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Soybean Production


Soybean Frost Damage

Research information from Wisconsin has shown that all varieties tested had reduced yields when frost occurred at or before R6. Earlier-maturing varieties sustained economic yield losses from frost at more advanced growth stages than later-maturing varieties. The greatest yield losses occurred when frost occurred at stage R5. The number of beans per plant and reduced bean size contributed to overall yield loss. Maturity was hastened by some frost treatments and was not delayed in any of the trials studied.

Table 1.  Maturity rating of soybean.

R5                Beginning seed - Seed 1/8 inch long in a pod at one of the four uppermost nodes on the main stem with a fully developed leaf.

R6                Full seed - Pod containing a green seed that fills the pod cavity at one of the four uppermost nodes on the main stem with a fully developed leaf.

R7                Beginning maturity - One normal pod on the main stem that has reached its mature pod color.

R8                Full maturity - Ninety-five percent of the pods have reached their mature pod color. Five to 10 days of drying weather are required after R8 for the soybean moisture levels to be reduced to less than 15 percent.

Soybean seed on frost-damaged plants many mature and change color as early as or even earlier than nonfrosted soybean plants. The leaves tend to remain on the frost-damaged soybean plants. Seed moisture may be slightly higher and seed size usually is reduced as the soybeans dry and shrink. A frost will not hurt soybean yields if the soybean growth stage is beyond R7. A frost between R6 and R7 may or may not affect yield, depending on the temperature and duration of the freeze.

Beans that are still green and soft will shrivel. Stalks rapidly turn dark green to brown and will not recover. Beans in pods that have turned yellow will mature normally. Some green beans will turn yellow after 30 to 40 days of storage.

Growers and researchers through the years have tried to use color keys such as yellow soybean leaves, yellow pods and brown pods to estimate soybean maturity and safety from frost. Generally these methods didn’t work because of differences in varieties regarding symptoms of maturity. However, studies do show that “yellow” pods sprinkled with brown are the best clue of physiological maturity.

Open pods and check shrinking of beans and look for separation of beans from the white membrane inside the pod. This indicates the soybean plants are physiological mature and fairly safe from frost injury. Pods do not all mature evenly. Note that if one or two pods on any of the upper four nodes have turned brown and other pods are light yellow to tan, the soybean plants are fairly tolerant to a killing frost. In the event of a leaf-killing frost when pods are still light green or yellow, wait until the pods are mature in color before combining. The most significant effect of an early frost on soybean may be in the reduction in their value as a future source of seed.

Generally speaking, soybean fields planted to narrow row spacings (6 or 7 to 12 inches) may have slightly more tolerance to light frosts than soybean planted in wider rows (30 to 36 inches). The heavy plant canopy of the solid-seeded, closely drilled beans tends to hold the soil heat better and therefore protects the plants to some degree.

Table 2. Percent of Yield Produced by Various Soybean Growth Stages

Growth Stage Yield

Days After Bloom Begins

Days to Maturity

Percent of Total

Begin pod




Full pod




Begin seed




Full seed




Begin maturity




Full maturity




-Source: University of MN  reported at

If all leaves on a soybean plant are killed between full seed stage and beginning maturity, 53% or less of yield can be lost. A freeze before maturity has less effect on yield the closer the freeze date is to mature date.

Air temperatures of 29 degrees F are necessary to completely kill soybean plants.

Quality Factors of Green Frosted Soybeans

Every year the question surfaces of what to do about green soybeans and/or green soybean oil. The frost of Sept 15, 2011 makes the concern greater than usual.

The green color comes from chlorophyll or chlorophyll-like compounds and relates to immaturity of the harvested soybeans. If harvested soybeans are compared to normal soybeans, the greenish color is quite apparent visually.

If the soybeans are only slightly green, there is a good possibility that drying and storage will fade out the green. On the other hand, slightly green soybeans give the refiner the most problems because the green color in the oil may be masked by the red and yellow. During normal processing the red and yellows are reduced and the greens then may become apparent and are, of course, undesirable.

There are discounts for green soybeans and these stem from the refining problems stated above. If soybeans do not lose the green color in storage, then soybeans destined for extraction will inevitably be discounted.

