dead plant material, die, and in turn devour each other. In the process, concentrated acids are produced that break down tiny rock structures, making available crucial elements in the life cycle.
Complex humic acid molecules are ultimately formed. Some are broken down by more biological activity, producing ammonia for plant growth. Around others, the soluble newly released element become attached, but still available for healthy plant growth. Long chains of sugar like chemicals, polysaccharides, food stores for bacteria, are formed that bind the soil together. The tiny root like structures of fungi bind the soil particles in the same way. Small aggregates of these soil particles and sand and clays accumulate. In our hand we feel the whole thing as good soil structure.
Pieces of the less stable humic materials reform, and reform again until ultimately, relatively stable humic acid molecules are created. As the total organic content rises, earthworms move in and establish themselves. Their casts are a rich source of humus and their slimes and glues enhance soil structure. The soils ability to retain moisture, its “field capacity”, rises dramatically and, to the farmer, rainfall patterns become less critical. This intense biological activity is the necessary “bio” in “biodegradable”. Soluble heavy metals, poisons, become attached to the humic acid molecule and are no longer in solution and a threat. They won’t be selected by the plants’ discerning fine root structures.
Food producing plants grown on such soils are healthy, mineral rich and nutritious, and extremely resistant to insect attack. Weeds and non-food producing plants cannot compete in rich soils. This is not just accidental but logically inevitable.
For this all to happen, we must first structure an ideal soil environment, and then, if we can, we should water it.
The most rapid increase in soil fertility, and soil organic content in broadacre farming, is obtained by the utilisation, and the growth manipulation, of the legumes and grasses. The current model of Yeomans Plow was designed specifically, so that its use would create this idealised environment.
If conventional chisel plows are used to an excessive depth, for subsoil aeration and rain water retention, destructive mixing of soil layers results. For this reason, chisel plow use in Keyline required a program in which cultivation was only progressively deepened. Depth of cultivation was determined by taking a spade, and checking the depth of the root structures resulting from the previous cultivation. Tine spacings were kept at 12″ (300 mm).
Because of the resultant damage to existing pastures, it was often risky, and it was not advised to cultivate when pasture grasses were in short supply, or when approaching a period of, possibly, hot dry conditions.
Using these new implements we can now recommend an initial cultivation depth of 8″ (200 mm) or more. Any less than 6″ deep the cultivating effect is similar to a chisel plow, with a typical V shaped rip mark of loose earth being formed. If a hard pan exists, and conditions are dry, large clods can still be turned up. By increasing the depth of cultivation, a point will be reached where clods are not produced at all. Horizontal fracturing spreads sideways from the plough point and surface disturbance is minimal.
Tyne spacings should be much wider than would be recommended for chisel plows. 24″ (600 mm) spacings are perfectly reasonable. 18″ to 20″ (about half a metre) would be a good general guide. If horsepower is limited, it is wiser to maintain the cultivation depth, and, if necessary, decrease the number of tynes being used. In this way little pasture damage occurs, good deep aeration has been achieved, and enormous quantities of storm rains can be absorbed before any run off occurs. Even with no following rain, very little soil moisture will be lost. In many instances plant roots will gain access to otherwise unavailable subsoil moisture.
The subsequent grass growth should be mown, or heavily grazed by overstocking to achieve the same effect. Stock should be removed promptly to permit rapid unhindered regrowth of the more nourishing pasture grasses. Subsequent cultivation should be repeated at or about the same depth. These Keyline stocking techniques are detailed elsewhere.
Within weeks of the first cultivation the decomposition of cast off root structures, following mowing or grazing, can promote soil colour changes from biological activity deep in the subsoil. This is quite impossible using a conventional chisel plow.
Cultivation, prior to cropping, using this plow at these depths invariably and dramatically increases crop yields. These dramatic increases are not always permanent. I believe that the dramatic increases result from exploiting soil layers, that have been “fallowing” for hundreds or even thousands of years.
The minerals having accumulated on clay particles, as they do on the humic acid molecules. The dramatic increase in crop yields can only be maintained, by the inclusion of grasses and legumes into the cropping programs. This is to promote biological activity, and thus maintain the supply of minerals and elements.
Again; So many problems are solved simply by increasing soil fertility.