MECHANICAL WEDGES IN NATURE INCLUDING LAND IMPRINTING
August 15, 2003
Robert M. Dixon, Ph.D
In high school physics, we learn about a very useful tool called the wedge or a double inclined plane-in other words a V-shaped object in cross section. Nature depended greatly upon V-shaped objects in the evolution of plants and animals that rely, in turn, on wedges in different ways for their survival. The list is long for nature's wedges, but those that come quickly to mind include teeth, fangs, fingernails, toenails, claws, talons, hooves, beaks, noses, tongues, snouts, stingers, horns, seeds, seedlings, roots, shoots, pollen tubes and penises. Some seeds even wedge their way into the soil to germinate into a seedling whose wedge-shaped growth points work their way into the sunlight above and into the soil moisture below-two essentials for seedling survival. Claws, talons, beaks, stingers, and horns are used for defending territory and obtaining food. Wedge-shaped teeth tear and bite food loose so that it can be chewed, swallowed and easily digested. In mammals and other vertebrates the process of insemination, and thus reproduction, relies on wedge-shaped penises to introduce sperm to the egg-the basis for much of the biodiversity found in nature. Thus, wedges play a vital role in life on earth as we know it.
Many of the tools that humans have invented are wedges in one form or another and they, like in other life forms, are used for defense or to obtain food. Primitive humans used rock knives, swords and arrowheads. These rock wedges slowly evolved into wedge-shaped steel axes, knives, swords, and bullets to acquire food and security more efficiently.
Virtually all the tools that have been invented to till the soil for food production are wedge-shaped. They literally wedge their way into the soil to loosen it, kill weeds, and prepare a seedbed for the crop to follow. In so doing, however, these wedging tools expose the soil to raindrop impact by inverting it, bleed resources by making continuous furrows, destabilize the soil by oxidizing plant litter and organic matter, all of which lead to accelerated erosion and loss of topsoil and the teeming life therein. Thus in the long run, agriculture based on the use of such wedging tillage is not sustainable.
What is needed for land sustainability is a tillage method that makes a seedbed without soil inversion, covering of surface litter and plant residues, and continuous surface furrowing that tends to bleed resources downslope rather than holding them in place for enhancing crop production indefinitely into the future for sustainability.
Such a process has already been invented and is currently under development while at the same time the technology is being transferred to users. The process is called land imprinting and the machines used for applying the process are called land imprinters.
Like other tillage implements developed heretofore, land imprinting involves a wedging action on the soil, but unlike conventional tillage implements this wedging action does not invert the soil, loosen the soil, cover plant materials, and create continuous furrows to lead resources downslope with each successive rainfall event. Instead V-shaped imprinting teeth are pushed into the soil surface wedging the soil forward, backward, and upward as the steel roller, upon which the teeth are mounted, turns. In this manner, the rolling land imprinter wedges out staggered, V-shaped depressions or seedbeds about one-foot-square in size and shape, each of which can hold up to a gallon of water and other land resources in place to enhance land productivity and sustainability.
A hand imprinter is also under development for wedging imprints spaced about one foot apart in a staggered pattern. One physically fit adult can hand imprint about one acre per day.
Perhaps the best natural form of imprinting is the hoofprinting of ungulates or the hooved mammals such as pigs, goats, cattle, horses, deer, elk, giraffes, and elephants. The best seedbed is produced by a single hoofprint. Repeated hoofprinting can lead to soil compaction and the trampling of existing vegetation. After all, hooves were designed by nature for flotation and traction to benefit the owner, not for creating seedbeds for plants. However, through long periods of co-evolution, plants became adapted to the beneficial aspects of hoofprints, especially their ability to trap land resources needed by seeds and seedlings.
Now that we've seen what land imprinters do in the wedging out of small isolated watersheds, let's go one step deeper into the basic physics/mechanics of the making of an imprint at the soil surface. It takes force, but how much, to drive the imprinting teeth into the soil surface to create these small basins for holding resources, germinating seed, establishing seedlings, and growing biomass for whatever purpose. The basic structure of the rolling land imprinter provides about 500 pounds of weight of imprinting force per foot of roller length. An additional 500 pounds per foot can be added to the imprinter frame as ballast for a maximum imprinting force of 1000 pounds per foot of roller for imprinting hard soils. This range of 500 to 1000 pounds per foot corresponds to a range of imprinting pressures of 15 to 30 psi-the same operating range as present in the tires of most farm equipment.
Back to high school physics again where students learn that the downward acting force or weight is given by the product of the pressure per unit area and the area in contact or F=PA. Thus with a constant F, P & A are inversely proportional-as P increases, A decreases and vice versa. As A approaches zero, P approaches infinity and vice versa. This simple relationship is often illustrated by comparing the foot pressure of elephants and women wearing spike heeled shoes. Because of the difference in contact area a woman's heel can break through a hardwood floor that easily supports an elephant-just as a sharply pointed nail can be driven into an oak board with a couple of blows from a light hammer.
The power of the wedge is evident in the action of the wood splitting wedge. The wedge is driven into a piece of wood until the wood fibers are pushed apart enough for splitting or structural collapse to occur. The power of the wedge was also apparent when the first rolling imprinter was fabricated at the USDA machine shop in Tombstone , AZ during which it was rolled a short distance on the concrete shop floor. Not too surprisingly, the sharp, new teeth indented the concrete floor. The contact area of the new teeth was nearly zero; therefore, the imprinting pressure was nearly infinite and something had to give, even concrete. Once the concrete was indented to raise the contact area significantly, the floor was capable of supporting the imprinter. The load-bearing capacity of the floor became equal to the load by raising the contact area from near zero to a small finite area. One final example of the power of the wedge is the stinger of a wasp that develops many tons of psi to sting its victim.
The power of the wedge can be maximized by keeping the cutting edge sharp. The teeth of rolling imprinters are sharpened automatically as they tend to hollow grind just behind the leading edges by the sand in the soil. However, the cutting edges of hand imprinters need to be sharpened periodically within an angle grinder. Keeping the cutting edges sharp minimizes the wedge-soil contact area, thereby maximizing the imprinting pressure and the ease with which imprints can be wedged into the soil surface.
Currently under development is a method for using a gang of rolling coulters to weaken a hard, dry soil's resistance to the wedging action of rolling imprinters. This development is expected to reduce the amount of tow-frame ballast needed to achieve a full-tooth imprint in hard soils. Otherwise, a soil's imprintability (wedgeability) tends to increase as soil moisture increases, sand content increases, bulk density decreases, and organic matter increases. Under no-till imprinting, organic matter tends to increase annually, thereby making the soil imprintable with less ballast.
The rolling coulter attachment being developed can be replaced by no-till drill units spaced one-foot apart when deeper placement of large seeds is desirable. Like the gang of rolling coulters, these drill units would also reduce the ballast required for obtaining a full imprint.
In conclusion the rolling coulters and drill units also have a wedging action on the soil, but with minimal disturbance. The furrows produced by the drill units are erased by the imprinting roller, which follows.