Machines for Sweetpotatoes

by O. A. BROWN MACHINES for tilling and harvesting sweetpotatoes can be used to just as good advantage as those used for other crops if a well-organized procedure is followed. Friable soil, ridges of equal width and uniform spacing, a good stand of plants in the ridge centers, and rows that can be followed with a tractor are prerequisites for mechanical cultivation.

Equipment used for building sweetpotato ridges should be, if possible, useful in other tillage operations. Single ridges can be built quickly and easily with 12-inch disks on the cultivator of a one-row tractor. Two disks, which can be adjusted independently, placed on each side of the cultivator will build suitable ridges. The disks should be adjusted to build a broad bed at least 8 inches high. It is common practice to build the rows on 42-inch centers.

For making ridges for two-row cultivation, a tractor that can build two rows at a time is needed. A middlebuster mounted on the center line of the tractor and two 14-inch triple-gang disks to build up the outer sides of the beds make a good combination for the purpose.

Ridges should be built 2 or 3 weeks before transplanting time so that the soil will become firm and weed seeds on the surface will germinate. Heavy rains may beat down the ridges and wash loose soil into the middles, but it is necessary to recondition the ridges at transplanting time and they may be rebuilt to the desired shape just before transplanting.

Texas-type sweeps have been found satisfactory for the reconditioning operation. Two 26-inch sweeps may be used for one row and one full and two half sweeps for two rows. Adjustment of the sweeps is important, for they fix the shapes of the ridges for cultivating. Sides of the ridges have the correct slope and the sweeps are adjusted correctly when the loose soil moves up the blades and is deposited on the tops of the beds. If all the soil flows across the blades, the sweeps are running too deep or are too flat or are too close together.

The height of the beds may be gaged by a plank mounted on the rear cultivator frame of a one-row tractor or on the drawbar of a two-row tractor. The plank, measuring 8 by 2 by 24 inches, should be mounted so that its 2 by 24-inch edge is in contact with the ridge directly over its center and parallel to the axle of the tractor. It should be set to board off the bed at the proper height for transplanting. The operations of shaping the ridges, boarding them off, and putting down fertilizer may be done at one time.

A simple transplanter-consisting of a water tank (a 55-gallon drum), a water distributor with a valve for regulating the water flow, a furrow opener, and two slides for packing the plants-may be mounted on a tractor. The furrow opener should be mounted as nearly under the center line of the rear axle of the tractor as possible. Such mounting will make it easy to follow the center of the ridges in fields where the rows are curved.

The equal distribution of plants will facilitate cultivation, and a uniform stand will shade the soil and help to prevent weed growth on the tops of the beds. Weed competition is an important factor in cultivation, and any delay in planting gives the weeds an advantage. Plants should be given the best possible start; early planting and plenty of water, with the soil well-packed around the plant roots, are important in proper tillage.

The mechanical cultivation of sweetpotatoes has two objectives: Removing weeds from the rows and keeping the ridges uniformly shaped. The first cultivating can be done with 26-inch Texas-type sweeps. Adjustment of the sweeps is important, as a very small difference in angle will make the difference between good and poor cultivation. The sweeps should be run shallow, so that the soil will be pulverized and move along the blades to the tops of the beds and be deposited near the small plants. The speed of the tractor is also important.

As soon as the plants begin to put them out, the runners should be directed along the tops of the beds and not permitted to run into the middles. Spring-tooth cultivators mounted on the tractor may be used effectively for removing small weeds from the tops of the ridges and for pulling the sweetpotato vines so that the first runners are parallel with the rows. The tractor should always be driven in the same direction along the rows and at a speed to prevent breaking the vines. As the vines grow, more space should be left between the spring teeth. This method of cultivation should be continued until the tops of the beds are completely covered with vines. The sweeps should be used to cultivate the middles and to shape the sides of the ridges.

Frequent shallow cultivation is most effective. Very young weeds can be killed much easier than older ones and do not clog the cultivating equipment. It is good practice to cultivate sweetpotatoes as soon after a rain as the soil can be worked and as often between rains as is needed. Weeds should not be permitted to get a start.

Sweetpotato vines for feed are available for the cost of harvesting and processing. It is an advantage to have the vines out of the way of the digging operation. The engineering problem of designing and building a machine that will meet requirements of the average sweetpotato grower for removing sweetpotato vines for feed is being solved. In 1944 we began developing a machine for collecting sweetpotato vines for feed. A tractor-operated machine was designed and built, and had its first field trials in the summer of 1945. In a field with uniform ridges and clear of weeds, we found that vines can be harvested at the rate of one-half acre an hour; in heavy vine 10 to 20 tons can be harvested in 1 day with a light tractor.

The vine-harvesting machine has two parts: A mechanism for freeing the vines from the soil and adjacent rows, and a drum and elevator for picking them up and loading them. Two 8-inch moon coulters with two 32-inch Texas-type half sweeps free the vines from one row so that they may be lifted. A cast-iron wheel 15 inches in diameter, with a 5-inch tread, rolls just behind the sweeps and presses the vines against the top of the ridge.

The pick-up drum and elevating mechanism is attached to the drawbar of the tractor. A 12-inch drum with four sets of disappearing fingers picks up the vines from the ridges and delivers them to the elevator, which carries them high enough to be loaded onto a trailer.

Sweetpotatoes may be plowed out with a turning plow, a middlebuster, or a potato digger. In preliminary tests, the broad-based bottom plow (16-inch) has shown the least damage to the sweetpotatoes. The Irish-potato digger, however, has the advantage of bringing all the roots to the surface. Less time is then required to pick them up.

Removing the vines from the rows makes digging operations easier with any method but it is especially beneficial when the potato digger is used. The throat does not clog, and there are no vines to hold the roots while they are being bruised by the moving chain or to hairpin around the blade at the ends of the rows. If the moisture condition is right, the sweetpotatoes will ride up the digger chain cushioned by a layer of soil and will fall onto a pulverized bed. More experimenting is being done with digging and handling methods to determine the injury caused by each method. Our data are not conclusive, but there are factors that are in favor of the potato digger for handling a large crop.

THE AUTHOR O. A. Brown, an agricultural engineer in the Bureau of Plant Industry, Soils, and Agricultural Engineering, has specialized in the improvement of the castor-bean, peanut, and tung nut hulling machines, and the peanut digging machine. Dr. Brown holds degrees from West Virginia University and Iowa State College.