Other alternatives than extraction such as utilization as full-fat soybean meal either by roasting or extrusion should be considered to avoid discounts. The green color should have no impact on feeding values if the soybeans are normal in composition otherwise.

Source: American Soybean Association, August 1992.  Reported at

Green Soybeans Can Be Used for Livestock Diets

Although frost-damaged or green soybeans are likely to be rejected by processors, they can be used in livestock diets.

The green pigment, or chlorophyll, remains in the oil and in the meal, making them undesirable to processors, but it doesn't matter at all to livestock.

Research at South Dakota State University indicates raw, frost-damaged soybeans should be limited to less than 14 percent of the diet dry matter to avoid negative effects from the amount of oil or enzyme inhibitors present in the raw soybeans. In the research, lambs fed higher levels of soybeans in corn-silage based diets had lower fiber digestibility because of the high oil levels.

Whole soybeans are high in oil content, about 18 percent, which will limit the amount a producer can include in ruminant rations. Fat or oil tends to reduce fiber digestibility and animal performance when fed at high levels. Keeping the level of whole soybeans less than 14 percent of the ration should be adequate to avoid any problems associated with fat level in the diet. As a general rule, keep added fat in ruminant diets from any oilseed below 2.5 to 3 percent.

Although whole soybeans do not need to be ground or rolled before feeding them to cattle or sheep, processing them in some way may make feed mixing easier and prevent livestock from sorting through feeds. In warm weather, only process the amount which will be fed in seven to 10 days, since warm temperatures can cause the processed beans to become rancid.

A laboratory test will help determine the nutrient content of frost-damaged soybeans. The biggest challenge in feeding damaged crops is the variability in nutrient content. A test will help you formulate a more accurate ration.

Reported at


July 6, 2011

Days will get shorter after June 21. The lengthening of the nights is a trigger point for the soybean plant to change from the vegetative to the reproductive phase of plant growth. In the first week of July we can start to see the first flowers on early maturity group soybean plants. Crop plants require heat to develop, grow, and mature. The effect of this heat is cumulative as the growing plant progresses through its life cycle. In North Dakota, Growing Degree Day (GDD) Models have been developed for barley, canola, corn, sugarbeet, sunflower and wheat (

A model to predict the growth and development for soybean is not yet available. Soybean varieties are adapted within a narrow north-south geographical zone mainly because the plant is photoperiod sensitive. The dates of flowering and maturity in soybean varieties are important to determine their geographical adaptation.

We analyzed growth stage data recorded during 2004, 2005, 2006 and 2007 growing season at Carrington Research Center (Endres et al.). The data contained soybean growth stages starting from VE to R8 for two different maturity groups: 0.0 and 0.4. We calculated the accumulated GDDs corresponding to the end of each growth stage using the NDAWN GDD (based 50°F) application.

Based on these preliminary results we concluded that:

Growth stage is reliably predictable up to R1 stage. From R1 to R8, range of GDD estimating soybean growth stage widens. For example the lowest and highest GDDs predicting R2 was 891 (in 2006) and 1052 (in 2005) respectively. The difference in GDDs was 161°. This range was even higher for R8. We will continue to investigate the relationship between GGD and developmental stages of the soybean plant.


As the soybeans are starting to develop and the true leaves appear (V1-V3) yellowing of the plant is sometimes observed. The problem most likely is a deficiency of iron (Fe) in the plant. Shortage of Fe can cause a reduction of chlorophyll production showing up as yellowing of the leaves. Iron Deficiency Chlorosis (IDC) is expressed in new leaf tissue as an interveinal yellowing while the veins remain green.  As the deficiency progresses, leaf tissue and even the growing point can die.  Iron is an essential micronutrient for the plant. Besides being needed in chlorophyll, Fe is also involved in the energy transfer of the plant, is part of certain enzymes, and is needed in the root nodule formation associated the N-fixation.

The effect of IDC is reduced plant growth and can lead to a reduction in yield potential.  Even a temporary yellowing is associated with yield loss. Usually there is abundant iron in the soil in North Dakota and only a small amount is needed by the plant. Iron is rather insoluble and with increased soil pH the solubility becomes even lower. Soils with calcium carbonate (lime) in the topsoil are most prone to produce soybeans with IDC.  However, increased salt concentration, wet conditions, cool temperatures and readily available nitrate near the plant can all interact and aggravate the IDC symptoms.  Compared with other crops soybeans are inefficient in using Fe.  If the deficiency is not too severe, soybeans can grow out of IDC as the conditions improve and the larger root system is able to take up sufficient Fe.

