Harvesting the Seeds of Grasses and Legumes

JESSE E. HARMOND, JAMES E. SMITH, JR., AND JOSEPH K. PARK.

IT IS NOT easy to harvest the seeds of grasses and legumes. Many methods and special machines are needed, and they get only a part of the seed.

Several factors are involved variations in the size, weight, and maturity of the seeds; plant types; the height and spacing of the plants; the growing season; and time of harvest.

Some examples: Velvet bentgrass has 10,800,000 seeds to a pound; field peas have only 1,800. Subterranean clover may bury its seed in the topsoil; sudangrass will grow to 8 feet tall. Vetch seed is large and dense; the Arizona cottontop has a light, fluffy seed, covered with short, white hairs.

The seeds of some species ripen evenly; the slender gramagrass has seed in all stages from the bloom to maturity, from June until frost.

Some seed plants are grown in solid stands. Others may be sparsely spaced in rows. Some kinds have a single stem; others grow in a clump.

A survey by research engineers in the Department of Agriculture disclosed that a farmer might be harvesting less than one-half of the seeds he produced 33 percent of the crimson clover crop as pure live seed; 23 percent of the subterranean clover; 65 percent of the Alta fescue; 53 percent of the hairy vetch; 46 percent of the alfalfa; 25 percent of birdsfoot trefoil; and 40 percent of the Ladino clover.

To combat such heavy losses of seed, improved machines and methods are being developed continually. Some of them we consider here.

THE COMBINE, developed to harvest cereal grain crops, has been modified to handle small seeds and is the chief machine used in harvesting crops of grass and legume seed. All the different types of combines have been used, tractor drawn and self-propelled, with cutting mechanisms 6 to 18 feet wide. Small harvesting machines save more seed than the larger ones.

Modifications of the combine include a speed control for the cleaning air fan; baffles for air distribution; rubber-covered angle bars in place of a spike-tooth or rasp bar cylinder and concave; special sieves for the combine cleaning shoe; a variable speed control for the threshing cylinder; a sheet metal pan under the chaffer tailing extension; and check curtains behind the threshing cylinder.

The weather, the stage of seed maturity, and the kind of seed crop determine the alterations necessary.

Rubber-covered angle bar cylinder and concave often are used to thresh crimson clover seed, which is hard to remove from the pod yet damages easily.

The size and shape of the openings of the special sieves on the combine cleaning shoe accommodate a particular seed. For example, a 24 by 24 wire mesh screen is recommended for red-top seed. The adjustable sieve can be regulated to accommodate many seed sizes. To handle dallisgrass, the sieve is set one-half open and the cleaning air is shut off. With the variable cylinder speed control, the cylinder speed can be increased to handle seed, like crimson clover, that is hard to thresh. It can be reduced to handle seed that is easy to thresh.

The metal pan under the tailing extension keeps seeds, stems, and leaves from falling into the return elevator and being rethreshed. Check curtains back of the cylinder deflect the discharging material down to the rack so that the seed can be shaken out of the straw and on to the shoe for cleaning.

Rubber rolls may be mounted ahead of the threshing cylinder for crushing seed pods in crops like alfalfa and flax. For threshing alfalfa, the cylinder speed can be reduced as much as 1,000 revolutions per minute; there is less damage to seed, and the percentage of unthreshed seed is no higher.

Four-way automatic leveling devices are used in hillside combining to keep the threshing and cleaning mechanism level while operating on the side of a hill. Without the leveling, the material would crowd to the low side of the cylinder, rack, and the cleaning shoe, thereby causing cylinder chokage, inefficient separation of the seeds from the straw, a slow forward speed, and greater loss and damage of seeds.

A vertical sickle at the end of the cutterbar cuts the tangled crop and separates the cut and uncut standing crop, so that there is less chokage and seed shatter in crops like vetch. The rotary screen cleaner, mounted in the discharge of the combine grain bin auger, screens out dirt and small seeds of weeds before the seeds go into the sacker.

Lift fingers on the cutterbar raise a low-growing crop or a down crop above the sickle so it can be cut. A vacuum attachment under the combine can be used to reclaim shattered seed from the ground.

Special cutterbars, like the lespedeza bar, have more and smaller ledger plate guards and cut the crop near the ground. The double sicklebar has no guards, and both the top and bottom sickles reciprocate to cut heavier and greener crops without chokage.

Special reels can be used, like the tined reel, which lifts down crops, or the wind reel, which blows the crop into the cutterbar, instead of the revolving reel, which causes shattering.

Special gears reduce the forward speed of the combine without lowering the speed of the threshing and cutting mechanism. The possibility of cylinder chokage and overloading the rack and shoe is less.

