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Kansas Soybean
Management 2018
MF3154 Crop Production
How to Use This Guide over several years and sites to provide a better esti-
This publication offers advice to producers, crop mate of genetic potential and stability. A variety that
consultants, and agronomists to manage soybean crops performs well across a range of sites is more likely to
as efficiently and profitably as possible in Kansas. perform well on your farm.
Recommendations provide guidelines and must be
tailored to the diverse conditions found in cropping Planting Practices
systems across the state. Planting date. Soybeans can be planted over a
wide range of dates under good soil moisture avail-
Tillage and Rotations ability, although emergence could be reduced under
Uniform residue distribution, effective weed wet and cool soils (lower than 50 degrees Fahrenheit).
control, proper seed placement, correct planter adjust- The distribution and amount of rainfall during pod
ment, soil testing, and fertilizer management are formation and grain-filling have a large influence in
important for success in conservation-tillage systems. defining yield potential. Under high risk of drought
Crops in a rotation with soybeans usually receive a and heat stresses, diversifying planting dates may be a
benefit compared with continuous monocrop systems. good approach.
Additionally, yields are greater when soybeans Row width. Narrow rows result in equal or greater
are grown in a rotation (e.g. followed by wheat or yields compared to 30-inch rows in conditions with yields
sorghum) vs. continuous monocrop (5 to 10 bushels per greater than 50 bushels per acre (regardless of planting
acre) in a no-till system. Crop rotation also promotes date, seeding rate, or maturity). Benefits of narrow
lower pest pressure. rows include early canopy cover, light capture, weed
control, and reduced erosion. Poor stands can occur more
Variety Selection frequently with narrow row spacing than with wider row
Variety selection should be based on plant traits spacing when a similar seeding rate is used.
such as maturity, lodging, disease resistance, stem Seeding rate. The number of seeds or plants
termination type, iron chlorosis tolerance, and yield per linear foot of row decreases as the row spacing
potential. Varieties adapted to Kansas are generally becomes narrower and increases with the plant
classified as maturity groups III, IV, and V (from density. Late planting dates may require increasing
northwest to southeast). Maturity group III is recom- plant density to compensate for the reduction in the
mended for northern Kansas and under irrigation; length of the growing season. Dry, hot environments
group IV (early and late) performs well in the east require lower optimum plant densities, while favorable
central and southern parts of the state; while maturity environments, such as under irrigation, require greater
group V should be used in southeast Kansas. Stem plant density for capturing greater yield potential.
type termination is related to the growth habit. Planting depth. Optimum planting depth is from
Indeterminate varieties are common for maturity 1 to 1.5 inches. Late planting under dry conditions
groups III and IV, while determinate mostly for group requires deeper seed placement to place the seed in
V varieties or later. contact with moisture. For early planting, place seed
Varieties that stand well under diverse conditions, slightly shallower to shorten the time until emergence
such as irrigation and high fertility and plant density, (related to soil temperature). Soil crusting results in
are preferred to avoid reductions in harvest efficiency. poor stands, exacerbated by deeper seed placement
Look for varieties with resistance to diseases in (deeper than 2 inches), and greater disease pressure.
your area and varieties that perform well over several Inoculation. Planting soybeans without inoculation
locations in Kansas and nearby states. The perfor- in fields out of soybeans for more than 2 to 3 years or
mance of soybean varieties depends on factors such as in Conservation Reserve Program (CRP) land can
weather and management practices. When selecting result in poor nodulation and nitrogen deficiency.
varieties or brands, analyze variety performance for Double cropping. Double-cropped soybeans can
two or more years across locations. When faced with achieve high yields with a similar maturing variety
limited years of data, evaluate performance averaged relative to a full-season crop. Double cropping often
Kansas State University Agricultural Experiment Station and Cooperative Extension Servicebenefits from narrow rows and increasing seeding rates Weed Control
under adequate moisture. Weed control in soybeans was relatively simple for
Calculation of plant density. Soybean seed size several years following the introduction of Roundup
varies among and within the same variety grown under Ready soybeans. Glyphosate was inexpensive and
diverse climatic conditions. Thus, planting rates need generally provided a high level of control of most weed
to be calculated as the total number of seeds per acre. species; so, many producers relied primarily on this
Example: herbicide for nearly a decade. Unfortunately, the heavy
12-inch row reliance on glyphosate has resulted in the development
43,560 sq. ft. /a × × 6 plants/row-foot = 104,544 plants/a
(30) row spacing in inches of glyphosate-resistant weeds. Consequently, producers
Estimation of yields before harvest. Estimate yields at were forced to increase the diversity in their weed
the full pod stage (pods are ¾ inch long on one of the control programs to achieve effective management.
