Tracking Soil Nitrogen – Does Corn Have Enough N?

Rainfall in April and May has been about average through most of Illinois, at least until the downpours the last days of May. This has allowed timely planting and a good start to the crop in most areas, and has allowed nitrogen management to be carried out more or less as planned by most producers. Warm temperatures during some weeks of May are moving crop development along, and much of the N planned for application after crop emergence has already been applied.

Much of the rainfall has come with low or moderate intensity; there have been few multiple-inch downpours leading to standing water and fears of crop damage and of loss of nitrogen, though rain on May 30 has been heavy in places. But reapplying N late or using higher rates due to expectations of N loss happen every year, and while that might be less common this year, it remains a consideration.

To find out if more N is justified, we initiated a new study this year, funded by NREC, to “track” N applied at different times and forms to see how much N remains in the soil and available to the crop through the vegetative growth period. At four research center sites in central and northern Illinois, we applied 200 lb of N in four different ways: 1) as NH3 applied in November 2014; 2) as 100 lb NH3 last fall + 50 lb UAN at planting + 50 lb UAN as V5-V6 sidedress; 3) as NH3 applied in early-mid April; and 4) as 50 lb UAN at planting + 150 lb UAN at V5-V6 sidedress. The 200-lb rate is higher than the N rate calculator rate, which is about 160 lb N for corn following soybean; our objective is to track N over time. Beginning after the fall application and about every 10 days this spring, we have been sampling soil to 2 feet deep, with samples analyzed for both nitrate and ammonium.

Figure 1 shows how much soil N (nitrate plus ammonium) we’ve found at the Urbana site in samples taken so far. Sampling like this always finds a fair amount of variability – we don’t know exactly where the N ended up in the soil, and soil probes don’t always get a representative sample. But we did find more N in plots where we had applied N, and we are able to see changes in soil N as the soils have warmed up and mineralization has kicked in. About as much fall-applied NH3 remains available as spring-applied NH3; both show at least 250 lb of available N in the top two feet on May 22. We think this confirms that N losses have been small since last fall.

Figure 1. Soil N at different sampling times in an N-tracking trial at Urbana in 2015. Fall NH3 was applied before the November 14 sampling, early spring NH3 before the April 7 sampling, and planting-time applications (as UAN) were made before the April 24 sampling. Pl is planting time and SD is sidedress, which was done after the May 22 sampling. The 2014 crop was soybean, and corn was planted on April 23.

Figure 1. Soil N at different sampling times in an N-tracking trial at Urbana in 2015. Fall NH3 was applied before the November 14 sampling, early spring NH3 before the April 7 sampling, and planting-time applications (as UAN) were made before the April 24 sampling. Pl is planting time and SD is sidedress, which was done after the May 22 sampling. The 2014 crop was soybean, and corn was planted on April 23.

One surprise at this site has been the relatively large amount of N found in the soil where no fertilizer N was applied. In soils with a good amount of organic matter we never expect to find zero N, but we would not have expected to find the 130 to 180 lb of N that we found in the last three (May) samples. Still, getting yields of 125 to 150 bushels per acre in corn following soybean without N fertilizer is not unusual, and so finding this amount of N may not be abnormal.
The findings at DeKalb and Monmouth are similar to those at Urbana, though the soil N levels are a little lower at the other sites, in part because they were last sampled a little earlier than at Urbana. Soil N without N fertilizer has yet reached only about 100 lb per acre at those two sites. At the Perry site, with soils lower in organic matter, levels of soil N we have been finding are considerably less than at the other three sites; at the May 22 sampling at Perry, we found only about 150 lb of soil N in both the fall- and spring-applied NH3.

The majority of the soil N is now in the nitrate form, regardless of what form was applied (Figure 2.) This is more or less as we expected for fall-applied NH3 and for spring-applied UAN, but by about six weeks after early spring NH3 application (done on April 6) we might have expected a little more of the N to still be in the ammonium form. As expected, most of the N found in plots without N fertilizer was in the nitrate form regardless of when sampling was done. Mineralization releases ammonium, but under the soil temperatures that increase mineralization rates, the ammonium converts to nitrate quickly.

