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 cultivators, spading machines. Secondary tillage implements used include disk harrows, rotary cultivators, 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.
The moldboard plow cuts, breaks, loosens, and inverts the soil (See Figure 5.5). The plow body cuts, both vertically and horizontally, a slice of soil whose height and width are in the ratio of about 1:1.5 to 1:1. The slice of soil is lifted, moved upwards along the moldboard and turned over an angle of 120 to 150 degrees, depending on the height to width ratio of the slice. The lifting, compacting, bending and turning process causes the slice to rupture both along its length and laterally.
Chisel plows are used for loosening the soil without inverting it, thus leaving residues on the soil surface (See Figure 5.6). 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. Chisel tines cut vertically through the soil forcing the soil to move up along the curve of the tine, which flexes and breaks the soil.
The disk (disc) plow is a heavy implement, made up of 2 to 12 disks, designed for deep primary tillage and the disks are designed to throw the soil in only one direction at a time (See Figure 5.7). The resultant side force is counteracted by a furrow wheel. Disk harrows range from heavy to light implements and are used for shallow primary tillage or secondary tillage. They are equipped with rows of disks that throw the soil in opposite directions. The disk is rotated by the soil forces acting on the disk and it tears, lifts, rolls, loosens, mixes and partially inverts the furrow slice.
Disk harrows differ from disc plows in that they consist of two or more rows, or gangs, of disks (See Figure 5.8). The disks operate at an angle to the direction of travel, which imparts a cutting and turning action to the soil. The disks on the different gangs turn the soil in the opposite direction, so that the side forces are cancelled out, and hence a tail wheel is not required as in disk plows. When these gangs are arranged one behind the other they turn the soil in opposite directions and the rear disks are also staggered by half the distance between the discs, thus a smooth finish is achieved with no “ridge and furrow” effect.
Rotary cultivators, also called rotary tillers, are used for primary and secondary tillage (See Figure 5.9). Rotary cultivators have blades anchored on rotors that are bolted to a single, horizontal power shaft. These cultivators can be equipped with either conventional “C” or “L” tines, or with straight blades that are less prone to smearing the subsoil. Rotary cultivators 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 cultivators on the market use a forward rotation to mix the soil, newer reverse-tine cultivator use reverse action to pull the cultivator 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 5.10). 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 5.11). 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 5.12). 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. Heavy duty-wheeled spring-tooth harrows are known as field conditioners.
Rotary harrows are relatively new tools to fluff up crop residue, bust clods, pulverize soil, lift up weeds, and dry out soil (See Figure 5.13). They can be used for secondary tillage. The main advantages of the rotary harrow include the following; good mulching action on light to medium heavy soils; no smearing due to its tearing effect on the soil; it leaves a coarse surface; versatility; simplicity; and low cost.
Packers prepare the seedbed for planting. Packers consist of rollers made up with wheels with various types of open edges. Packers are used to finish preparing the seedbed by thoroughly pulverizing and firming the loose soil so that there will be no large air spaces or pockets.
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