top four nodes), although the precision increases as the The most effective way to manage weeds in
crop is approaching maturity. When estimating yields, soybeans is to use an integrated weed-management
sample a 21-inch row length in several sections of the program that includes crop rotation, good crop
field for one (30-inch row), two (15-inch rows), or production practices, cultural weed-control practices,
four rows (7.5-inch rows). Within that section, count and a diversified herbicide program. A key to plan-
the total number of pods, count the seeds per pod, ning an effective weed-management program is to be
and estimate seed size as related to the conditions in aware of what weed species are present in the field and
that particular growing season. For the seeds per pod have an understanding of the biology of those weeds.
factor, a common average is 2.5 seeds per pod (ranging Annual field records of weed species present, rela-
from 1 to 4). For the seed size, normal to large seed tive abundance, and problem spots are helpful when
weight (2,500 seeds per pound) uses a seed size designing an effective management plan.
conversion factor of 15 units; while for smaller weight Early-emerging weeds are the most competitive
(3,500 seeds per pound) the factor is 21 units. Dry, hot with crops and can be the most difficult to control. It
conditions later in the crop season reduce both seed is important to have a weed-free seedbed at planting.
number and size. Scout more areas to represent natural This can be accomplished with tillage in conventional
variation within a field. tillage systems or with herbicides in no-till. Winter
Example A — Favorable Season: annual weeds generally are not a problem in conven-
264 pods (12 plants × 22 pods/plant) × 2.5 seeds/pod tional tillage because they are controlled with spring
15
= 44 bu/acre tillage before planting. However, winter annual weeds
such as henbit, marestail, mustards, and weedy bromus
Example B — Drought Season (late-drought during
grain-filling period):
Figure 1. Seed moisture dry down (darker line) across
264 pods (12 plants × 22 pods/plant) × 1.5 seeds/pod several soybean genotypes and different nitrogen rates
= 19 bu/acre
21 near Rossville, Kan. Horizontal dashed lines marked the
58 percent seed moisture at black layer formation.
Rate of Dry Down in Soybeans before Harvest 15 days
Soybean dry down rate is three-time faster, 3 September 29 October 14
percent per day, relative to corn at 1 percent per day. For
100 °C day
Seed moisture (%)
58%
soybeans, seed water loss can be divided in two phases: 60
before “black layer” or maturity, and after black layer. 50
During the last days of September and mid-October 40 46%
2016 (Rossville, Kan.), the overall dry down rate was
around 3 percent per day (from 58 percent to 12 percent 30
-0.41X
seed moisture) – taking an overall period of 15 days 20
12%
(Figure 1). These dry down rates for corn and soybeans 10
are primarily affected by temperature, humidity, and
0
-0.03X
overall water content at the point of black layer forma- 0 40 80 120 160 200 240 280
tion (maturity). These main factors should be consid- Thermal Time after black layer (°C day)
ered when the time comes to schedule soybean harvest.
Dry down grain moisture rate, 15 days
46% moisture
Final Estimated Rate ~ 3% drying down per
day after black layer formation
2 K-State Research and Extension | Kansas Soybean Management 2018species that emerge in the fall or early in the spring control postemergence. Preplant and preemergence
can be problematic in no-till systems if not controlled herbicides with good residual pigweed activity are
early enough. Uncontrolled winter annual weeds can critical for their management. The best approach for
use nutrients and moisture, interfere with planting, pigweed control is to use overlapping residual herbi-
and be difficult to control at planting because of their cides as preplant, preemergence and/or postemergence
advanced growth stage. treatments. Relying solely on preplant herbicides too
Fall herbicide treatments from late October early in the spring creates a situation where herbi-
through early December, or early spring treatments in cides will not persist long enough to control later-
March and April can provide good control of winter germinating pigweeds. The primary postemergence
annual weeds and help facilitate better planting condi- herbicides that provide control of the pigweeds in
tions. Herbicide combinations with different modes conventional soybeans are Cobra, Flexstar, Marvel,
of action provide the broadest spectrum of control and Prefix, and Ultra Blazer. All of these products can
help prevent the development of herbicide-resistant provide good control when applied to small pigweeds,
weeds. Glyphosate, 2,4-D, dicamba, metribuzin, but control decreases dramatically after pigweeds
Canopy EX, and Autumn Super are some of the more exceed 3 inches in height, especially Palmer amaranth.
