Soybean Planting Date and Varietal Maturity

Along with the continuing emphasis on getting soybean planted early – in late April to early May – comes the question of soybean maturity rating, and whether early planting benefits fuller- or shorter-season varieties the most.

Planting date

Figure 1 was updated with the 2014 data from our planting date trials in central and northern Illinois. The change compared to the response I showed a year ago is mostly from the large response to delayed planting at Urbana in 2014. Here, the April 23 planting yielded 95 bushels per acre, and yields dropped as a straight line (rather than the usual accelerating loss), losing a little more than a half bushel per day of delay, to only 66 bushels per acre planted on June 15. That dragged down the line some, with accumulated losses of about 5 and 16% by the end of April and end of May, respectively. There is a lot of spread of data at different dates, so we know that actual losses won’t hit the line on the graph most of the time.

Figure 1. Soybean planting date response over 19 central and northern Illinois site-years, 2010-2014.

Varietal maturity

Jake Vossenkemper, a PhD student working with me, has been doing research to see how planting date affects yields of soybean varieties that differ in maturity. The first question is whether varietal maturity has a consistent effect on yield by itself. Data from the central Illinois region of the UI variety trials over the past 15 years shows that this effect is not very consistent – yields of later-maturing varieties can be higher or lower than those of early-maturing ones depending on the year (Figure 2). On average, though, mid-maturity varieties tend to yield slightly more than either early or late varieties, and those within a bushel of the top-yielding maturity covered a spread of about one half of a maturity group on either side of the highest-yielding group  (Figure 2). It is also clear that yields are much more closely tied to genetic potential than they are to maturity itself, even though on average varieties with very early or very late maturity tend to yield less.

Figure 2. Soybean yield as affected by varietal maturity in UI variety trials in the central Illinois region (3 sites) over 15 years, 2000-2014. Four years were selected to show contrasting effects, and the yellow line is fit to the data over all 15 years.

Planting date and varietal maturity: do they interact?

We can see in Figure 2 that the type of growing season can have a considerable effect on how yields are affected by maturity. But how does this work when planting dates are different within a growing season? To address this question we have run a series of trials using a range of varietal maturities over a number of sites in different regions over recent years. Trends in different regions were similar, but we’ll show here the large data set (12 site-years) from central and northern Illinois and one site in Iowa. Varietal maturity ranged from about 1.9 to 3.8 with the baseline at about 2.9 in the northern sites, and from 2.5 to 4.5 with the baseline at about 3.5 in the central sites.

With early (late April to early May) planting, yields across the 12 site-years were maximized at a maturity that was about 0.4 units later than the mid-maturity baseline, and yields were within a bushel of the maximum (of about 74 bushels per acre) over maturities ranging from the baseline to about 0.8 units above the baseline, or about 0.4 units on either side of the maximum (Figure 3).  When planting was at the normal time of mid-May, the maximum yield dropped to about 66 bushels, or 7 to 8 bushels lower than the maximum with early planting, in line with the expectation based on planting date (Figure 1). At the later planting, varieties with a maturity close to the baseline maturity yielded the most, and the range of maturities that yielded within a bushel of the maximum was slightly wider than with early planting, ranging from about 0.5 units below to 0.5 units above the maximum (Figure 3).

Figure 3. Interaction between varietal maturity and planting date across 12 site-years in central and northern Illinois and central Iowa, 2012-2014. The green circles are at the highest point on each curve and the red triangles indicate the ends of the ranges over which yields are within 1 bushel/acre of the maximum.

Do we see enough here to try to tailor the maturity we use for planting at different times? Probably not in terms of changing maturity on the fly as planting time approaches – the decision on best-performing varieties has to be made before then, and if made with care should be solid enough to stand regardless of planting date. But if you have fields where early planting is often possible, you might “shade” towards a little longer maturities for those, and if there are fields that often stay wet until past mid-May, choosing from among adapted mid-season varieties makes sense. There seems to some advantage in choosing to plant fuller-season varieties earlier rather than later, though that strategy tends to work against the goal of using different maturities to spread harvest.

Emerson Nafziger and Jake Vossenkemper

Soybeans and Nitrogen Fertilizer-Again

In April 2014 I wrote on the topic on N fertilizer on soybeans, reporting that our research at the University of Illinois has rarely shown a benefit in yield to applying N fertilizer during the middle part of the season. But it seems that some people, perhaps reacting to testimonials of high yields after using N fertilizer in the high-yield conditions of 2014 remain convinced that adding N fertilizer “makes high yields higher.”