As THE CROP gets drier, the seeds shatter more easily, but the setting of the concave clearance can be wider and the threshing cylinder can be operated at slower speed.

When the moisture is high, the cylinder speed is increased and the clearance is lowered to thresh the seed.

In direct combining, the standing crop is cut and immediately run through the combine to free the seed through their pods and separate them from the straw. When crop conditions, maturity of seed, and weather permit, direct combining is desirable. It requires less labor and equipment.

In windrow combining, the crop is cut and gathered into swaths or windrows to field cure. A pickup attachment on the combine lifts the cured crop from the windrow and feeds it into the combine, which threshes and separates the seed from stems and leaves. Windrow combining is used usually on crops whose seeds shatter before the plant and seeds are dry enough to combine and store.

To ANALYZE the operation of a combine, we recommend several steps:

Adjust the threshing cylinder speed and clearance to the crop that is being harvested.

Regulate the forward speed of the machine so that the crop will not overload the threshing cylinder, rack, and shoe.

Make a test run and analyze the operation by considering the combine in four sections feeding, threshing, separating, and cleaning and observe the operation of each part.

The feeding section consists of reel, divider, cutterbar, and feeding mechanism. The reel should hold the crop upright, while the sickle makes the cut, and then lay the straw gently on the draper. The reel speed should be 10 percent faster than the forward movement of the machine. The reel height should be adjusted so the slats Contact the straw just below the seed heads. The cutterbar knives and ledger plates should be sharp and in register.

The threshing section consists of a threshing cylinder and concaves. The discharging of unthreshed heads over the rack is caused by a low cylinder speed or excessive concave-cylinder clearance. Broken seeds are due to too high a cylinder speed, too little concave-cylinder clearance, or the return of threshed seed to the cylinder by the tailing return auger.

In setting the threshing cylinder, adjust the cylinder-concave clearance to one and one-half times the thickness of long seed or one and one-half times the diameter of round seed.

If excessive straw breakage is observed, increase the concave-cylinder clearance.

Adjust the cylinder speed so the seed is rubbed or knocked out of the seed pods or heads. Then gradually reduce the speed until some of the heads are unthreshed.

At this point, slowly raise the cylinder speed until only an occasional unthreshed seed head is found. Most of the occasional unthreshed seed is immature or partly filled seed.

The separating section consists of the beater cylinder, check curtains, and straw rack. Threshed seed in the straw discharge is due to overloading the rack, too slow a speed, or a worn check curtain.

Slow down the forward speed of the combine to prevent overloading.

Increase the rack speed to shake seed out of straw and renew the check curtain if the cylinder is throwing the seed over the rack.

The cleaning section has the fan, grain return, chaffer sieve, chaffer extension, and shoe sieve.

Excessive air blows seed over the chaffer sieve and out the back of the combine. Too large a volume of material also prevents seed from coming in contact with the sieve and dropping into the seed pan.

Adjust the cleaning air so the material is slowly agitated over the chaffer sieve. Precise air adjustment is required on light grass seed. For some grasses, the fan discharge is completely closed. The shoe sieve opening should be as large as possible without getting excessive straw and trash in the clean grain.

On grasses that are easy to thresh, the concave-cylinder clearance is widened to reduce the straw breakage, and the chaffer extension is blanked off by placing a piece of sheet metal under the bars to prevent material from being returned to the cylinder for rethreshing and possible damage.

IF A CONVENTIONAL grain binder is used to cut and bundle the seed crop, the bundles are shocked and left in the field to cure. The bundles are then threshed in a stationary thresher or a combine.

In dew areas, cutting and binding are done usually in early morning, while the humidity is high. After a curing period, the bundles are threshed in the afternoon when the sun has lowered the humidity.

To reduce seed losses, the binder often is altered by removing every other reel slat and installing catch pans under the binder deck and beneath cracks between the canvas and elevator to catch the shattered seed. Since the binding-shocking-threshing method involves a number of operations and takes more work and equipment, it is being abandoned, even though it may save more seeds than other methods.

IN SEED STRIPPING, the ripe seed is removed and the plant is left growing. A number of native grasses in the Great Plains, which cannot be harvested satisfactorily by any of the conventional methods, are stripped. Many kinds of shop-made strippers are in use.

Even under the best operating conditions, seed stripping is an inefficient way of harvesting seed; the stripped seed must be cured or dried before cleaning and storing.

A widely used machine is the bluegrass stripper, which removes the ripe seed with a ground-driven, spike-tooth cylinder so mounted that the revolving cylinder rakes off the mature seeds and discharges them into a seed hopper as the machine is pulled through the field.