commonly used fall and early-spring burndown treat- Residual herbicides like Zidua, Outlook, Warrant, and
ments in soybeans. Longer residual herbicides also can Dual Magnum can be added to the postemergence
be used in fall and early-spring treatments but tend to applications, but will not control any emerged weeds.
be more costly and not provide much weed control into Where extensive populations of glyphosate-resis-
the soybean-growing season. Consult herbicide labels tant weeds have developed, alternative technologies
for required preplant intervals ahead of soybeans and like Liberty Link or Roundup Ready 2 Xtend soybeans
any guidelines regarding soil texture, soil pH, precipi- may be warranted. These technologies should be used
tation requirements, or geographical use restrictions. as part of a diversified weed management program
Cover crops planted in the fall and then controlled with effective residual herbicides to achieve acceptable
in a timely manner in the spring also may help weed control and sustain the technologies.
suppress weeds. There are many potential cover crop Liberty can provide good broad-spectrum weed
combinations, but to be effective for weed suppression, control with proper timing and application techniques.
they need to establish quickly and be competitive. Liberty works best when applied to small actively
Another key component of using cover crops is to growing weeds and with higher spray volumes and
be able to terminate them effectively and in a timely thorough spray coverage. A second application of
manner to prevent seed production, avoid excessive Liberty 1 to 2 weeks after the first application gener-
moisture use, and facilitate good planting conditions. ally provides the most consistent control.
Summer annual weeds are best managed using a Roundup Ready 2 Xtend soybeans that are resis-
combination of cultural practices (i.e. cover crops and tant to dicamba were fully commercialized for the
narrow soybean rows), residual herbicides as preplant first time in 2017. Xtendimax, Engenia, and Fexapan
or preemergence treatments, and timely postemergence are the only dicamba products labelled for use in
treatments. The most appropriate herbicide program Xtend soybeans. These products have lower volatility
depends on the weed species present and the presence than other dicamba products and have specific use
of herbicide-resistant weed populations. guidelines to minimize the risk of off-target movement
Kochia, giant ragweed, and common ragweed are to susceptible plants, including non-Xtend soybeans.
summer annual weeds that primarily germinate early Even with specific use guidelines, many non-Xtend
in the spring before soybean planting. In addition, few soybeans were injured by off-target dicamba in 2017.
postemergence herbicides are effective for kochia and These products have been classified as restricted use
ragweed control, especially if glyphosate-resistant popu- for 2018 and have even stricter application guidelines
lations are present. Consequently, the key to managing than in 2017. It is critical to follow application guide-
these species is to control them with preplant herbicides. lines, clean sprayers thoroughly, and be diligent with
Conversely, most waterhemp and Palmer dicamba applications to avoid off-target injury.
amaranth do not germinate until later in the spring It is critical to keep accurate records and communi-
and on into the growing season. Waterhemp and cate clearly with your herbicide applicator and neighbors
Palmer amaranth are both pigweed species that can be regarding herbicide-resistant traits within fields to avoid
competitive with soybeans, have developed resistance misapplication and reduce the potential for herbicide
to several different herbicides, and are difficult to drift injury. Flag the Technology is a program that
K-State Research and Extension | Kansas Soybean Management 2018 3consists of different colored and patterned flags to like corn. Banding fertilizer at planting is an efficient
represent different herbicide trait technologies. Flags application method for soybeans. Soybean seeds are
can be purchased online and should be placed at the easily injured by fertilizer, therefore, no direct seed
entrance and/or visible locations in fields for applicator contact with fertilizer is advised.