There is a difference in how soybean varieties respond to adverse conditions. In soils with poor drainage, high pH, and salinity issues farmers should have selected the most tolerant soybean varieties available for the maturity zone.  As the crop is already growing and the variety cannot be changed at this time, it would be a good strategy to note which fields show elevated IDC levels and see what the NDSU (IDC) rating is on the presently grown variety. If IDC is an issue, varieties selection based on IDC ratings should be considered in future plantings.  IDC scores for varieties can be found in the NDSU Soybean performance testing results publication A-843 or at

None of the presently grown commercial varieties are completely tolerant against IDC but there are definitely big differences among varieties in their response to IDC. Variety selection is the most important management decision to combat IDC in soybean. Improving internal soil drainage and leaching out of salt may also help to create more favorable growing conditions in future years.

Foliar application of Fe might be an option to consider. Re-greening of the plants is possible and depends on the variety and especially the timing of the application. Early application, even at the first trifoliate growth stage, can be considered. If application is delayed and the symptoms are severe, spraying may not be as effective.  Based on research conducted by Dr. Rehm in Minnesota the results of foliar application of Fe are inconsistent. The cost of the product, application cost, and potential wheel damage due to driving in the crop should be considered when thinking about a foliar application.  If the soybeans are grown in wider rows, 1 or 2 lb/a of FeEDDHA can be applied, with the spray focused narrowly on the rows.  If washed off by subsequent rains, the FeEDDHA has soil activity, unlike most other foliar materials.  However, it is better to prevent chlorosis by planting a resistant variety and using FeEDDHA as a starter fertilizer, than to try to green up a crop after it has turned yellow.

Hans Kandel - Extension Agronomist Broadleaf Crops

Jay R. Goos - NDSU Soil Scientist



In 2013, soybean will continue to be the most common broadleaf field crop grown in North Dakota. Farmers are interested in the combination of production management strategies to economically improve soybean yields. North Dakota State University is conducting several research trials to assist with this goal.

A soybean intensive management study has been conducted since 2008 to examine combinations of planting rates, row spacing, and special foliar inputs using early and late-maturing varieties to identify the most profitable combination. Best management practices are used in the study including seed inoculation, and seed treatment with a fungicide and insecticide. Six site-years of data have been generated from trial locations at Carrington and Prosper. The research is being supported by the North Dakota Soybean Council.

Planting rates of 150,000 and 200,000 pure live seeds (PLS) per acre have been compared, resulting in an average established stand of 138, 000 and 175,000 plants per acre, respectively. NDSU currently recommends an established soybean stand of 150,000 plants per acre, with variance of 10 percent, to maximize yield potential.  Results from the study indicates a yield advantage of just under 1 bushel per acre or a yield increase of 1.5 percent averaged across site-years for the high planting rate. However, when costs and benefits are calculated the lower planting rate is more economical.

Fourteen-inch row spacing has averaged 1.1 bushels per acre or about 2 percent greater yield than using 28-inch rows.  This confirms other university data indicating a higher yield potential with intermediate rows versus wide rows. Also in the NDSU study, canopy closure occurred an average of about a month earlier with the 14-inch compared to wider 28-inch rows. Quicker canopy closure provides advantages including greater weed competition, soil moisture conservation, and increased capture of sunlight, all potentially resulting in higher yield using the narrower rows.

Special foliar inputs, including a nutrient combination plus a growth promoter were applied at the early vegetative stage. This was followed by a fungicide application during the flowering to early-pod formation stages. Across site-years, the special inputs increased soybean yield 2.2 bushels per acre or about 4 percent, compared with the untreated check. However, there was only a modest return-on-investment. The study results indicate the combination of planting 150,000 PLS/acre in 14-inch rows followed by the combination of special foliar inputs provides the highest return on investment among options explored in the study.

In another on-going study conducted at Carrington to examine special inputs for soybean, numerous individual products or combinations applied at various plant stages have not consistently provided yield gain or economic returns. Producers should use caution when considering additional inputs beyond management practices recommended based on university research.