Of course, most producers who got high yields – 20 Illinois counties averaged 60 bushels per acre or more in 2014, with Piatt County reporting an average of 69.2 – did so without using N fertilizer. But the idea that soybeans can’t produce high yields and at the same time fix all of the N that they don’t get from the soil is apparently a compelling one, even though it lacks much supporting evidence.

Our Illinois results

We continued a small amount of work on N on soybeans in 2014, and Figure 1 summarizes the results of 33 comparisons we have run over the past five years. In these trials the N has been applied as urea, urea with urease inhibitor (Agrotain®), and/or polymer-coated urea (ESN) that slows release. Rates have ranged from 100 to more than 300 lb of urea (45 to 150 lb of N) per acre, and applications have been made between first flower (R1) and R4, or full pod stages. I included results from a study where N was both added to untreated plots and where N was left out of a “package” of practices considered to be helpful to high yields.

Figure 1. Soybean yield and response to fertilizer N in 33 Illinois trials, 2010-2014. Green symbols indicate that the response was statistically significant (likely due to treatment and not to chance.)

Yields ranged from 39 to 87 bushels per acre, with an average of 66. We saw significant (statistically likely to have been due to treatment, not just to chance) yield increases in two of the 33 trials, both about 6 bushels above the untreated check, and a significant decrease (of a little less than 5 bushels) in one trial. The average response to using N fertilizer over all 33 trials was a half bushel (increase) per acre. There was no tendency for the response to be higher in higher-yielding trial; the ten lowest-yielding sites showed an average response of about one bushel while the 10 highest-yielding sites showed an average response of only a quarter of a bushel.

These results show that adding N fertilizer can increase soybean yield, but that also that a consistent yield increase is not likely. Getting a yield increase high enough to pay for the practice is also unlikely. The cost of the fertilizer (100 lb of urea is about $23 at the current price of about $460 per ton) plus application means that yields need so increase by 3 to 4 bushels per acre just to break even. Ignoring statistical significance, we saw a yield increase of 3 bushels or more in five of the 33 trials and of 4 bushels or more only three times.

Getting to a real-world answer

The need to find out how often and by how much fertilizer N affects soybean yields provides a perfect opportunity for Illinois farmers and fertilizer retailers and applicators to cooperate in running on-farm strip trials. I included the how-to in an article last spring, but there weren’t many takers. We don’t have funding for this, but I would like to think that there is a group of people willing to cover the costs to make this work. I’m certainly willing to do my part, also without funding. In my vision of the future, this is how agronomic decisions will be made.

Laying out a trial like one to test N fertilizer on soybean is reasonably simple:

    • Find a uniform part of a field large enough to accommodate 12 strips wide enough to apply N fertilizer to, and large enough to get accurate harvest yields with the combine. Unless N can be dropped very precisely to strips exactly as wide as the combine will harvest, N strips will need to be wider than the combine. They should be long enough to get a good yield estimate, whether that’s with a yield monitor or a weigh wagon. Record (GPS) coordinates along with soil type, previous crop and its yield, planting date, seeding rate, variety, herbicides, application date, harvest date, and anything else that you think might have affected the crop or the response.
    • Assign treatments to strips randomly within each pair of strips. Here is how this might look:
      Strip 1 No N
      Strip 2 +N
      Strip 3 +N
      Strip 4 No N
      Strip 5 +N
      Strip 6 No N
      Strip 7 No N
      Strip 8 +N
      Strip 9 No N
      Strip 10 +N
      Strip 11 +N
      Strip 12 No N
        • Apply in-season N to the strips where it was assigned. Timing and form are not fixed, but most will want to use 45 to 90 lb of actual N (100 to 200 lb of urea, possibly including a urease inhibitor; ammonium nitrate at a similar N rate is also an option) applied between stage R2 (full flower) and R4 (full pod). Injected UAN or anhydrous ammonia can also be used if crop size and row spacing allow. If you run over plants to apply by ground, you’ll want to drive (with applicator off) down the “No N” strips as well so all strips experience the same degree of damage. With aerial application, strips will need to be wide enough so fertilizer doesn’t fall into no-N strips. Make certain, either with GPS or with flags (PVC lengths installed using a soil probe work well and are visible), that you know exactly where the N went on and where it didn’t, so you can harvest correctly.
        • Harvest and record yields for each strip. Be sure that the width harvested is the same for each strip, and trim the ends after harvest if using yield monitor data. An increasing number of acres are being harvested at an angle to row direction these days, and that won’t work for these trials unless N can be applied at the same angle.
        • I’m willing to receive data from trials like this and to send back yield averages after doing stats. If you or an adviser analyze your own, I’d much appreciate getting the data so we can look at this across all sites.