and neighbor awareness of what traits are planted. Potassium — Soybean seeds are relatively high
Additional herbicide-resistant traits, including in potassium and removal of potassium by soybeans
2,4-D resistant soybeans (Enlist) and HPPD resistant is greater than for other crops on a per-bushel basis
soybeans (Balance GT and MGI) may be introduced when only grain is removed. As with phosphorus, a
in the next couple of years. Most of these soybeans soil test is the best index of potassium needs. Fertilize
will be stacked with more than one herbicide-resistant soils testing very low or low with potassium, either as
trait, but will not be stacked with all of the different a banded starter at planting or broadcast and incorpo-
traits. Regardless of the herbicide-resistant trait, the rated. Potassium should not be placed in contact with
most effective weed control programs are integrated the seed because of possible salt injury. Yield increases
programs with multiple weed-control methods and from potassium can be comparable to those with
diversified herbicide modes of action. phosphorus under very low and low soil test levels.
Sulfur is mobile in the soil (leaching is common)
Fertilizer Requirements but fairly immobile in the plant. High soil test vari-
Compared to corn, wheat, and sorghum, soybeans ability along with significant uptake by crops generates
remove significant amounts of nutrients per bushel of the need for proper sulfur management — especially in
grain harvested. Nutrient uptake in soybeans early in sandier soils and fields with several different soil types.
the season is relatively small; however, as they grow Deficiency symptoms in soybeans are pale-green to
and develop, nutrient uptake increases. Soybeans need yellow leaf color without prominent veins or necrosis
an adequate nutrient supply at each growth stage for in the youngest trifoliate leaves. Recent Kansas studies
optimum growth. suggest a low probability of soybean response to sulfur
High-yielding soybeans remove substantial nutri- application; however, sulfur removal with soybeans can
ents from the soil. This should be taken into account be significant, and more sensitive crops in the rotation
in an overall nutrient management plan. A 40-bushel- such as wheat may require sulfur fertilization after a
per-acre soybean crop removes approximately 30 soybean crop.
pounds of P2O5 and 50 pounds of K 2O with the grain; Iron deficiency symptoms appear in irregularly
in addition, approximately 10 pounds of P2O5 and 40 shaped spots randomly distributed across a field,
pounds of K 2O can be removed with the stover. primarily in fields with a previous history of iron
Nitrogen is supplied to soybeans mainly by deficiency. Different annual weather patterns can
nitrogen fixation. Fertilizer nitrogen application is make iron chlorosis more or less prevalent. Iron
not recommended if the plants are well nodulated. chlorosis also differs under different soil conditions. In
Soybeans are heavy users of nitrogen, removing a total general, high soil pH and high carbonates (free lime)
of 130 pounds per acre and about 44 pounds with the can increase the incidence of iron deficiency. Iron
stover for a 40-bushel-per-acre soybean crop. Soybeans chlorosis can be a big limitation in some regions of
use all the nitrogen they can fix plus nitrogen from the western Kansas. Iron fertilizer using chelated sources
pool of available nitrogen in the soil. Nitrogen fertil- and in direct contact with the seed (in-furrow) has
izer application to soybeans seldom results in any yield shown significant yield responses in soils with history
benefit, and efforts should focus on proper inoculation. of iron chlorosis. If iron chlorosis has been a common
Phosphorus applications should be based on a soil problem in the past, producers should select a soybean
test. Responses to direct phosphorus fertilization is variety tolerant to iron chlorosis. It may be beneficial
generally consistent in soils testing very low or low in to use a chelated iron in-furrow application. Foliar iron
soil test phosphorus. Response to starter phosphorus treatments seldom result in a yield increase.
fertilizer application in soybeans can occur, but it Others — Zinc, manganese, and boron are other
depends on several factors. The most important factor nutrients that can be limiting in soybeans. The need
is the soil test level. Generally, warmer soils at soybean for zinc should be determined by soil tests. Zinc
planting, compared to corn, also may contribute fertilizer can be either banded at or broadcast preplant
to typically lower response to starter fertilizers in with little difference in response when applied at an
soybeans. However, starter fertilizer in soybeans can adequate rate. Both organic and inorganic zinc sources
be a good way to complement nutrients that may have (chelates and nonchelates) can be used, but chelates are
been removed by high-yielding crops in the rotation
4 K-State Research and Extension | Kansas Soybean Management 2018considered more effective than the inorganic sources. best way to manage both diseases. Research shows
Manure applications also are effective at eliminating that soybean cyst nematode is a predisposition agent to
micronutrient deficiency problems, including iron. sudden death syndrome, that is, you rarely see a field
Monitoring nutrient levels with tissue analysis infected with sudden death syndrome that does not
along with soil tests conducted during the crop season already have soybean cyst nematode in it.
