Precision seeders for vegetables:How precise are they?

Linda F. Benedict, Parish, Richard L., Bracy, Regina P.

Regina P. Bracy, Richard L. Parish and Joe McCoy

Establishing a full stand of fieldgrown plants is necessary for high yields of vegetables. Unfortunately, the grower cannot always control factors that hurt stand establishment, such as soil crusting, temperature extremes and excessive soil moisture. The grower, however, can minimize or overcome the effects of climatic and biotic factors by using the proper seeder.

Seed spacing uniformity and seed placement depth are important for an adequate and uniform stand and are directly affected by seeder performance. In several studies, researchers at the Hammond Research Station evaluated the seeding uniformity of precision vegetable seeders and the effects of seed coverers, presswheels and seeding depth on stand establishment of several vegetable crops.

Seeder uniformity

Two types of precision vegetable seeders, belt and vacuum, were evaluated for seeding uniformity with the seeds of five vegetable crops. The crops represented a range of seed shapes: spherical or nearly spherical (cabbage and onion), angular (spinach) and elongated and flat (carrot and cucumber). The seeders were operated over a board 6 inches wide and 20 feet long coated with grease to prevent seed bouncing and to retain exact placement of the seed. Seed spacings were recorded.

The belt seeder did an effective job of uniformly seeding spherical (cabbage) and nearly spherical (onion) seed. Although the vacuum seeders did a better job with elongated seed (carrot and cucumber) than the belt seeder, none of the seeders did an adequate job of spacing cucumber and carrot seed uniformly. Seeding uniformity of all seeders with spinach seed also was insufficient.

Overall, the belt seeder was the most uniform and precise of the seeders tested. Seeding uniformity of the belt seeder was good when seeding spherical and nearly spherical seed. When seeding elongated or angular seed with the belt seeder, multiple seed drops and reduced seed spacing uniformity should be expected. 

Seed coverers and presswheels

Although several types of seed covers and presswheels are available from precision seeder manufacturers, the effects of covering devices and presswheels on plant emergence of directly seeded cole crops have not been determined. Ten experiments were conducted at the station during spring and fall. Planting times and field locations were varied to assess planter component performance under different soil moisture conditions and texture.

A Stanhay belt seeder was equipped with combinations of four covering devices and four rear presswheels for a total of 16 treatments. Covering devices included standard drag (0.6-inch-square steel bar), light drag (0.4-inch-square steel bar), paired arms (0.2-inch by 1.2- inch steel paddles) and no covering device.

Presswheels included standard smooth steel banded (4.5-inch wide by 9.0-inch diameter), concave split (3.5- inch wide by 10.8-inch overall diameter with 0.5-inch space between conical wheels), flat split (4.5-inch wide by 9.0- inch diameter with 1-inch space between wheels) and cage (4.5-inch wide by 9- inch diameter covered with expanded steel mesh). All presswheels and covering devices, except the light drag, are stock parts available with the Stanhay seeder. The light drag covering device, a replica of the standard drag with a smaller drag bar, was constructed in the university’s shop. Growers would be able to replicate this.

Savannah or Florida Broadleaf mustard was planted using a single-line belt and single-line opener with a seed spacing of 2.7 inches or 3.3 inches. Asgrow XPH 5957 cabbage was planted using a single-line belt and single-line opener with a 3.3-inch seed spacing.

At the March, April, August and October planting dates, soil moisture was optimum for seeding. Soil moisture at the November planting was not conducive for optimum seed covering.

All plantings received at least 0.6 inches of precipitation within three days after planting, which is adequate moisture for germination and growth. Heavy rainfall (7.8 inches) occurred within three days of the October planting.

All the covering devices and presswheels evaluated were adequate for mustard and cabbage under soil moisture conditions and soil type found in these plantings. Uniform plant emergence with all covering devices and presswheels was attributed to adequate rainfall within three days of planting that effectively closed the seed furrows after planting. Different results may be found if planting in heavier soil type, under drier or wetter soil conditions, or if precipitation does not occur within a few days after planting. We observed that the paired arms device did the best job of covering, and we have switched to this at the station. Operating the seeder without a covering device, regardless of presswheel attached, left the seed furrow open and seed exposed.

Seeding depth and opener type

Seeding depth affects stand establishment. A common recommendation is to place seed at a depth equal to three times its diameter. With small seeds, such as mustard and cabbage, however, this recommendation results in planting so shallow that heavy rainfall soon after planting can wash away soil covering the seed. Also, a dry soil surface will limit moisture to the seed planted at a depth too shallow. Both of these problems can be alleviated by altering seeding depth.

We planted three vegetables, mustard, turnip and cabbage, at depths of 0.2 inch, 0.5 inch, 0.7inch and 1.0 inch with a Stanhay belt seeder in April, August and October 1997.
We also evaluated two types of openers, the two-line coulter opener and the scatter shoe opener. On these same dates, we planted mustard and turnip with a Stanhay belt seeder equipped with a two-line coulter opener and with a Gaspardo vacuum seeder equipped with a scatter shoe opener. The coulter opener distributed the seed into two small individual furrows spaced 2 inches apart. With the scatter shoe opener, the seed were dropped through a pattern of steel pegs that scattered the seed randomly over a 3-inch-wide furrow.

Soil moisture at the April planting was adequate. Soil moisture at the August and October planting dates was low, but adequate rain fell within five days of planting. Seed emergence was not consistently affected by seeding depth under the optimum soil moisture conditions experienced in these studies. Overall, planting at depths of more than 0.5 inch was not detrimental to plant emergence. We recommend planting depths of 0.5 inch to 1.0 inch for small seeds, such as mustard, turnip and cabbage, to protect against seed washout from torrential rains and to provide better seed placement in soil moisture under drought conditions.

Plant emergence at all planting dates was greater in plots seeded using the 2-line opener than those seeded using the scatter shoe. The problem observed with the scatter shoe was the opener/coverer interaction. The scatter shoe opened a broad furrow and scattered seed randomly over the furrow bottom. The standard drag coverer then dragged a wave of soil over the furrow, and this soil wave appeared to displace some of the seed. Inconsistent depth control of the opener itself was another problem observed with the Gaspardo seeder. 

Regina P. Bracy, Associate Professor; Richard L. Parish, Professor; and Joe McCoy, Research Associate, Hammond Research Station, Hammond, La.

(This article was published in the winter 1999 issue of Louisiana Agriculture.)

10/8/2009 1:30:55 AM
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