Agriculture Reference
In-Depth Information
3.5.6 Soil Preparation and Planting
Production of edamame and some tofu varieties are manually cultivated in parts of
Asia. Soybean production in the rest of the world tends to be a completely mechanized
system for oil grain. Soil preparation and planting are done with equipment similar
to that used for maize and sorghum. Under conventional tillage systems, a field will
be plowed or disked to break up clods and leave a friable, weed-free seedbed.
Minimum, or zero-tillage, systems permit planting without tillage or other soil
preparation.
Soybeans are planted in rows spaced from 7 to 30 inches apart. Wide-row spacing
permit tractors to pass through the field without damaging plants. When planted in
narrow rows, all fertilizers and chemicals are applied at planting to reduce plant
damage from tractor tires. In some parts of the United States, soybeans are planted
after harvest of wheat or barley in early summer. This permits the harvest of two
crops in the same year. In more tropical climates this is routine practice.
3.5.7 Fertilization
Because soybean is a leguminous crop, it does not require a nitrogen fertilizer to yield
well. In fact, application of nitrogen fertilizer can have the effect of reducing or pre-
venting nitrogen fixation by the symbiotic Rhizobium bacteria. Every kilogram of
grain harvested will remove 16 g of phosphate and 23 g of potash. With a good yielding
crop of 1500 kg/ha, at least 24 kg of phosphate and 34 kg of potash will be removed.
These nutrients must be replaced to maintain adequate levels of soil fertility.
In addition to chemical or organic fertilizers, it is sometimes necessary to inoculate
seeds with Rhizobium. Commercial preparations of Rhizobium were first sold in the
United States in 1905. If a field has not been planted to soybeans for 5 to 7 years, it
is recommended to inoculate the seeds with Rhizobium before planting.
3.5.8 Weeds, Insects, and Diseases
Until the 1990s, weeds were a serious problem with soybean. Because the crop grows
relatively slowly, many weeds were able to outgrow the soybean in early stages and rob
it of nutrients and moisture. Available herbicides carried risks of damage to the crop. In
the spring of 1995, the U.S. Environmental Protection Agency (EPA) approved the
planting of herbicide-tolerant soybeans. In practice, farmers could spray a growing
crop with herbicide and kill all weeds. This meant that several tillage operations
before planting and a herbicide application after planting could be eliminated. Since
the introduction of this trait, plantings of herbicide-tolerant soybeans have captured
about 65 percent of the market in the United States.
Various diseases can cause serious yield losses in soybean. Most strike in the seed-
ling stage. Phytophthora root rot, pythium root rot, and rhizoctonia root rot are the most
common diseases affecting seedlings. Some varieties have moderate resistance to some
of these diseases. A combination of varietal resistance and seed treatment with a fun-
gicide work best to prevent losses to these diseases.
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