should be used to diagnose potential nutrient deficien- A recent 2-year survey indicated that approxi-
cies. Stresses such as drought, heat, and pest pressure mately 20 percent of Kansas soybean fields are
can influence tissue test results. infested with soybean cyst nematode. In two coun-
Nutrient removal by soybean is very high in ties, Cherokee and Doniphan, that number is near
high-yielding environments, so fertilizer application 100 percent. Unfortunately, fewer than 10 percent of
rates will be high or soil test levels will drop. Regular growers indicate they test for soybean cyst nematode.
soil testing (every 2 to 3 years) is essential for optimum While nearly all soybean varieties have some level
nutrient management. Soybeans take advantage of of soybean cyst nematode resistance, recent research
residual phosphorus and potassium, but keep in mind indicates some populations of soybean cyst nematode
the total nutrient needs in the rotation. See K-State are able to overcome the current source of resistance
Research and Extension publication Soil Test Interpre- used in most varieties. Growers should continuously
tations and Fertilizer Recommendations, MF2586 for monitor nematode numbers in infested fields to make
more complete soybean fertilizer recommendations. sure appropriate varieties are being grown. Test all
fields after every third soybean crop to confirm that
Diseases the nematode has not become established, or that it is
Numerous soybean diseases attack soybeans being properly managed.
throughout the growing season. Long-term estimates Recently, seed treatments have become avail-
predict a 12.5 percent increase in soybean yields in able for soybean cyst nematode control, but results
Kansas if diseases could be eliminated. Approximately in university trials has been inconsistent. The use
25 different diseases might occur annually, a much of a newly registered product, ILeVO, has resulted
smaller number are responsible for most disease losses. in significant reduction in losses from sudden death
Early in the season, seed rots and seedling blights syndrome. For more information, see Soybean Cyst
reduce yields an average of 2.5 bushels per acre. The Nematode Management Guide (soybeanresearchinfo.com/
responsible pathogens primarily include Pythium, pdf_docs/SCNGuide_5thEd.pdf ), Scouting for Sudden
Rhizoctonia, and Fusarium, although occasionally Death Syndrome (www.soybeanresearchinfo.com/pdf_docs/
others can be involved. Seed treatment is an effective CPN1012_ScoutingSDS_2016.pdf ), and Sudden Death
means of dealing with seedling blights. Numerous Syndrome (www.soybeanresearchinfo.com/pdf_docs/
products are available that provide good to excellent CPN1011_SuddenDeathSyndrome.pdf )
control of these early-season problems. Use prod- The most significant soybean disease in Kansas
ucts containing two or more active ingredients to is charcoal rot. While this pathogen infects soybean
broaden the spectrum of control. See Soybean Seedling roots early in the season, it does not make itself known
Diseases (www.soybeanresearchinfo.com/pdf_docs/ until the reproductive stages of growth when hot,
Soybean_Seedling_Diseases_CPN1008.pdf ), Soybean dry weather occurs. Under heat and drought stress,
Seed Treatments: Questions that Emerge when Soybean the fungus becomes active and slowly kills the plant.
Plants Don’t (www.soybeanresearchinfo.com/pdf_docs/ Plants that die prematurely typically have smaller
CPN1016._SoybeanSeedTreatments.pdf ) and Fungicide seeds and reduced yields. While all soybean varieties
Efficacy for Control of Soybean Seedling Diseases (www. are susceptible, some are more susceptible than others.