Greg Endres - Extension area agronomist at the Carrington Research Extension Center

Hans Kandel Extension Agronomist Broadleaf Crops

Soybean plant stand

Replant decisions should only be made after taking stand counts to determine plant populations as visual observations tend to underestimate the plant population. Narrow row width may exaggerate the impression of low plant stand because there are larger spaces between plants within rows. Replanting is not recommended unless the cause of the previous poor stand can be corrected. Factors to consider when evaluating a stand include: why was the stand reduced (water saturated areas, shallow seeding, planter plugged), how uniform is the remaining stand, what is it’s yield potential, what is the weather forecast for the coming period, is there still enough time to replant (consider maturity of the soybean), and what is the cost of replanting (machinery, seed and labor).

Usually the stand reduction is not uniform throughout the field. Loss of stand is frequently irregular. Gaps may occur in rows, but if the gap is less than 2 feet in diameter, the adjacent soybean plants are capable of developing branches to occupy the space. Plants can adjust to low populations by producing more branches per plant, by increasing the number of pods both on the main stem and branches, increase the number of seeds per pod, or increase seed size. Open spaces more than 2 feet in diameter may lead to reduction in yield.

To determine plant stand, select the area of the field with lowest plant stand and compare with the normal plant stand in other parts of the field. Make at least 10 random stand counts in an area where the stand is reasonably uniform. Use a tape measure and mark off 1/1,000 of an acre for each count. The lengths of rows equal 1/1,000 of an acre with different row widths is indicated in Table 1. Multiply stand count per length of row by 1,000 to obtain stand per acre. NDSU’s recommendation is 150,000 established plants per acre.

Table 1. Length of row to equal approximately 1/1,000 of an acre

Row With in inch

Length of row to equal 1/1,000 of an acre


17 feet and 5 inches


26 feet and 2 inches


34 feet and 10 inches


52 feet and 3 inches


74 feet  and 9 inches

Soybean populations can vary perhaps as much as 50 percent from recommended levels without affecting yields, as long as missing gaps are not too large and weeds are controlled. In summary: before even considering re-seeding count the stand and calculate the cost.

For more information see: The Soybean Growers Field Guide for Evaluating Crop Damage and Replant Options



Minimum Soybean Stands

Hans Kandel, Extension Agronomist

Based on research and hail loss studies, the minimum stand for soybean is suggested to be around 75,000 plants per acre, which is approximately 50% of the recommended stand. If you use the “hula hoop” method of determining stand counts in solid seeded fields, you would need a minimum of 1.7 plants per square foot.  With a 50% stand loss, yield reduction will be somewhere between 10-20% of the anticipated yield of timely planted soybean. However, soybean stands will not always be uniform throughout the field, there will be places here and there with higher or lower plant counts. These uneven gaps between plants can potentially result in even lower yields, depending on how many gaps there are or the distance of spacings between the plants. Soybeans have the ability to compensate for low populations by additional branching, setting more pods per plant and filling more seeds per pod. The plants in low population environments may have lower branches that might break before or during harvest thus increasing the potential for greater harvest losses. Also some of the pods will develop lower on the plant. Extra care and efforts during harvesting can reduce this harvest loss problem. It is often a difficult decision whether to let a low population crop develop or to re-plant. Some producers have asked about seeding extra soybeans into the uneven or thin stand. In the case of poor stand establishment, replanting alongside the established seedlings, to patch up or thicken the existing stand, seldom improves yields. Repair planting often leads to timing difficulties with crop management like weed control and harvest date. When dealing with unacceptably low stands, significant yield improvement will be best achieved when the original soybean stand is so poor that it needs to be destroyed and a new stand re-established. However, it is advised to replant with an earlier maturing variety to compensate for the shorter growing season left before the first fall frost. Producers also need to be aware that there is an additional cost to buy seed, work the land, and plant the seed. The yield potential of the later planted soybean will be lower when compared with timely planted soybeans


NDSU Soybean Disease Information for the Region

Natto Bean Soybean Report 2008

How a Soybean Plant Develops

Soybean Soil Fertility

Soybean Production Field Guide

Brazil Soybean Production

Diseases and Soybean Rust Information

Soybean Growth and Management Quick Guide

Iron Chlorosis Tolerance Information


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