Regina P. Bracy, Parish, Richard L. | 6/14/2005 6:36:48 PM
Regina P. Bracy and Richard L. Parish
An important feature of a precision seeder’s performance is its ability to place seeds singularly a given distance apart. Manufacturers of precision vegetable seeders promote their products as more accurate at seeding uniformity than typical agronomic seeders. Based on previous research with vegetable seeders, we decided to compare the seeding uniformity of precision vegetable seeders with agronomic seeders.
For our study we chose the Stanhay model S870 (belt) and Gaspardo SV255 (vacuum) precision vegetable seeders and compared them with the John Deere 7200 MaxEmerge (finger-meter) and Great Plains 8030 (brush-meter) agronomic seeders for seeding uniformity and precision. Each seeder uses a different mechanism for singulating the seed, which provided a basis for comparison of singulation methods. All seeders are well-known brands and readily available to growers.
The seeders were operated over a 20-foot-long greased board at a ground speed of 1.5 miles per hour. Seed spacing measurements were recorded over a center distance of 10 feet. The ground speed was based on manufacturer recommendations for vegetable seeders (to minimize skips that can result at higher plate or belt speeds). Although the ground speed was slower than typically used for most agronomic seeders, all seeders were operated at this speed for consistency in testing and to accommodate the accurate placement of the equipment over the greased board. The board was coated with grease to prevent seed from bouncing and to retain exact placement of the seed.
Soybean seed was used to evaluate the seeders because of its spherical shape and medium size. Based on past seeder research, we know that better seeding uniformity can be expected with spherical seeds. Since the agronomic seeders tested have metering components sized for agronomic crops such as corn, cotton and soybean seeds, we could not realistically expect the agronomic seeders to meter small vegetable seeds such as broccoli or mustard.
Five measurements (mean seed spacing, skips, multiple seed drops, single seed drops and precision of seed spacing) were used to evaluate seeder uniformity. Mean seed spacing is a standard seeder calibration check used by growers and determined by catching the seed while the drive tire is rotated. Multiple seed drops indicated the percentage of seed spacings that had more than one seed dropped in a spot. Skips or missed seed locations were the percentage of spacings where a seed should have been placed but was not. Quality of feed index indicated single seed drops. Precision of spacing indicated the accuracy of the seed placement after omitting the outliers (missed and multiple seed drops). Precision was a measure of the uniformity of spacings classified as singles. Skips, multiple seed drops and single seed drops were measures of singulation.
Mean seed spacing for all seeders was close to the spacing expected but did not give an accurate indication of seeder uniformity. Although not considered a valid measure of uniformity by the authors, mean is the only measure a grower can readily use to determine seeder performance. This measure was included to illustrate the fallibility of the typical seeder calibration checks (catching the seed while the drive tire is rotated) used by growers for determining seeding uniformity of the seeder.
Skips were lowest with the Stanhay (4 percent) and John Deere (8 percent) seeders (Table 1). The Stanhay belt seeder also had the lowest percentage of multiple seeds per drop and highest single seed drops. Although Stanhay had the best precision (seed spacing uniformity of single seed drops), precision was not considered acceptable for any seeder tested.
The Stanhay vegetable seeder had the best seeding uniformity and precision spacing of all the seeders tested. The Gaspardo vegetable seeder and the John Deere agronomic seeder were comparable in seeding uniformity and precision although fewer skips were noted with the John Deere. The Great Plains agronomic seeder, which is not designed to be a precision agronomic seeder, had a high number of skips and multiples and poor seeding precision.
Precision and uniformity varied with the seeder tested. Seeding uniformity was good with one vegetable seeder (Stanhay) and fair with the other (Gaspardo). Uniformity with the agronomic seeders was fair with the John Deere but unacceptable with the Great Plains. If medium to large spherical seed (such as peas and beans) are being planted, adequate seeding uniformity can be obtained with an agronomic seeder such as the John Deere MaxEmerge. When planting small vegetable seed or irregularly shaped seed, growers would obtain better uniformity and less waste of expensive vegetable seed if they used a belt seeder specifically designed for vegetable crops.
(This article appeared in the winter 2003 issue of Louisiana Agriculture.)