Special Processing and Treatment of Seeds

LAURENCE H. PURDY, JESSE E. HARMOND, AND G. BURNS WELCH.

MOST agricultural seeds need some kind of processing to make them easier to handle.

The processing may remove or change some objectionable structure or give specific information about the seed lot or protect the seeds from pests.

It may be done for a specific purpose on a particular type of seeds (for example, delinting of cotton), a group of closely related seed types (scarification of legumes), or a large number of seed types (seed treatment).

This processing is done after cleaning and separating have made sure that a particular lot is pure as to variety.

The value of special processing is illustrated by results from the use of delinted cotton seed. One ton of undelinted seed will plant 60 acres. One ton of undelinted seed gives 1,700 pounds of delinted seed, which will plant about 210 acres, allow more uniform plantings, be free of certain lint borne pathogens, and permit better coverage with chemicals.

The treatment with chemicals to control certain seedborne and soil-borne diseases, such as damping-off, or seed decay, and some smut diseases, is another form of special processing.

Indeed, the application of effective chemicals to seed of wheat is the only control of common wheat bunt when resistant varieties are not available or have broken down.

The use of ineffective chemicals on seed, which is like planting untreated seed, accounts for large losses of crops.

In the Pacific Northwest, for example, a comparison of hexachlorobenzene and a mercury fungicide to control soilborne common bunt of wheat was made by planting alternate drill strips with seed treated with each material across a grower's field. An average of 16 percent of bunt developed in strips planted with seed treated with hexachlorobenzene; 65 percent of bunt developed with the mercury fungicide. A yield of 55 bushels an acre was obtained from the strips treated with hexachlorobenzene. Losses due to the use of the ineffective mercury fungicide were 50 dollars an acre.

SEED OF COTTON still has a small amount of lint or fuzz on the surface after ginning. The fuzz makes it hard to plant because the seeds stick together and do not flow easily.

Mechanical delinting is like ginning. Saws in the delinting equipment are closer together and have finer teeth. Lint is cut as close as possible to the seed without breaking the hull. A small amount of fuzz is left on mechanically delinted seed.

The seeds, metered by a fluted roller, enter the roll box, in which a float revolves them so that the saws come in contact with all seeds. A saw cylinder, with more than a hundred fine saws, is under the roll box. Saws project a short distance into the roll box through narrow slots and cut the lint from the seeds. Cut lint is removed from the roll box by the revolving saws. A large brush behind the saw cylinder brushes lint from the saw teeth. Lint is blown to the separator, or condenser-, where it is separated from the airstream and rolled into large rolls or pressed into bales.

Flash or flame processing removes more of the fuzz left on mechanically delinted seed. Flash furnaces have a vertical duct with butane burners in the side of the duct at the bottom. Seeds are metered onto a vibrating conveyor, which feeds them into the furnace at the top. They usually pass through two furnaces operated at 2,400 F. to insure removal of lint.

Thereafter the seeds pass over an air-screen cleaner, which removes immature seeds and foreign material.

Chemical delinting removes all lint by an acid.

In what is called the dry process, hydrochloric acid and sulfuric acid are mixed to form a gas, which is piped into a revolving tank. A reaction between gas and fuzz on the seed in the tank causes the fuzz to crystallize. Heat hastens the reaction. Then the seeds are dumped into a revolving perforated cylinder, which removes the crystallized lint. An air-screen cleaner removes immature seeds and foreign material after all the lint has been removed. Anhydrous ammonia neutralizes acid on the seeds in a revolving tank.

In a wet process, an acid solution is applied to seed until the fuzz is crystallized. The seeds are rinsed to remove crystallized fuzz, and the acid is neutralized. Then they are dried and passed over a cleaner, which removes immature seeds and foreign material.

MULTIPLE GERMS and irregularities in size, shape, and density have made accurate planting of sugarbeet seeds difficult. New methods and machinery enable us to get seeds of more uniform size and fewer germs in a seedball.

The first attempt to get single-germ seeds was to cut them in a machine that had a vertical carborundum wheel and a metal shear bar, between which the seeds passed. The segmenting process injured the seeds, so that germination often was poor and seedlings were damaged. Less drastic methods were sought.

