Soil Tillage in Organic Farming Systems
Soil Tillage Implements
Tillage implements are important components of both soil and weed management systems in organic farming. Some of the implements used for primary tillage include moldboard plows, disk plows and tillers, heavy disk harrows, chisel plows, rotary tillers, spading machines. Secondary tillage implements used include disk harrows, cultivators, rotary tillers, spike-, spring-, and tine-toothed harrows, and packers. The following section discusses the role of tillage tools in soil management, including managing crop residue, terminating cover crops, preparing a seedbed, managing soil compaction, and weed control.
Moldboard plows are designed to bury plant residue as well as loosen the soil (See Figure 6.5). The soil-working actions of the moldboard plow are slice, lift, fracture, and invert. Moldboard plows can be run at different depths and may be used to completely or incompletely turn the plow furrow. By adjustment, they can flip a furrow slice 180 degrees such that the soil surface is inverted. Moldboard plows are used when the soil is sufficiently moist to allow the plow to pass through easily but not so wet as to cause the furrow slice to stick to the face of the moldboard.
Moldboard Plow Configurations
Moldboard plows come in various shapes and sizes, which determine the depth of the plow and how it moves the soil. The essential parts of the moldboard plow are the share, which cuts the furrow slice from the soil matrix, the shin and moldboard, which turn and shatter the soil, and the landside, which is located behind the moldboard to deflect sideward pull of the tool. The moldboard and landside are attached to a frog. There are different types of bottom designs suited to different speeds of operation and types of soil—general purpose bottom, high-speed bottom, slatted, stubble bottom, reversible bottom, and semi-deep bottom. The high-speed moldboard has less curvature at the upper end than the general purpose bottom. Slatted bottoms are used in heavy, sticky soil—50 percent of the bottom is removed, resulting in better flow of soil and less friction. The stubble bottom is an abruptly curved moldboard, which quickly turns the furrow slice.
Chisel plows are used for loosening the soil without inverting it, thus leaving residues on the soil surface (See Figure 6.6). Chisel plows generally provide results similar to those of the moldboard plow but require less energy and leave significantly more residue on the surface. Chisels also allow for more flexibility in the depth of tillage, generally from 5 to 12 inches (13 to 30 cm), with some tools specifically designed to go deeper. The chisel plow is easy to operate and helps to loosen the soil to enable operation of conventional planting equipment.
Chisel Plow Configurations
Chisel plows can be wheel-mounted pull-hitch types or three-point hitch-mounted types. Chisel plows come with curved shanks. Springs on these shanks determine how well the chisels penetrate soil (especially if soil is compacted). A variety of points can be mounted on the chisel shanks. These points can be wide or narrow, as well as twisted or straight. The wider and more twisted the point, the more soil disturbance will be achieved by the chisel plow and the more residue will be covered.
Disk plows can be used for both primary and secondary tillage (See Figure 6.7). They consist of a series of disks mounted on a frame. Disk plows come in a heavy version, as a primary tillage tool that usually goes six to eight inches (15 to 20 cm) deep, or a light version, as a secondary tillage tool that performs shallower tillage and leaves residue on the surface. Heavy disks can be used for primary tillage, and adding additional weight to the disk can help it cut farther and incorporate crop residue better.
Disk Plow Configurations
Disk plows come in many different types, such as wheel mounted pull hitch or three-point hitch types, one-way as well as two-way disk plows. They come in several different shapes and sizes and can be arranged in different rows and at different angles. Disks can be spherical or cone shaped. Spherical disks are less aggressive and pack soil more but tend to plug less under certain sticky soil conditions than cone-shaped disks. Disks come in many different sizes and can have a smooth or notched edge. Small blades penetrate soil better than large blades due to their smaller contact area with the soil.
Disk harrows are implements that stir and level the soil, break up clods and destroy weeds by mechanically loosening them or burying them (See Figure 6.8). Disk harrows accomplish this through the use of concave disk blades with sharp edges. Disk blades are mounted on common shafts to form gangs. Adjustment of gang angle controls cutting aggressiveness. In operation, the gangs are pulled at an angle to the direction of travel with the concave side of the disks slightly ahead of the convex side. While the basic action has a loosening effect on top layers of soil some compaction results below the top layer. Disk harrows also are useful in cutting up crop residue when the quantities are not too excessive. For instance, they are often used to cut up corn stalk residues prior to plowing.
Disk Harrow Configurations
Single-action disk harrows consist of two gangs of disk blades placed end-to-end to move soil in opposite directions. Most single action disk harrows are arranged with the concave sides of the disks facing outward. Thus, they tend to move soil toward the outside of the strip being tilled and tend to leave an open furrow at the center. Double-action disk harrows often referred to as tandem disk harrows have a second pair of gangs following the front gangs
Rotary tillers are used for primary and secondary tillage (See Figure 6.9). Rotary tillers have blades anchored on rotors that are bolted to a single, horizontal power shaft. These tillers can be equipped with either conventional “C” or “L” tines, or with straight blades that are less prone to smearing the subsoil. Rotary tillers can be adjusted for ground speed and rotational velocity to either pulverize the soil or leave it rough and cloddy to slow erosion in winter. While most tillers on the market use a forward rotation to mix the soil, newer reverse-tine tillers use reverse action to pull the tiller into the ground by burying larger soil clods underneath smaller clods, often leaving a finer seedbed with less compaction.
Spading machines are an alternative to using a rotary tiller (See Figure 6.10). Spaders are either rotary or reciprocating, and the spades on both types move more slowly than a rotary tiller through the soil. Spading machines work the soil more effectively without causing compaction.
A field cultivator is an implement used to perform secondary tillage operations such as seedbed preparation and weed eradication (See Figure 6.11). Field cultivators are equipped with steel shanks that are typically spring mounted to permit the shank to move within the soil and shatter clods. The springs are recommended on each shank in soil with obstructions such as rocks or tree roots.
Spike-, Spring-, and Tine-Toothed Harrows
Harrows are effective in breaking remaining soil crusts and clods from primary tillage, smoothing and firming the soil surface, aerating the soil, and pulling emerging weeds. Three types of harrows typically are used in secondary tillage: spike-, spring-, and tine-toothed. Spike-tooth harrows have rigid spikes that often are mounted on an angle to flow over residue (See Figure 6.12). They are more aggressive than tine-tooth harrows and will bust up crust and clods and smooth the soil. The spring-tooth harrow is more aggressive than the spike-tooth harrow, but it tends to rake up any surface residue of significant size, so it is not suitable for conservation tillage.
Rotary harrows are relatively new tools to fluff up crop residue, bust clods, pulverize soil, lift up weeds, and dry out soil (See Figure 6.14).
Packers prepare the seedbed for planting. Packers consist of rollers made up with wheels with various types of open edges. Rollers are continuous with no open areas and are used to break up clods on the surface. Another use is to finish preparing the seedbed by thoroughly pulverizing and firming the loose soil so that there will be no large air spaces or pockets. Packers press the upper soil against the subsoil making a more continuous bed in which moisture may move to the seeds and ultimately the roots.
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