        This addresses an important question, and one that will be answered adequately only with on-farm trials like this. It’s especially easy (and without cost) for those who are already planning to apply N to a soybean field in 2015, but we hope that others want to do this as well.

        Having a crop on 10 million Illinois acres that doesn’t require N fertilizer is a great advantage under today’s pressures to have crop production remain “sustainable” and to decrease the amount of N going into the rivers. We simply cannot afford to start applying N to large acreages of soybean without knowing if it’s providing a response. We do know that, at least in some years, fertilizer N applied in July or early August won’t all be taken up by the crop, and that part of any N from fertilizer left in the soil after soybean harvest will end up in tiles lines. Can we afford that?

        I’d be glad to hear from anyone with questions about this, and from those who are interested in running a trial or two in 2015.

        Spring Cover Crop Field Day March 26th – Ewing Demonstration Center

        Join us on Thursday, March 26th, 2015 for the  Spring Cover Crop Field Day at the University of Illinois Extension Ewing Demonstration Center.  Registration will start at 8:30 a.m. and the program will begin at 9:00 a.m., rain or shine.  The Ewing Demonstration Center is located at 16132 N. Ewing Rd; Ewing, IL 62836, on the north edge of the village of Ewing, north of the Ewing Grade School on north Ewing Road.  Watch for signs.

        Cover crops have many benefits to the soil, environment, and overall crop production and management.  Topics covered during this field day program include:

        Challenges of Grazing Lush Spring Forage

        –          Travis Meteer, Extension Educator, U of I Extension

        Techniques for Planting into Cover Crop Residue

        –          Mike Plumer, Private Consultant

        Understanding the Soil Profile Beneath Your Feet

        –          Bryan Fitch, Resource Soil Scientist, NRCS

        Which One to Choose? Cover Crop Species Selection and Demonstration Trial Tour

        –          Nathan Johanning, Extension Educator, U of I Extension

        Some of the program highlights will be the demonstration trial planting of cover crops, including 17 different cover crops and combinations illustrating first hand the characteristics of the cover crops and what benefits they bring to your soil and crop production system.  Also, (weather and soil conditions permitting) we will have a soil pit dug, exposing the soil profile, where NRCS Resource Soil Scientist, Bryan Fitch will lead us through the characteristics of our southern Illinois soils to enhance understanding of the importance of a healthy soil.  Also Certified Crop Advisor CEU credits will be available (2.0 Soil & Water Management & 1.0 Crop Management) for the program.

        This field day will be free and open to anyone interested in learning more about cover crops.  A light lunch will be provided and this is a great way to talk to fellow growers to learn more from their challenges and successes incorporating cover crops into their cropping systems.  Please call the Franklin County Extension Office at 618-439-3178 for more information and to register by March 24th.  We hope to see you there!

        Brownstown Agronomy Research Center Cover Crop Field Day – Nov. 13

        Mult-species cover crops

        Mult-species cover crop trial - Brownstown Agronomy Research Center


        University of Illinois Extension and the Fayette County SWCD are hosting a Cover Crop Field Day on Thursday, November 13, 2014 from 9:00 – 11:00 a.m. The field day will be held at the U of I Brownstown Agronomy Research Center, 1588 IL 185, Brownstown, IL (Directions here).

        The field day will include tours of the current cover crop research trials being conducted at the Center. Extension educators and NRCS field staff will be on hand to discuss cover crop species selection, the effects of planting date and seeding method on cover crop establishment, factors influencing soil health, as will share their experience on the challenges and successes of cover crop establishment. 2.0 CCA-CEU credits in Soil & Water Management have been requested.

        For more information, contact:

        Robert Bellm,  U of I Extension

        Tony Pals, Fayette County SWCD
        618-283-1095, ext. 3

        Ewing Demonstration Center Fall Cover Crop Field Day – Nov. 6th

        Join us on Thursday, November 6th, 2014 for the the Ewing Demonstration Center Fall Cover Crop Field Day.  Registration and refreshments will start at 8:30 a.m. and the program will start at 9:00 a.m., rain or shine.  The Ewing Demonstration Center is located at 16132 N. Ewing Rd; Ewing IL 62836, on the north edge of the village of Ewing, north of the Ewing Grade School on north Ewing Road.  Watch for signs.