soybeanresearchinfo.com/pdf_docs/BP163W_2017.pdf ). Careful observation of varietal differences can be
General recommendations for seed treatment are useful in management. Also, shorter maturity group
that all fields planted before May 15 should be treated varieties tend to express disease symptoms more
with a fungicide. Use seed treatment in no-till fields at than late-maturity group varieties. Irrigation and
least through May 31. With the expense of high-tech any type of moisture-saving cultural practices can
seeds, many growers are now using seed treatment as reduce disease losses. The most effective management
insurance even on double-cropped soybeans. strategy is to reduce seeding rates to approximately
Two other important diseases, soybean cyst 100,000 seeds per acre. At this rate, there are fewer
nematode and soybean sudden death syndrome, are plants competing for moisture in a dry year. In wet
best managed at planting; resistant varieties are the years, plants still have the ability to branch and
K-State Research and Extension | Kansas Soybean Management 2018 5compensate for fewer plants per acre. See Charcoal Rot Insects
(cropprotectionnetwork.org/soybean/charcoal-rot/). Defoliation of soybeans by insects and mites causes
Kansas has continued to see increases in outbreaks serious concern every year throughout the state. There
of Phytophthora root rot due to soaking rains in early- is a significant difference between full-season vs.
mid-season. Resistant and field-tolerant varieties are double cropped soybeans as far as which pests attack
the best means of management. them, when they attack, and the effect they have. Full-
There are several foliar and late-season stem and season soybeans may be susceptible to wireworms and
pod diseases that reduce soybean yields. These include white grubs early on while double-cropped beans are
frogeye leafspot, brown spot, pod and stem blight, not as likely to be susceptible. All may be defoliated
anthracnose, and Cercospora leaf blight/purple seed by adult bean leaf beetles, webworms, mites, green
stain. Fungicides can be profitable in certain instances, cloverworms, and woollybear caterpillars, but usually
most notably for frogeye leafspot control. Pod and not to the extent that requires treatment. Some of the
stem diseases are tricky to manage because at the time perennial pests in soybeans across the state are:
fungicides need to be applied, it is not apparent as to Wireworms and white grubs may attack the seed
whether or not the diseases are likely to appear. Pod and seedlings of full-season beans, but insecticide seed
and stem diseases are favored by late-season rains. treatments can protect stands for 21 to 28 days.
When a fungicide is necessary, it should be applied Pillbugs are crustaceans, not insects, and therefore
at the R3 to R5 growth stage for maximum effective- require a moist environment to be able to get oxygen
ness. Growers should be cautious about overuse of through their gills (Figure 2). Populations only obtain
strobilurin fungicides. Strobilurin-resistant frogeye densities sufficient to reduce soybean stands in no-till
leafspot has already been reported in 11 states; fortu- fields. They have been serious pests in south central
nately, Kansas is not yet one of them. See Fungicide Kansas because they bite off the small, succulent seed-
Efficacy for Control of Soybean Foliar Diseases (www. lings, causing stand losses. Insecticide seed treatments
soybeanresearchinfo.com/pdf_docs/Fungicide_efficacy_ are not effective and foliar applications only work if
BP161W_2017.pdf ). there is no residue to block the spray from contacting
Soybean rust has only occurred once in Kansas, the pillbugs.
in 2007, since its introduction into the United States Bean leaf beetles have historically been a serious
in 2004. Each year, its spread is tracked through a pest of soybeans throughout all soybean-producing
national reporting network (ext.ipipe.org/ipipePublic/ regions (Figure 3). Adults can defoliate early-season
index.php#tags=Soybean). Should it threaten Kansas in plants by chewing round and/or oval holes in leaves.
the future, numerous outlets will update growers as to Females then oviposit in the soil around the base of
the need for fungicide usage. plants where the white larvae feed on roots. Emerging
All other diseases, including bacterial blight, downy adults feed on leaves but also may feed on green pods,
mildew, aerial blight, Sclerotinia white mold, stem which can cause yield loss relatively quickly. Foliar
canker, bean pod mottle virus, bud blight, and soybean insecticide applications usually work well to control
vein necrosis virus occur too infrequently to warrant bean leaf beetle adults and prevent this pod feeding.
control or there are no effective control measures. Soybean podworms are called corn earworms in
corn. Adults fly from corn to soybeans where females
oviposit on leaves and larvae often feed on seeds
through the pod. Adult bean leaf beetles feed on the
pods whereas podworms chew through the pods to feed
on the seeds within. Early detection, while the larvae
Figure 2. Pillbug feeding damage on seedling soybean plant. Figure 3. Both color forms of the bean leaf beetle and
characteristic round foliar feeding damage.
