Several tools have been invented to cultivate 5 to 12 cm from the crop. To avoid root damage, typical working depth for near-row tools is shallow: 2 to 5 cm. Furthermore, when working close to the crop, soil must flow either parallel with, or away from, the row to avoid burying small crop plants. Basket weeders and brush weeders can work closer to the row than disk hillers and spyders because their rotation is parallel to the row and thus the leading edge is no closer to the row than is the point of contact with the soil.
Vegetable knives (beet knives) are L-shaped knives with a low pitch so that soil movement is minimal. For early cultivations, the vertical portion of the knife is run close to the row and the tip points toward the inter-row. At later cultivations, the tip is reversed so that the surface soil can be cultivated under the crop canopy.
Disk hillers and spyders are optional equipment on shovel and rolling cultivators. They mount in the front-most position, next to the row. Early in crop growth they are set to cut soil and weeds away from the row; later they may be used to hill up soil around the base of the crop. Disks are sharp, aggressive tools that can dig out large annual weeds and cut the stems of rank perennials. They also perform well in heavy crop residue. Spyders are star-shaped wheels (Figure 4.12) that dig rather than cut the soil. They are smaller diameter (32
cm) than most disk hillers, and this allows them to work closer to some crops. Also, when cutting soil away from the row, they leave a loose soil layer next to the row rather than a smooth shoulder, and this probably reduces soil drying rather than encouraging it.
Basket weeders consist of two sets of rotating wire cages. The forward cages are ground driven; the rear cages are driven by a chain connected to the forward cages, and turn twice as fast. Penetration is shallow, 2 to 5 cm, but the soil is thoroughly worked. Consequently, few small weeds escape substantial damage even if they are not completely uprooted. The implement is unsuited to stony ground because rocks bend the baskets out of shape and can become caught between adjacent wires.
Two types of brush weeders are currently in use. One consists of powertake-off driven polypropylene brushes on a horizontal shaft; these work parallel to the crop row (Figure 4.13). They uproot small weeds, and shear off larger ones (Pedersen, 1990). The soil flow is primarily parallel to the row, which, in conjunction with narrow tunnel shields (6 to 20 cm wide), allows cultivation very close to small crop plants. Another type of cultivator is required once the crop plants grow too large to move easily through the shields. A second type uses pairs of unshielded brushes on rotating vertical shafts. Melander (1997,1998) used this type to control weeds within 1.5 cm of onion rows without damaging the crop. Fogelberg & Dock Gustavsson (1998, 1999) showed that a vertical-axis brush weeder could be used for in-row weeding of young carrots because the weeds were more prone to uprooting than carrots when both were in the two-to-four leaf stage. Brush weeders resist clogging with large weeds and debris (Geier & Vogtmann, 1987), and
may work in wet soils (Weber, 1994). An additional advantage is that, like basket weeders, they leave a loose, uniform soil surface that is not conducive to weed germination. Horizontal-axis brush weeders require a flat seedbed for consistent depth of operation (Geier & Vogtmann, 1987).
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