        Cover crops have many benefits to the soil, environment, and overall crop production and management.  Topics included in this field day program are:

        Establishment Challenges and Successes

        – Robert Bellm, Extension Educator, University of Illinois Extension

        Calibrating Success:  Drill and Planting Calibration

        – Marc Lamczyk, Program Coordinator, University of Illinois Extension

        Which One to Choose? Cover Crop Species Selection and Demonstration Trial Tour

        – Nathan Johanning, Extension Educator, University of Illinois Extension

        In addition, we also have a demonstration planting of cover crops established late this summer so you can view the growth and characteristics of the cover crops first hand and learn more what benefits they bring to your soil and crop production system.

        This field day will be free and open to anyone interested in learning more about cover crops.  Please call the Franklin County Extension Office at 618-439-3178 for more information and to register.  We hope to see you there!

        Volunteers Needed for Sampling Corn Grain

        In June with wheat harvest underway, I asked people to send in grain samples so that under an NREC-funded project we could measure P and K levels to try to sharpen up our nutrient removal numbers.

        We got a few wheat samples. We also, thanks to the Illinois Soybean Association, found a way to get a good number of soybean samples to measure P and K after they are tested for protein and oil.

        Our real need now is to get corn grain samples from the 2014 harvest. Thanks to some generous volunteers, we’ve been able to cover getting samples from most of southern Illinois and parts of the rest of the state. The biggest need we have now is for samples from Illinois north of I-80, and in central Illinois with the exception of the westernmost part of the state.

        We’re not trying to get uniform coverage across the state, but would like to find people who could gather 20 to 30 samples per county in the large corn-growing counties, with some samples from each county. Individual producers can send in samples from several different fields, but having volunteers to take samples within a county or area will be more efficient. Maybe a group of producers getting together for a meeting could each bring 3 or 4 samples.

        The process of collecting samples is as painless as we can make it:

        1. Each volunteer sends an email to giving the number of sample bags he or she would like and the shipping address to which they should be sent. The shipment of the bags will include a box (or boxes) with prepaid shipping labels so samples can be sent to us here at the University of Illinois.

        2. Each bag will have a blank label to record the field location. We prefer GPS coordinates, or ZIP code if GPS isn’t possible. The only other thing we’re asking for is yield level – just an estimate for the field. If the sample comes from a combine it can be the monitored yield level in the area of the field where the sample was collected.

        3. Each sample should be about 200 g (6 ounces) of grain, or about two handfuls.

        4. When all samples have been collected, send them in the box provided with the prepaid shipping label. Send them early in the week so they don’t sit over the weekend if there is wet grain.

        5. For those who want to see the numbers from their own samples, we’ll put a blank on the label for an email address – this will be optional.

        Please email me if you have any questions about this. And thanks for the help.

        Destructive diseases of soybean – sudden death syndrome and white mold – observed in the state

        Signs and symptoms of a few soybean diseases have begun to show up in the last few weeks in some areas of the state.  Two of these diseases, sudden death syndrome (SDS) and Sclerotinia stem rot (a.k.a. white mold) certainly are going to cause economic losses in some growers’ fields this year.

        Symptoms of SDS that currently are being observed are interveinal chlorosis and necrosis of the leaves (veins remain green while the tissues between the veins turn yellow and then brown).  These symptoms look exactly like the foliar symptoms caused by a different disease, brown stem rot.  Brown stem rot, however, will cause internal browning of the pith in soybean stems, while SDS does not affect soybean stems.  On SDS-affected plants, the leaves will fall off eventually, while the petioles will remain attached to the stems and branches.  In some cases, a bluish-white mass of spores of the SDS fungus (Fusarium virguliforme) may be observed on the roots.  Although the foliar symptoms of SDS are now being observed, infection by the SDS fungus occurred during the seedling stage, not long after planting.  The symptoms that are now being observed are the effect of toxins that the SDS pathogen produces that are phytotoxic.  Cool and wet weather after planting and the recent rainfall received in parts of the state were favorable for infection and disease development, and are the reasons why SDS incidence is high in some areas this year.  The primary method of managing SDS is to choose the most resistant soybean varieties available.  Some evidence has shown that high soybean cyst nematode (SCN) egg populations may also increase the likelihood of severe SDS; therefore, managing SCN populations through resistant varieties and crop rotation may also reduce the risk of SDS.  Unfortunately, there currently are no fungicide products registered that are effective in managing SDS, but an experimental fungicide seed treatment known as “ILeVO” that is currently making its way through the EPA registration process has shown efficacy against SDS in University of Illinois field trials.

