The harvesting of peanuts is generally a three stage operation: (1) the tap root is cut and the soil loosened around the peanuts; (2) the vines and nuts are lifted from the soil, passed over a shaker to shake off loose soil, and collected in windrows; and (3) the windrows of peanuts and vines are picked up and passed through a picker or thresher to separate the nuts from the vines.
Stage 1 and 2 are usually done as a single operation, as equipment to dig and shake the vines is operated by the same tractor. The vines are left in the windrow from 3 to 10 days before stage 3, or threshing, is done. Peanuts have been dug and threshed in a single operation, but it required longer to dry the nuts and the quality was below standard.
The peanut plant has a central tap root. Some varieties have vines or runners radiating out 8 to 12 in (20.3 to 30.5 cm) from the tap root, and there may be nuts under the entire plant. Other varieties don’t have runner vines, and the nuts are bunched on fibrous roots near the tap root.
Digging of peanuts requires a long knife set fairly flat with the cutting edge extending backward at an angle of about 30o. the knife is set to run about 5.1 cm deep underneath the plants to cut the tap roots and loosen the soil around the nuts. The knives for digging two rows are usually mounted centrally on the tractor. Some grower use two long-bladed cultivator half-sweeps mounted on a cultivator frame to dig peanuts. The knives and sweeps blades are set so that they extend toward each other to aid in partially windrowing the vines. Rods can be attached to the knives and knife standards to aid in windrowing the vines from the two rows.
Peanuts for combine or stationary threshing should be as free of dirt as possible. For combine threshing, four to six rows are windrowed together. The side-delivery hay rake has been extensively used to windrow and shake peanuts. This type of work is heavy for a slide-delivery rake and causes excessive wear and breakage of parts. The peanut vines are tangled, and the windrow is too compact for rapid drying.
Special equipment has been developed which lifts, shakes, and pieces the vines in relatively light and untangled windrows. There are a number of machines available for lifting and shaking peanuts.
Peanut threshers and pickers
There are generally two types of machines for separating the peanuts from the vines. They are classified according to the type of teeth used on the cylinder and are termed threshers and pickers. The thresher has the regular straight teeth similar to those used on a grain thresher, except that they are spaced farther apart on the cylinder and concave bars. The picker has spring teeth on both the cylinder and concave bars.