Soybean Production

These agronomy tips have been compiled by members of MFA's professional agronomy staff. MFA has more than 100 certified crop advisors working across MFA's trade territory. Advanced professional training classes offered by MFA keep our employees informed of current production and environmental issues.

Cyst Nematode
Fertility
Planting
Seed Treatments
Weed Control

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Cyst Nematode

How do you take a soybean cyst nematode soil sample?
When managing nematode problems in fields, take random soil probes collected over the entire field and use one pint of soil to submit to the testing lab. When gathering subsamples use 15 to 20 to represent a field. Try not to allow field samples to represent more than 20 acres. If trying to identify a problem, take enough subsamples to get one pint of soil from the area that is suspected of nematodes. Sampling depth should be 6 to 8 inches. Make sure samples are moist and do not allow them to dry out or remain in the sun. Ship samples right away to the testing lab.

Should you use resistant varieties?
Take a look at the results of the egg count that comes back from the test lab. If any soybean cyst nematode eggs are present, you should put some management plan into effect to try to keep the nematodes at a manageable level. This will involve using crop rotations, planting some resistant varieties and planting some non-resistant varieties when egg counts have dropped off substantially.

What are nonhost crops and host crops?
Nonhost crops include alfalfa, small grains (barley, oats, rye, wheat), clovers (red, white, ladino), corn, cotton and sorghum. Host crops include beans (snap, bush, green, kidney), birdsfoot trefoil, clover (alsike, crimson, scarlet), lespedeza, sweet clover, chickweed, henbit and vetch (common, hairy, winter, crown). Using nonhost crops is one way to help reduce soybean cyst nematode reproduction.

Is planting soybeans after soybeans a good idea?
Continuous monocropping of any crop is not a good idea. If you have a soybean cyst nematode problem and you just try to manage it through planting resistant varieties, this can and probably will fail you over time. If egg count numbers continue increasing over time, potential yield will decline.

What type of damage do nematodes do to soybeans?
Soybean cyst nematodes inhibit growth and proper functioning of the root system in soybeans. Interference in the soybean root system can cause nutrient and water uptake problems in the plant. Plants may be less vigorous, stunted and yellow in appearance and may occur in oval or circular areas in the field. Yellowing of plant leaves often occurs in July and August.

What is the life cycle of the soybean cyst nematode?
There are three stages in the life cycle of the nematode. They consist of egg, juvenile and adult. The juvenile is what attacks and penetrates the soybean root. Females enlarge, break through the root surface, die and turn into brown cysts or egg cases. A single cyst may contain 200 to 400 eggs. A cyst can survive until conditions are right for the egg to hatch. During the growing season, there can be more than one generation. It is estimated that the complete life cycle may take as few as 24 to 30 days.

What are some of the ways that nematodes spread?
Soybean cyst nematodes actually move very slowly through the soil and will not be randomly distributed in a field. There may be pockets of them scattered throughout the whole field. Nematodes may move through wind, water, animals, birds, humans, farm machinery, vehicles and other tools used in fields. Nematodes may also move in soil peds through seed that is harvested, not cleaned and planted the following year. Thus, when moving from infected fields to noninfected fields, be sure to clean equipment.

Besides following crop rotations and using SCN-resistant varieties, is there anything else to help control this pest?
Always try to grow the soybean crop in the best possible environment. This means making sure the fertility level is at optimum conditions. Control weeds so they do not compete with the soybean for nutrients, moisture and sunlight. Some weeds are even hosts for the nematode. Plant the soybean in optimum conditions and protect it from diseases and insects. By ensuring the best possible growing conditions, you may help minimize potential impact by the nematode.

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Fertility

Should soybeans be fertilized?
Yes. Soybeans remove large quantities of phosphorus and potassium. Grain removal alone can remove .90 lbs. phosphorus and 1.5 lbs. potassium per bushel of soybeans. If you want to maximize yield, it is necessary to have a soil test with optimum phosphorus and potassium levels. Once soil test levels are at optimum levels, apply phosphorus and potassium based on grain removal.