        Symptoms of sudden death syndrome of soybean (Photo by C. Bradley).


        A bluish-white mass of spores of the SDS fungus (Fusarium virguliforme) on a soybean root (Photo by C. Bradley).


        White mold can be observed in fields located in the northern half of Illinois this year.  The appearance of this disease also is weather-related.  Areas in the northern half of the state, that were cooler and wetter than normal after soybean plants began to flower, are the areas that are affected the most severely.  Unfortunately, once white mold signs and symptoms are detected in the field, fungicide applications generally will be futile, as the damage has already been done.  Management of white mold was discussed in an earlier article of the Bulletin this year (  Growers with severe levels of white mold may encounter some discounts at the elevator this year for high levels of foreign matter.  Some sclerotia (dark survival structures produced by the white mold fungus – Sclerotinia sclerotiorum) that are formed on plants may similar in size to the seed, and will make their way to the hopper and eventually the elevator, where discounts may be received.


        Soybean plants dying prematurely because of white mold in a field in Champaign County (Photo by K. Ames).


        White mycelia of the white mold fungus (Sclerotinia sclerotiorum) on a soybean plant (Photo by C. Bradley).

        2014 Ewing Demonstration Center Fall Field Day

        2014 Ewing Demonstration Center Fall Field Day

        The University of Illinois Extension will host its annual Ewing Demonstration Center Fall Field Day on Thursday, September 11, 2014 at 9 a.m.  The Ewing Demonstration Center at is located at 16132 N. Ewing Rd; Ewing IL 62836, on the north edge of the village of Ewing, north of the Ewing Grade School on north Ewing Road.  Watch for signs.

        The ongoing research plots this year consist of a soybean cover crops trial, LibertyLink soybean variety trial, insecticide/fungicide trial on soybeans, corn population study, drought tolerant corn hybrid evaluation, and new this year a pumpkin variety trial.


        The topics to be discussed at Field Day include:

        Fusarium Head Blight (Scab) and Vomitoxin Management in Wheat

        • Carl Bradley, Extension Specialist, Plant Pathology, University of Illinois Extension

        Sky High Crop Scouting; Unmanned Aerial Drones

        • Dennis Bowman, Extension Educator, University of Illinois Extension

        Alternative Forages and Harvesting Methods

        • Teresa Steckler, Extension Educator, Commercial Ag, University of Illinois Extension

        Palmer Amaranth: Coming (Soon) to a Field Near You

        • Robert Bellm, Extension Educator, Commercial Ag, University of Illinois Extension

        Cover Crops and Weed Management

        • Nathan Johanning, Extension Educator, Small Farms Local Foods, University of Illinois Extension

        Refreshments will be provided by Franklin County Farm Bureau.

        The field day is free and open to anyone interested.  A light lunch will be provided and registration is recommended by September 8, 2014 for an accurate meal count.

        For additional information or to register, contact Marc Lamczyk at University of Illinois Extension Office in Franklin County at 618-439-3178 or


        Did We Miss the Boat on Corn Plant Population in 2014?

        One of the speakers at the UI Agronomy Day at Urbana this past week was quoted as saying that corn producers had not planted enough plants this year to take advantage of the good growing conditions. The assertion was that 45,000 plants would have been more appropriate than 32,000 plants. Most produces are planting more than 32,000 now on more productive fields. But few are pushing populations into the mid-40,000 range, at least on a lot of acres. Did we all miss the boat by planting “only” 35,000 or 36,000 seeds this year?

        Fortunately, we have a lot of data to help answer this question. Since 2011, we have been running trials at a dozen sites around Illinois in which we plant 6 to 8 hybrids at a range of populations, including planting rates of 34,000 and 42,000. Plant counts show that actual stands are very close to planted populations. Counting each hybrid at each site each year as a comparison, we have accumulated 277 comparisons of 34,000 and 42,000 plants over the past three years.