Decortication involves the use of two units. One has a metal bur plate above a rough, horizontal stone. The other is a neoprene pad mounted above a smoother horizontal stone. Whole seeds are fed into the bur machine through the top and pass between the bur plate and the revolving stone. This process reduces the size of seed units by removing outer corky parts of the seedballs, which then pass between the pad and its revolving stone. Here more of the corky portion of the seedball is removed, and the number of germs in the larger seed-balls is reduced further. The mixture of seeds and dust is separated by a cleaner and grader. Seeds are then delivered to a gravity table or aspirator to remove light or incomplete units.

Decorticated seeds have a greater density than whole seeds and about one-third the volume of the whole seeds. Decorticated seeds also are smoother and more uniform in size and are more easily planted than whole or segmented seeds.

Decorticated seeds are superior to segmented seeds in all respects except degree of singleness. When germination is less than 50 percent, better stands and higher percentages of single plants are obtained with decorticated seeds than with segmented seeds. The work of singling, or thinning, is cut by 25-30 percent when decorticated seeds are planted.

SOME HARD SEEDS are scarified-scratched to break their impermeable layer of surface cells, which form a moisture barrier. Unscarified seeds of this type do not readily absorb the moisture needed for germination.

Legumes, asparagus, and okra usually contain a high percentage of hard seeds, which do not give a uniform stand if their seedcoat is not broken.

Scarifying can be done in several ways by buffing after treatment with a special oil; treating the seeds with acid or heat; irradiating them electrically; and abrading them mechanically.

Scarification has to be done with little damage to the seeds.

The industry mostly uses mechanical scarification. The acid method is used more extensively on seeds of cotton.

Irradiation has been used experimentally on corn, cotton, some vegetables, and legumes.

Mechanical scarifiers pass the seeds over some abrasive surface, such as sandpaper, or a carborundum stone. Airstreams separate hulls and chaff.

One machine has a stationary disk and a rotating disk. Seeds fed into the center of the top disk fall on the rotating disk. The seeds travel outward and strike abrasive paper at an angle that removes hulls and breaks the outside layers. A jet of air removes the hulls, dust, and light stems.

In another huller-scarifier, seeds are fed into the center of a rotating distribution disk, which throws the seeds outward, where they strike a carborundum stone ring. The seeds drop through a funnel to a second rotary distributor and abrasive stone. The dust and chaff are separated from the seeds in a cyclone separator.

In a rotary drum-type scarifier, seeds are drawn into the drum and moved through it by air. The seeds are hulled and scarified when they strike segments of carborundum stone embedded in the drum surface. Hulls are removed by a suction fan. The severity of scarification can be regulated.

The machines have capacities up to 100 bushels an hour.

SAMPLING EQUIPMENT used to obtain correct and representative samples of seed lots generally are simple devices. One automatic type is run by an electric motor.

Commonly used samplers for grain in bags and in bulk are probes or sleeve-type triers of brass or aluminum tubing. They have a hollow inner tube with slots or compartments and an outer tube, or sleeve,with a like number of slots. Bagged grain usually is sampled with a six-slotted, 30-inch probe 1 inch in diameter. Small seeds, such as clover, are sampled with smaller probes.

A probe for bulk grain has 11 compartments separated by partitions in the inner tube. The probe is inserted in the grain, and the inner tube is turned a half turn to allow the grain to enter the compartments. Another half turn closes the compartments. The tube is withdrawn, and the sample is removed. Grain from each compartment is inspected separately.

A representative sample of grain is obtained by probing the bulked grain in five or more places. Seven or more places are probed to get a representative sample of flax.

Bulked grain that is being loaded aboard ships can be sampled with a spout sampler, or pelican. It is used to cut the stream of grain at frequent and regular intervals to assure the collection of a correct and typical sample. The pelican, a leather basket, is attached to a pole 8 to 10 feet long. Samples obtained with it are later reduced in size by running the sample through a sample divider.

A probe, designed for sampling corn in cribs, is inserted between the boards of the crib. Corn is shelled from the ears by rotating and rocking the handle of the probe. Shelled corn falls into the opening of the probe. A true sample can be obtained by repeated probing of the crib.

A semiautomatic sampling device, operated manually, is used to collect samples from seed cleaners. It is activated by pulling a rope or chain at the work-floor level. When collecting the sample, a small cup is turned to allow seeds to enter the cup at the discharge of the cleaner. The sample falls to the floor through a pipe attached to the sampling device.