| | Figure 1. Belt seeder metering unit showing belt, base and choke |
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| | Figure 2. Belts for belt seeder to deliver one, two or three lines of seed |
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| | Figure 3. Bases for use with seeds of different sizes. |
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Many years of testing at the LSU AgCenter have demonstrated that precision belt seeders deliver the best seed spacing uniformity of any type of vegetable seeder – if the seeds are spherical (round) or nearly so. The principles of operation of a belt seeder are simple. Belt seeders are versatile and can meter a wide range of seed types and sizes.
How Belt Seeders Work
Belt seeders use a rubber belt with holes to pick up individual seeds and carry them back to a drop point (Figure 1). The belt passes under a small seed chamber fed by the main seed hopper. Individual seeds fall into the holes in the belt and are then carried to the rear edge of the base where they are released. A wheel at the rear edge of the base helps force the seeds out of the belt holes.
Adjustment for Seed Size
Several components must be properly selected to meter seeds of a given size properly. The most obvious component is the size of the holes in the belt (Figure 2). The holes must be large enough to allow the seeds to fall in easily, but small enough to avoid not just doubles but attempted doubles wherein two or more seeds fall partially into the hole, bridge across the hole and cause binding or a skip. Belt thickness can vary. Standard thickness rubber belts are used for most crops, but thin plastic belts can be used for very small seeds such as carrot.
The spacing of the holes (number of holes per belt) determines the seed spacing, although this can be modified somewhat on the machine by using stepped sheaves to vary the drive ratio and thus seed spacing. Belts are also available with ribs on the outside to carry seeds with a diameter greater than the thickness of the belt. These ribbed belts must be used with grooved bases (Figure 3). The larger the seed size, the larger the groove must be. Smooth bases are used with small seeds. A final component that must be adjusted for seed size is the choke plate that controls flow into the small seed chamber from the main seed hopper. Larger seed sizes require a smaller choke plate and thus a larger opening.
Multiple Lines of Seed
It is possible to drop seeds in one, two or three lines per row using belts with one, two or three lines of holes (Figure 2). These belts are paired up with one, two or three line openers (see article on Openers, Coverers and Presswheels). These multiple line configurations are good for crops such as onion, carrot, mustard, turnip and spinach. Multiple lines per row allow higher plant populations of these crops without crowding.
Seeding Quality
Uniformity of seeding can be excellent with a properly set up seeder and spherical seeds. Other seeders such as some vacuum seeders can do a good job of metering individual seeds but often don’t maintain that uniform seed spacing in the seed furrow. The feature of the belt seeder that allows good seed spacing uniformity is the low drop point. Seeds are released from the belt on a Stanhay S870 seeder at about 1 inch above the bottom of the seed furrow since the metering unit mounts right down in the opener. On many other seeders, including most vacuum seeders, the seeds are released several inches above the seed furrow (7 inches above the seed furrow on a Gaspardo SV255 vacuum seeder). By the time the seeds have fallen several inches, the uniform spacing has been lost.
Odd-Shaped Seeds
Belt seeders will not reliably singulate oddly shaped seeds such as cucumber, squash, carrot or melon. These crops can be planted successfully with a belt seeder, but doubles and multiples (as well as some skips) will result. Many acres of these crops have been successfully planted with belt seeders, but you will not get the singulation and uniform seed spacing with oddly shaped seeds that you get with spherical seeds. Vacuum seeders do a better job of singulating oddly shaped seeds.
Operating Speed
Belt seeders have to be operated slowly. If your ground speed is too fast, the belts will turn too fast and not pick up seeds. Depending on the belt drive ratio you are using, your speed should be limited to 1.5 – 3.5 mph. See your operator’s manual for a table of speeds at different drive ratios. The slower you go, the better your results will be.
Tricks to Make a Belt Seeder Work Better
After the holes are punched in a seed belt, there will be fuzz around the hole because of the fibers in the belt. Passing a torch quickly over the fiber side of the belt will burn off that fuzz and leave a clean hole that won’t trap seeds. Be careful not to overdo the flame. You want just enough flame to cause the fuzz to glow red and burn. If your belts slip in use, first be sure the side of the housing is not pressing too tightly. You may have to add a small flat washer under the plate. Also clean the interior, including the wheels, thoroughly. A light dose of clear belt dressing applied to the cleaned drive wheel can help, too. Electronic monitors are available to be sure the belts keep turning.
In summary, a belt seeder offers the best precision in seed spacing available (for spherical seeds) – if properly set up.