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Soybean Production Guidelines

PLANTING DATE
Soybean planting should begin when the soil temperature is 55-60 F at four inches below the soil surface with forecasts for warm weather for the upcoming week. In average years, the optimum planting date is usually between May 10-20th. Planting soybeans before May 10th makes them a far greater risk than corn from frost damage since at emergence the growing point (just above the cotyledons) is exposed; therefore, a frost can kill the plant.

If soybean planting gets delayed, don't change from adapted varieties to earlier varieties until after June 15th. Soybeans are much more forgiving than corn concerning yield reductions from late planting, generally yield loss is less than 10% until about mid June. Unlike corn, soybeans are a photoperiod sensitive crop. Vegetative growth is determined and flowering is initiated by the length of darkness. Since early planted varieties are triggered to flower by a shorter night period than a fuller season variety, and all late planted soybeans are shorter due to less vegetative growth, too much yield is lost when changing to early varieties before mid-June. Plant corn first, then evaluate for soybean planting.

PLANTING POPULATION ROW WIDTH
Generally, the typical final stand should be around 150,000 live plants per acre (ex. drop 170,000 seeds/acre if germ in -90%), increase this by 10% or more in drilled situations. Be sure to plant by seeds per pound and not by pounds per acre, since seed size will vary between varieties and years. Also, vary planting rates to compensate for germination differences between varieties. Soybeans should be planted at a depth of 1 to 1 and 1/2 inches, and never deeper than 2 inches. If late planting becomes a reality, increase plant populations to 200,000 to 225,000 plants per acre, since late-planted soybeans are shorter (less vegetative growth) and more plants are needed to maintain the yield level of a normal date. Late planted soybeans typically lodge less, shatter less, have slightly less oil content and slightly higher protein levels.

Soybean yield response to row spacing generally increase with narrow rows, which provide more equidistant spacing between plants. Narrow rows have quicker canopy closure, which conserves water, helps reduce weed seed germination, and allows plants and roots to more efficiently use sunlight, water, and nutrients before competing with each other. Yield response to narrow rows is less pronounced in the low yield environment (greatest response is in the high yield environment).

PLANTER BOX TREATMENTS
Cool, wet weather patterns, soil types with slow drainage, and reduced or no-till practices that result in cooler and wetter soils may warrant a planter box treatment. Planter box treatments (fungicides) provide protection against water molds (Pythium and Phytophthora) or other soil or seed borne fungi (Rhizoctonia, Fusarium, Phomopsis, and Macrophomina species). Fungicidal treatments will not improve the seeds germination, but will protect against seed rots, damping off, seedling blights, with some activity on pod and stem blights caused by these diseases and pathogens. Ongoing studies have indicated 5 up to 14% increase in grain yields (treatment vs. no treatment in no-till), and a 14 up to 30% increase in stand establishment.

FERTILIZATION, INOCULANTS, AND LIME
Nitrogen

Soybeans can obtain up to half of their nitrogen requirement from the air when nitrogen-fixing rhizobia bacteria are present in the soil. Additional nitrogen requirements come from carryover and microbial soil mineralization. Therefore, by maintaining the proper rhizobia environment, nitrogen application is not recommended.

Inoculants

Since legumes require different rhizobia it is important to inoculate soybeans where a well-nodulated soybean crop has not been grown for 3 to 5 years depending on the soil type. In soils with more than 90% sand, it is recommended the field be inoculated annually. Additionally, the rhizobia bacteria do not function in soils with a pH below 5.0, and supplemental molybdenum (necessary for nitrogen fixation) and should be added to the inoculate for soils with a pH of 5.0 to 6.0, or add lime to boost pH to between 6.0 to 7.0.

Lime

Lime should be profitable if soil pH is 5.8 or below. The best time to apply lime for all legumes is in the preceding year mixed into the top 6 inches of soil. Liming acid soils enhances microbial activity, which mineralize soil, making nitrogen and phosphorus available to the plant.

Phosphorus

Generally, where soybeans are grown in rotation with corn the soybeans will not need additional fertilization with phosphorus as long as the phosphorus test is about 15 ppm Bray 1 Phosphorus, the goal for optimum corn production. Yield response to applied phosphorus will probably occur below 12 ppm Bray 1 Phosphorus. Phosphorus, if needed, can be applied broadcastal then incorporated or banded not more than 15 inches apart 4 to 6 inches deep, or as a starter at 1 inch to the side and or slightly below seed depth. Never apply fertilizer in the seed furrow.

Potassium

Potassium soil levels are normally high enough not to justify adding potassium, except on very sandy soils. Take soil tests and fertilize and lime based on a sound soil testing program, don't forget to consider the micronutrients as well.

Iron Chlorate

Finally, some soybeans grown in calcareous soils may become chlorotic because iron is tied up in the soil, use our tolerant varieties and in some cases, applying an iron chelate with the seed at planting may be justified.

STAGES OF DEVELOPMENT
Soybean development is divided into vegetative (V) and reproductive (R) stages, VE is emergence, VC is unfolding of the unifoliate leaves, then the following stages (VI, V2,. . . Vn) are marked and defined by the uppermost fully developed leaf node. A fully developed leaf node is one that has a leaf with unrolled or unfolded leaflets above it. V3 then, for example, would have four nodes with unfolded leaves, and so on. Each node is an auxiliary bud (auxiliary growing point), so even severe stem and leaf defoliation above the cotyledonary node produces new branches and leaves. One open flower at any node signals the beginning of the reproductive (R) stages.

There are 8 reproductive stages all referring to development on the main stem. R1 (beginning bloom) is one open flower at any node. R2 (full bloom) is an open flower at one of two upper most nodes with a fully developed leaf. This stage marks the beginning of rapid dry matter and nutrient accumulation. R3 (beginning pod) is a pod developing at anyone of four upper most nodes. R4 (full pod) the pod is 3/4 of an inch long developing at anyone of four upper most nodes. R5 (beginning seed) 1/8 inch seed is developing at anyone of four upper most nodes.

Late pod formation (R4.5 to R5.5) is the most critical time for yield loss due to pod abortion. Flowering can no longer be initiated to compensate for losses. Therefore, stress at this time reduces yield, due to a reduction in pods per plant. If irrigation is available, this may be the time it is warranted. R6 (full seed) plants have a pod containing a seed that fills the pod cavity at anyone of four upper most nodes. As soybeans develop past R6 any stresses are not as critical, but can reduce the seed size, seeds/pod, and pods per plant. R 7 (beginning maturity) is when one normal pod has reached its mature pod color. Stress occurring at R 7 or after has no effect on yield. R8 (full maturity) 95% of the pods have reached their mature pod color. Five to ten days of good drying weather will move soybeans to less than 15% moisture and close to harvest.

HARVEST

Harvest soybeans when moisture is between 13 to 15% for maximum weight and to minimize field losses like shatter or lodging. Soybeans drier than 10% are brittle and more likely to split during handling and harvest, plus germinations are likely to be lower. Soybeans can be winter stored at 13%, stored for 1 year at 12%, and at 11 % or less for more than 1 year.

In summary, to maximize soybean production,

• Plant adapted varieties at proper seeding rates and at optimum dates.
• Fertilize and inoculate based on sound soil tests and cultural practices.
• Scout, monitor, and control pest (weed, insect, and disease) populations as needed.
• Finally, keep harvest and storage losses to a minimum.

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