Soybeans

Soybeans (glycine maximus) are an ancient crop from the Orient.  The first written record of
their cultivation was in 2838 BC in China.  The plant made it to Europe in 1712, and then came
to the USA via clipper ship in 1804.

Most of the early use of the plant was to make legume hay.  It was also plowed under as a green
manure crop.  The first use of a combine to harvest soybeans was in 1924 by the Garwood
Brothers of Stonington, Illinois.  Until then, reaper binders and stationary threshers were used
and the seed shattering was excessive.

Several different cropping systems are used by the Northern Grain Growers (NGG) to bring this
crop to the bin.  A good seedbed that is level is needed, and culti-packing may be used.  Soybean
seed needs to absorb 50% of its weight in water in order to germinate, so good seed-to-soil
contact is essential.  By comparison, corn needs 30% of its weight in water to germinate, while
small grains need only 10% water.  The flat level seedbed is needed for harvest, since the plant
sets its seed close to the ground.  Thus the cutter bar must cut close to the ground to harvest all
the soybeans without picking up dirt.

Soybeans can be planted on 30-inch rows with a corn planter.  High populations (160,000 to
200,000 plants per acre) are necessary, so special soybean seed cups or drums may be needed.
Soybeans can also be planted with a grain drill on 7 to 10 inch rows, in which case the
population should be even higher (270,000 to 280,000 plants per acre).  The best drills for this
purpose have double disc openers and packing wheels over the row.  Since soybeans range from
1800 to 2700 seeds per pound, adjustments must be made to the pounds per acre to get the
desired population of plants.

The seeds are planted 1.5 to 3 inches deep.  All seed must be inoculated with nitrogen-fixing
bacteria.  If no soybeans have been grown on the field before (which is the typical case in New
England), double the rate of nitrogen-fixing bacteria should be used.

The 30-inch row spacing allows for row crop cultivation, while7-inch rows canopy over quicker
to smother weeds.  In either case, a pre-emergence cultivation with a tine weeder or a rotary hoe
may be useful.  After the soybean plants are 4 to 8 inches high, they can be cultivated again.
Soybeans should not be cultivated when they are below 4 inches in height, since the hypocotyl
arch or neck that the seedling forms as it emerges from the ground is very brittle and can be
broken, thus killing the plant.  As with all crops, a good crop rotation is an important part of
weed control.

At harvest, floating cutter bar heads or row crop heads have the lowest field loss.  Most soybean
loss during harvest comes from shattering at the head of the combine. Soybeans generally thresh
easily with a lower cylinder speed and medium cylinder spacing.
It is often better to wait until after frost to harvest soybeans, as this allows the soybean stems and
weeds to dry for easier harvest.  Soybeans should be dried to below 13% moisture for safe long-
term storage.  If heated air is used, keep the temperature low (under 1200 F) to avoid heat stress
cracks in the soybeans.

Ken Van Hazinga