Richard L. Parish | 2/24/2005 10:06:30 PM
Vacuum seeders are popular among larger commercial vegetable growers. They do a good job of singulating most vegetable seeds. They are especially useful for singulating the oddly shaped seeds that cause problems for most other types of seeders.
How They Work
Vacuum seeders (Figure 1) have vertical plates with holes. The number of holes determines the seeding rate. The holes must be smaller than the seeds to be metered. The seeder has a blower that draws a vacuum on the side of the plate opposite the seed hopper. When the plate rotates through the seed hopper, atmospheric pressure holds seeds against the holes and allows the rotating plate to pick up seeds. If the holes are the right size and the knock-off mechanism is adjusted correctly, one seed will be picked up by each hole. As the plate rotates around past the seed tube, the vacuum is broken, allowing the seeds to drop down to the seed furrow.
So-called air planters use the same basic principle except that the seed hopper is pressurized rather than pulling a vacuum on the other side of the plate. With air planters, a stream of air is sometimes used to carry the seeds to the furrow from a central metering unit; vacuum seeders usually have a metering unit on each row.
The primary advantage of a vacuum seeder is the ability to singulate oddly shaped seeds. Even seeds such as squash, cucumber and melon can be fairly well singulated by a good vacuum seeder. Singulation with spherical (round) seed is nearly 100%. Vacuum seeders are much more forgiving of hole size than plate or belt seeders. A range of seed sizes can be metered successfully with each hole size, minimizing the number of plates that must be stocked by a grower.
Although vacuum seeders tend to singulate most seeds effectively, they do not always maintain the uniform spacing delivered by the seed plate. Many vacuum seeders release the seeds well above the seed furrow. By the time the seeds fall to the bottom of the furrow, the uniform spacing is gone. Although the average spacing will still be correct, the actual spacings between seeds can be quite variable. Several years of testing by the LSU AgCenter has shown that belt seeders deliver better seed spacing uniformity than vacuum seeders as long as the seeds are relatively spherical.
Power and Row Options
Vacuum seeders are available in many sizes and row configurations (Figure 2). Some are intended for small seeds and some for large seeds. Some use a PTO-powered blower and some use a hydraulic pump. Some small units even use a shop vacuum powered by the tractor’s electrical system, and one company offers a battery-powered unit.
Single or Multiple Lines
Although vacuum seeders basically deposit one line of seeds down a row, it is possible to drop seed in two or three lines per opener or scattered in a 2- to 3-inch-wide band. Multiple lines are achieved by plates with multiple rows of holes dropping seeds into separate lines. Scattered rows are achieved by metering one line of seeds and then dropping them onto a series of scatter pins in a wide opener (Figure 3). Either configuration can allow higher plant populations without overcrowding in crops such as mustard, turnip, onion, spinach and carrot.
There are several covering options available depending on seed size (and thus planting depth) and soil type. Light and heavy drag bars can be used for smaller seeds and/or lighter soils. Knife coverers can be used for deeper furrows and/or heavier soils. Press wheels may be flat, split, concave or made of expanded metal to suit different soil types and crusting conditions.
In summary, vacuum seeders are popular for precision seeding. Their forte is singulating oddly shaped seeds. They can also plant spherical seeds, but the seed uniformity will generally not be as good as with a belt seeder.Vacuum Seeders for Commercial Vegetable Crops