The length of the growing season varies from 50 to 200 days, depending on the variety, weather, latitude, etc. For dry harvest, soybeans should be allowed to stand in the field while the pods dry and mature, turning a buff to yellow colour, Figure 6. During this time, the leaves will first turn yellow and then drop off. The fully ripe beans are left to dry in the fields; the old brown stems and pods are left standing until dry, with the moisture content falling to about 13 percent. Some small farmers check seed moisture by just cutting few pods, moving them in the air to listen to its dry sound. Others remove the seeds from the pods and apply some pressure with their teeth.

 Figure 6. Soybean field ready for harvesting in the Yaqui Valley, Sonora, Mexico.

Soybeans are harvested over a relatively short period of time. In the United States, Mexico and some other countries, soybeans are harvested in the fall of the year. Therefore, the initial soybean marketing is a highly seasonal activity with the result that the beans are gathered and placed in storage for utilization over the entire year. Depending on circumstances, the grower may hold the beans in storage, either on the farm or in private storage space, or sell his beans for cash.

Most of the soybeans are mechanically harvested. In the fall, combines (Figure 7) run day and night to bring in the harvest before the fall rains. The machine moves down one to several rows (depending on the size of the combine) and pick up leaves stalks and pods. The seeds are threshed out from pods into a hopper and moved into a transport truck. All other parts of the plants are blown back out onto the field. In the less developed countries, harvesting is done by a two- or four-row cutter (Figures 8 and 9). The plants are cut 1 to 2 in. above the surface of the soil, usually in the early morning when the presence of dew prevents shattering. Hand cutting by sickles (Figure 10) is another way to harvest soybeans, particularly for beans grown in a small field. The harvested plants are collected, dried and finally threshed (Figure 11). Thresher machines similar to that of Figure 11 are commercially available in the United States http://www.Almaco.com or Brazil http://www.Industriascolombo.com.br. The price oscillates between US$ 5 000 and US$ 7 700. See the Annex (page 87) for technical specifications of these type of machines.

 Figure 7. Modern combine for soybean harvesting, left; front view; right; back where all other parts of the plants are spread onto the field.

 Figure 8. Equipment used for soybean harvest in the less developed countries.

 Figure 9. Agricultural implement used with the equipment in Figure 8. to reduce harvesting loss.

 Figure 10. Hand cutting by sickles.

 Figure 11. Equipment for soybean threshing.

Harvesting a backyard crop of soybeans for home use is a little more labour-intensive. If you are growing a small quantity of beans, you can cut and thresh them by hand. Cut the stalks, stuff them in a burlap bag, then trample them, beat them or run them over with your pickup. The resulting tangle can be winnowed by pouring the beans from one bucket to another, either outdoors in a brisk breeze, or in front of a large fan.

The beans may also be harvested in the green stage, you can gather, cook and freeze them, as you would garden peas. Steam the green, still-tender pods for about ten minutes, pour off the water and remove the hull. This will be a slow process. Some folks simply pull the green shell between their teeth and pop out the green seeds that way. Green soybean harvest may be stretched over several weeks, as the beans at the base of the stalks dry first, then gradually the ones higher up--very much like garden peas.

Reliable data on the true level of soybean postharvest losses are not available. It is really a difficult task to evaluate losses that occur during all phases of the postharvest system. Postharvest losses must include both quantitative (weight loss) and qualitative (nutritional, functional, or hygienic) losses caused by various physical, biological and mechanical factors, which the beans are exposed to.

In general, losses of food grains through spillage and breakage are reported to be lesser in manual harvesting than in the use of mechanical devices (FAO, 1984). Soybean harvesting loss data are scarce throughout literature. A study carried out in Monte Alegre de Minas, MG, Brazil (Reis et al., 1989) reported losses due to mechanical harvesting of soybeans in the range of 2 to 4 percent, depending on the type of cylinder attached to the combine and the hour of harvesting, Table 14. Manual harvesting caused less seed damage than mechanical harvesting, Table 15. In this study, losses were measured by collecting the pods and beans scattered on the ground and, separately, the pods and beans left on the plant stumps. They used two types of cylinders in the combine: a toothed cylinder for threshing out the grain and one with steel bars mounted longitudinally on the cylinder. The toothed cylinder provoked a higher seed loss (1.17 percent) and less damage than the cylinder with the steel bar, Table 14. Seed losses increased as the hour of harvesting progressed and seed moisture decreased. Seed damage (cracked and split seeds) increased during the day as levels of humidity reduced, Table 15.

Source: Reis et al. (1989).

Source: Reis et al. (1989).

The harvesting losses estimated by a soybean grower (medium-scale farmer) in Culiacan Valley, Sinaloa, Mexico (Godoy, 2000), using the equipment shown in Figure 8, was 150 kg per hectare (about 7 percent). If the agricultural implement shown in Figure 9 (with a value of US$ 12 000) is attached to the equipment illustrated in Figure 8, harvesting losses are reduced significantly (almost to 1 percent). Kowalczuk (1996) reported soybean harvesting losses £ 6 percent when harvesting was carried out with the Z056 "Bizon Super" grain combine harvester equipped with a floating cutting bar. Scott and Aldrich (1970) reported harvest losses between 5.4 and 12.2 percent depending on the height at which the combine cutterbar was operated. The lower loss corresponded to a height of cut of 3.5 inches and the higher to 6.5 inches.

It is estimated that the average time spent cutting the plants by sickles runs from 80 to 100 man-hours per hectare, that is, 10 to 12 work-days per hectare (Godoy, 2000).

Mechanical harvesting with combine-harvesters spent between 1 to 2 hours per hectare, depending on the machine capacity and how well the land was levelled and weeded. The combine works efficiently if the plants stand erect and reach maturity simultaneously. If the grower does not own a combine and wants to harvest with rapidity his beans, then he contracts the service of harvesting, which includes the rent of the combine and the operator’s salary, at a rate of US$ 40 per hectare (Godoy, 2000).