6 K-State Research and Extension | Kansas Soybean Management 2018are still small, is the key to good control. Ensure proper Kansas where more than 60 percent of irrigated
identification of larvae as other worms commonly soybean production occurs. The top ten counties in
found in soybeans do not feed on seeds. Small, hair-like irrigated soybean production are within the bound-
microspines on podworms are the key to identification. aries of groundwater management districts 2 and 5.
Green cloverworms again caused significant Soybeans are a relatively drought-tolerant crop, but
defoliation, much like 2016. respond well to irrigation. In 2009, the last year of
Thistle caterpillars were also abundant and irrigated soybean yield information, irrigated soybeans
actually completed two generations in Kansas soybean averaged 59 bushels per acre statewide as compared
fields. Amazing numbers of painted lady butterflies to 42 bushels per acre for dryland soybeans. Irrigated
emerged from the last generation and headed south to soybean yields were increasing at a rate of about
overwinter. 0.57 bushels per acre per year from 1984 to 2009 as
Stinkbugs may insert sucking mouthparts into compared to 0.36 bushels per acre per year for dryland
soft, succulent seeds as they develop inside pods. This production. Figure 4 shows the average yield of the top
can result in shrunken seeds with wrinkled coats and five entries at various Kansas State University soybean
30 to 50 percent yield loss. performance trials across Kansas from 2008 to 2017.
Soybean aphids have continuously migrated into Two eastern counties also had dryland plots but at
Kansas since they were first detected in 2002. These different sites than the irrigated sites.
aphids rarely reach infestation levels that warrant
insecticide applications, but that potential is always Plant Characteristics
present for these prolific pests. Ants in soybean Soybeans are a relatively deep-rooted crop. In deep,
canopies indicate aphid infestations are present. well-drained soils with no restricting layers, roots can
Dectes stem borers continue to be problematic penetrate to 6 feet. As with all crops, most of the roots
throughout the western two thirds of Kansas. Yield are concentrated in the upper half of the root zone.
losses from this insect’s habit of girdling around the Managing a root zone of 3 feet is the general irrigation
inside of the stem before harvest can be minimized by recommendation. Water use requirements, also known
harvesting infested fields as early as possible. as evapotranspiration or ET, for soybeans range from 17
Refer to K-State Research and Extension publica- to 28 inches depending on climatic conditions.
tions Soybean Insect Management, MF743, available Water use is generally slightly higher in the west
online: www.bookstore.ksre.ksu.edu/pubs/MF743.pdf than the east. A value around 22 inches is a good
and Crop Insects of Kansas (S152) for more in-depth average estimate for the state. Daily water use varies
descriptions of soybean pests, damage, and manage- with the stage of growth and weather conditions. The
ment recommendations. typical peak water use rate is about 0.35 inch per day
as typical for all summer-grown field crops, which
Irrigation normally occurs near the beginning of the pod fill stage
In 2014, more than 450,000 of the 3 million (Figure 5). Single-day peak water use rates can approach
irrigated acres in Kansas are soybean. Approximately 0.5 inch per day. Water use is low at the germination
10 percent of the harvested soybean acres are irrigated. and seedling stages, peaks at or near the full-bloom
Irrigated soybean production is concentrated in the stage, and then declines with maturity. The most
central third of Kansas; particularly in south central critical time for adequate soil water availability is during
the end of the reproductive period when pod fill begins.
Figure 4. Soybean yield (bu/a) for the top 5 entries of various
Soybeans produce many flowers relative to the final
K-State performance trials across Kansas (2008 - 2017).
Figure 5. Soybean water use or daily evapotranspiration (ET)
from a well-watered crop (Nebguide 1367 UNL).