Should soybeans be fertilized with nitrogen?
It depends. Soybeans require approximately 4.2 lbs. of N per bushel of soybeans. However, because the soybean plant is a legume, it produces its own nitrogen through rhizobium bacteria. If you are fertilizing the soybeans using diammonium phosphate (DAP) or monoammonium phosphate (MAP) fertilizer, you will be applying some nitrogen to the plant. Generally 0 to 30 pounds of N for a soybean plant in a preplant situation is fine. The soybean plant will use this nitrogen and then let the nodules start fixing nitrogen when this nitrogen is not available.

Should soybeans be innoculated?
You should always innoculate a field that is going to be planted in soybeans if it's been out of soybean production for several years. Especially ground that has been in the Conservation Reserve Program (CRP) needs to be innoculated.

What is the ideal soil pH for soybean plants?
You should target a salt pH-pH rating(s) of 6.1 to 6.5. If using a water pH, pH(w), this will be a rating of 6.6 to 7.0. Soybean plants need this optimum pH range to get proper nodule formation and activity through the rhizobium bacteria.

If the soil test is calling for lime, when should you apply it?
It normally takes lime six to nine months to reach the target pH range. If possible, apply the lime during the summer or fall prior to needing the pH adjusted. When comparing lime quality in Missouri, remember to compare the Effective Neutralizing Material (ENM) value of the lime.

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Planting

What is the optimum row spacing for soybeans?
The primary goal for any crop is a uniform stand without gaps. In general, if weeds are controlled, soybeans will yield more in narrow rows than in traditional row spacings of at least 30 inches. Benefits from narrowing the row width will depend on location, soil conditions, weather conditions, planting date and varieties used.

What is the optimum seeding depth for soybeans?
Adjust planters carefully, depending on soil type and moisture conditions. Normally beans should be planted 1 to 2 inches deep. Never plant deeper than 2.5 inches. Planting seeds too deep can result in lower emergence and poor stands. If planting early in the season in cool wet conditions, plant shallow, about 1 inch.

When is the best time to plant soybeans?
Normally, beans planted during early May have the best yield potential. However, it all depends on the growing conditions at the time they were planted. Just because the calendar says it's time to plant doesn't guarantee that it's the optimum time to plant soybeans. Remember, if the soil conditions are not optimum for planting, don't plant. Normally, soybeans need a minimum soil temperature of 55 to 60 degrees to germinate. A seed that's in the soil but cannot grow will have a higher chance of being exposed to diseases.

What should your plant population be?
Plant population varies depending on row spacing and environmental factors. Normally, you will need a 110,000 to 180,000 final plant population at harvest for adequate stands. This will depend on the row width being used. Planting an excessive population may result in increased lodging. On the other hand, an inadequate stand may lead to more weed problems because of failure to close the canopy. This allows the weeds to compete with the soybean plant for sunlight, moisture and nutrients. Your soil type, location, environment and quality of seed can all influence how many seeds should be planted for a given population.

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Seed Treatments

Weed Control

What weed control program works best for soybeans?
The first thing you need to know before designing a weed control program is the weed spectrum you are trying to control. There are many herbicides on the market. Some have a broad spectrum of control and others have a narrow weed control spectrum. Choose a program that works for you and be sure to scout your fields to see if the program is working. The most expensive treatment is one that does not control weeds. New technology has developed transgenic crops and has made them readily available. Be sure to select the proper seed prior to using a herbicide. There are some excellent choices in herbicides available that may fit into your herbicide program. Chose a herbicide that fits your weed control spectrum.

Should you use a pre-emergent or post-emergent herbicide program?
Pre-emergent programs, post-emergent programs and pre-emergent followed by post-emergent treatments can all be successful herbicide programs as long as the correct herbicide is chosen. All fields are not the same and do not have the same weed spectrum. Choose your herbicides and method of application carefully.

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