        Figure 1 shows all of these data, graphed to compare the yield change when going from 34,000 to 42,000 plants against the average yield at the two populations. On average the difference in yield between these two populations was only about a tenth of a bushel, and there was no indication that the response got larger as yield level increased; in fact, the line drawn through the points shows slightly lower yield differences as yield level increased.


        Figure 1. Corn yield difference between 34,000 to 42,000 plants per acre in 277 comparisons in Illinois trials, 2011-2013.

        At yield levels less than 150 bushels per acre, 42,000 plants yielded 9 bushels more than 34,000 plants, with a range of -62 to +48 bushels. At yields above 250 bushels per acre, 42,000 plants yielded a half bushel less than 34,000 plants, and the range was -24 to +24 bushels. This reinforces what many of us know – that low-yielding conditions tend to make yield less consistent, with more differences due to factors like hybrid stress tolerance water-holding capacity within fields.

        These data give no support to the idea that a corn crop planted at populations in the mid-30,000 range is incapable of taking full advantage of high-yielding conditions. The data also confirm that risks of having populations too high for the conditions increases when we don’t have conditions for high yields.

        Because we don’t know what conditions will be at the beginning of the season – the 2012 season started off great and would have been a “good” season to raise populations at planting – it makes no sense to push populations above 40,000 in hopes that we’ll get the weather to make this pay off. In fact, the response of yield to population tends to be fairly flat over the range of the lower to the upper 30,000s, regardless of yield level or conditions.

        A Good Crop Takes Shape

        The “walls” of dark green corn as the crop begins its push to fill grain and make yield is always an inspiring sight, and the 2014 crop is the best I’ve seen at stage of development. It’s been almost this good in June several times, but not at the end of July. The crop condition rating has been stuck at about 80% good to excellent, and this remarkable uniformity is apparent in travels around northern and western Illinois in recent weeks.

        The same is true for the soybean crop, though the condition rating isn’t quite as high, and there are areas where the crop doesn’t look great.

        Without many serious problems to look at, this is a good time to consider whether this crop will turn out to be as good as it looks, and what threats might linger as we move into the 6 weeks over which yield will be made:

        • Nitrogen: Despite a lot of rainfall in May and June (into early July in some places), the deep green color of the corn crop in most fields tells us that the crop is well-provided with nitrogen. While water moving through the soil has undoubtedly moved some of the nitrate deeper, the fact that adequate N has clearly been taken up has to be a consequence of having a healthy root system that is active deep enough to take up what N is there. Plots without N in rate trials are very deficient, probably due to both downward movement of N and root systems that are feeble due to poor N nutrition and growth of the crop. But the crop is green all the way to the lower leaves in fields with normal N rates, and so we don’t anticipate that the 2014 crop will require more than normal amounts of N. Recent N Watch samples show that soil nitrate values have dropped considerably over the past month, but that’s as is should be – we apply fertilizer N for the crop, not to accumulate in the soil. Uptake of N by the crop has slowed considerably as the crop moves past pollination, and we see little reason to worry about having enough N in the soil now. Mineralization of organic matter is providing N that will serve as backup, but the crop has taken up 80 to 85% of the N it will take up by the end of the season. Stress from hot, dry weather is about the only threat to the N status of corn plants beyond this point in the season, and with another stretch of cool weather coming now, chances of having this happen in time to hurt yields are diminishing
        • Water: I’ve likened the corn crop this year to last year’s crop about 10 days later than this; the 2014 crop was planted earlier and had normal temperatures through June, plus enough water to make good growth and to reach at least normal height. Excess water has certainly done some damage in some fields, and in cases the roots in low areas that were flooded for a week or more, they (and crop prospects in those areas) are damaged to the point where they won’t recover much. In 2013, there was in some areas little rainfall after August 1 all the way to crop maturity; the soils had to have provided the 8 inches or more of water required to fill grain after the milk stage of kernel development. This year, soil water is in better supply than it was at the beginning of August last year, and the cool conditions over the coming weeks will help stretch the water supply even further. The crop might benefit from some additional rainfall within the next month, but highs of only 80 or so plus lots of sunshine are excellent conditions for corn grainfilling, and with roots that have done a good job up to now, we don’t see much danger of having the crop run out of water.
        • Kernel number: We cannot produce good corn yields without high kernel numbers, even though in very good years kernels often get larger than they would otherwise. A starting point is maybe 15 million kernels per acre, which at 75,000 kernels per bushel (such kernels are a little above average, but not huge) would produce 200 bushels per acre. At 35,000 ears per acre, it takes only about 430 kernels per ear to make 15 million per acre. That’s not a large ear – at 16 rows of kernels, it’s only 27 kernels long. At 14 rows of kernels, it takes 4 more kernels per row to get to the same count. Someone recently mentioned the disappointment of finding ears with only 14 or 16 rows of kernels; it seems that people like to see 18 or 20 rows. The number of rows of kernels is influenced much more by hybrid genetics than by conditions in the field, and fewer rows are typically compensated by having more kernels per row, so have similar numbers of kernels per ear. This year, we may see kernel number approaching or exceeding 20 million per acre, which at 35,000 ears per acre would be 570 kernels per ear. At 14 rows that’s about 40 kernels per row, still easily within range of possibility. Kernel abortion should be less than normal, so kernels we can count by the time silks are brown will be mostly retained into grainfill, with any effect of stress late in the season seen as a reduction in kernel size.
        • Ear number: Stands are mostly good and ear numbers should be as well. There have been some reports of more than one ear per plant, including what Dr. Bob Nielsen calls “multiple ears on the same shank” or MESS (see The second (or third) ear on the same shank usually doesn’t produce kernels. In contrast, having ears at two separate nodes, with both producing grain, is the way that some hybrids today cope with having more than usual amounts of resources (sugar from photosynthesis) available before and at the time of pollination. Many older hybrids respond to this by increasing ear size, up to 800 or more kernels. Many hybrids today form a second ear instead. Making two smaller ears instead of one big one carries a little high “construction” cost, but with a shorter path from the stalk to the tip kernels, two smaller ears may have some advantage in getting the kernels filled if filling conditions are very good. To estimate yield potential of there are a lot of second ears, kernels per plant should be counted, with kernel size perhaps adjusted downward slightly if there are more than 750 or so kernels per plant. Should populations have been higher if there are 700 or 750 kernels per plant? Perhaps, but that many kernels may end up smaller, and not yield much less than more plants with fewer kernels each.
        • Canopy: If you can see down rows of corn, a good canopy will have healthy leaves interlaced to intercept nearly all of the sunlight, and you’ll find little light hitting the soil surface when the sun is high. If the crop gets enough water to maintain this canopy up to close to the end of grainfill, kernels will approach their maximum size (which has been determined by now in most fields, and with good conditions at pollination is likely to be large) and yields will be high. The corn crop needs about 1,300 growing degree days from pollination to maturity (black layer). At normal temperatures from mid-July into September, we get about 24 GDD per day, so getting 1,300 GDDs takes about 55 days. With temperatures on the cool side, at 55 nighttime and 80 daytime, that’s 17.5 GDD per day and it takes some 70 days to get to 1,300 GDD. With pollination nearly completed now, the crop should reach maturity by late September even if it stays this cool, but some warmer temperatures would be welcome, as long as it doesn’t go to the mid-90s and stay there. Cool nights are good, but 60 or 62 instead of 55 degrees would probably help more than hurt.
        • Standability: Having lots of kernels and conditions for potentially high yields often brings concerns about whether high yields might mean stalk quality problems later in the season. It is certainly the case that in the competition for sugars between developing kernels and stalk tissue, stalks usually lose. But when conditions are very good after pollination, as they were in 2013, plants are able to allocate enough sugars to help stalks deposit lignin, which is the woody material that gives stalks strength and helps keeps them standing even after the stalk tissue dies. So while there’s always some cause for concern about the possibility of high winds and downed corn, I see no reason for much alarm because we expect high yields.
        • So how high will yields be? This is the point at which we should humbly admit that we don’t know everything about the corn crop, that every year is different, and that we don’t want to guess. Facts in favor of a new record corn yield in Illinois in 2014 include a crop that’s in great shape now, above-average soil water stored in most areas, and lack of any evidence that a blocking high will set up to bring hot, dry conditions in time to shorten the filling period by much. But such hopes aren’t always realized, and it remains safer not to speculate on final yields.

        I’ll continue the story on soybeans later, but will only note here that the dry weather we’ve had in recent weeks has been favorable for the early-planted crop, which had been starting to show signs of making the large leaves and tall plants that we have in the past found to produce mediocre yields. But the late-planted crop seems stunted in some areas, and lack of moisture could be limiting growth enough to affect canopy cover and yield potential. These problems are not beyond fixing in soybean fields, but at this point in the season what may be ideal conditions for the corn crop may be less than ideal for soybeans.