Average Yield of Top
Five Entries (bu/a)
0.7
Vegetative Stages Reproductive Stages
0.6
Germination Rapid Flower Pod Dev. Seed Maturation
Estimated Soybean ET (in/day)
and Vegetative R1-R2 R3-R4 Fill R7-R8
0.5 Emergence Growth R5-R6
0.4
0.3
Long-term
0.2 Average ET
Shawnee Republic Reno Thomas Finney 0.1 Actual ET
County County County County County
Location of Performance Trial 0.0
4/24 5/24 6/23 7/23 8/22 9/21 10/21
Dryland Day of the Year (month/day)
K-State Research and Extension | Kansas Soybean Management 2018 7number of pods, so losing a few flowers to light water to non-irrigated. Yield also increased as the number of
stress earlier in the reproductive cycle is not as critical irrigations increased; however, the maximum yield of
to final productivity as the same water stress during the trial occurred using a 50 percent depletion criterion
pod fill. Net irrigation requirements for soybeans in dry (52 bushels per acre), which used less water than the
years range from around 14 inches in western Kansas three-application treatment (51 bushels per acre).
to less than 5 inches in the east. Requirements in an This enforces that irrigation scheduled by using
average year will be 2 to 4 inches less. planned depletion is a best management practice.
Research studies across Kansas and throughout Irrigation scheduling in this form can be accom-
the High Plains confirm that the most beneficial plished using either soil water measurement devices
timing for a limited amount of irrigation is during the or climatic-based (also known as evapotranspiration-
latter part of the reproductive growth stages rather based) irrigation scheduling. This latter method can
than earlier. This is generally true because early-season be accomplished by using the K-State Research and
growth and development can be satisfied by typical Extension KanSched irrigation scheduling program;
rainfall and stored soil water. When full irrigation is available at www.bae.ksu.edu/mobileirrigationlab/ along
possible, a managed allowable depletion level of 50 with other free irrigation decision support software.
percent in the managed root zone is the recommended
management guideline; the typical managed allowable Crop Rotation
depletion for most field crops. Since soybeans do not The potential benefit of crop rotation may be a
have an extremely critical stage of growth, they also do consideration. From an irrigation standpoint, irriga-
well under deficit irrigation. The peak water use rate tors with limited irrigation water capacity usually find
is generally later in the season than corn, which means soybeans complement corn irrigation when water can
soybeans may be used as a field acreage split with corn be shared between fields or the two crops split acreage
as a way to reduce water stress potential at the critical within a field since soybean critical water period is
growth stage of corn at tasseling. usually later in the season versus the earlier critical
Research results from the K-State Research Experi- tasseling period for corn. Soybeans also can be used as
mental Field at Scandia, Kansas, illustrate scheduling a late-season double crop with wheat.
by soil water depletion (30 or 60 percent), which did
not limit the total season application amount, uses less Irrigation Summarized
water to provide similar yields (53 vs. 52 bushels per Soybeans are a good irrigated crop option with
acre). The 30 percent depletion also occasionally had great yield potential for both full and limited irrigation
increased lodging. In some years, 60 percent deple- regimes. Peak daily water use rates are about 0.35 inch
tion had only one irrigation application. For the 2011 per day with seasonal water needs ranging from 17 to
soybean season at Scandia (rainfall was 8.3 inches below 28 inches. When limited water is available, late-season
the 30-year average), a strong yield increase was docu- irrigation is generally most important.
mented from single in-season irrigation as compared
Ignacio A. Ciampitti Dorivar Ruiz Diaz Douglas J. Jardine
Agronomy Agronomy Plant Pathology
Crop Production and Cropping Systems Soil Fertility and Nutrient Management Field Crop Diseases
Dallas E. Peterson R. Jeff Whitworth Danny H. Rogers
Agronomy Entomology Agricultural Engineer
Weed Science Integrated Pest Management Irrigation
Douglas E. Shoup
Southeast Area
Crops and Soils Specialist
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is intended, nor is criticism implied of similar products not mentioned.
Publications from Kansas State University are available at: www.bookstore.ksre.ksu.edu
Contents of this publication may be freely reproduced for educational purposes. All other rights reserved. In each case,
credit Ignacio A. Ciampitti et al., Kansas Soybean Management 2018, Kansas State University, January 2018.
Kansas State University Agricultural Experiment Station and Cooperative Extension Service
MF3154 January 2018
K-State Research and Extension is an equal opportunity provider and employer. Issued in furtherance of Cooperative Extension Work, Acts of May 8 and June
30, 1914, as amended. Kansas State University, County Extension Councils, Extension Districts, and United States Department of Agriculture Cooperating,
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