Percentage of soil N present as nitrate following different N treatments and at different sampling times at Urbana. The rest of the N was present as ammonium.

Percentage of soil N present as nitrate following different N treatments and at different sampling times at Urbana. The rest of the N was present as ammonium.

The takeaway message from what we’ve found so far in this project is that we see no reason to adjust upward the total amount of N applied due to concerns about N loss. The fertilizer N that was applied is mostly present as plant uptakes begins, and we can add to that the N coming from soil organic matter. It’s also encouraging that the amount we’re finding has continued to increase as we move into the N uptake period. Last year we found that the crop took up a total of less than 1 lb of N per bushel of yield, so we don’t see a shortage for the crop coming anytime soon.

As part of this project we are also working with Dan Schaefer (IFCA) to sample several on-farm sites with similar treatments, and we’re sampling following spring N applications at two southern Illinois sites. We’ll keep you posted on what we find in the coming weeks.

2015 Field Day Events in Illinois

Fields days organized by Crop Sciences and Extension at the University of Illinois and by other institutions will focus on crops and pests, with speakers talking about current crop issues along with information from previous research. Each event will offer CEUs for CCAs.

Following is the schedule of crop-related 2015 field days organized by University of Illinois Crop Sciences and by several other institutions.

Event Date – start time Food Contact
Urbana – Weeds June 24 – 8:00 AM lunch Doug Maxwell (217) 265-0344
Macomb – WIUa June 25 – 12:00 N lunch Mark Bernards (309) 313-5917
DeKalb July 9 – 9:00 AM lunch Russ Higgins (815) 274-1343
Belleville – SIUb July 9 – 9:00 AM lunch Ron Krausz (618) 566-4761
Orr Center, Perry July 22 – 9:00 AM lunch Mike Vose (271) 236-4911
Monmouth July 28 – 8:00 AM snack Angie Peltier (309) 734-5161
Brownstown August 5 – 8:00 AM lunch Robert Bellm (618) 427-3349
Dixon Springs August 6 – 9:00 AM lunch John Pike (618) 695-2790
Urbana August 20 – 7:00 AM lunch Bob Dunker (217) 244-5444
Urbana August 31 – 8:00 AM International Agronomy Day:
Ewingc Sept. 10 – 9:00 AM lunch Mark Lamczyk (618) 439-3178
aWestern Illinois University conducts this field day at its Macomb research farm.
bBelleville is a research center operated by Southern Illinois University–Carbondale.
cEwing Field is operated by University of Illinois Extension in southern Illinois.


Stripe rust and Fusarium head blight (scab) concerns in Illinois

Stripe rust of wheat has been observed in different parts of Illinois within the last week. Although some varieties have very good resistance to stripe rust, there are still several varieties that are susceptible. Stripe rust is able to flourish under the cooler temperatures we’ve had over the last few days. With rain in the forecast in parts of the state over the next few days, favorable conditions for this disease likely will continue.

Although some wheat fields in the state are already past the critical period for applying a fungicide for protection against Fusarium head blight (a.k.a. scab) (beginning flowering up to 6 days after beginning flowering), some fields in the state are just beginning to flower or will within the next week. For the fields that are just beginning to flower or will within the next week, an application of Prosaro or Caramba fungicide should be considered for protection against Fusarium head blight and stripe rust. Multi-state university research has indicated that Prosaro and Caramba are the best products available for managing Fusarium head blight and the associated mycotoxin, deoxynivalenol (DON; a.k.a. vomitoxin). Both of these fungicide products also have efficacy against the stripe rust pathogen.

Light-orange colored stripe rust pustules on wheat leaves (Photo by C. Bradley).

Light-orange colored stripe rust pustules on wheat leaves (Photo by C. Bradley).


Wheat disease outlook

As the weather begins to warm up, wheat is beginning to grow at a faster pace.  Symptoms of some diseases also are beginning to appear or will likely be appearing soon.  Below are some diseases to look for right now.

Stagonospora and Septoria leaf blotch: Although caused by two different pathogens, symptoms of these two foliar diseases look very similar and both can be managed with an appropriate foliar fungicide application.  Most results from University of Illinois wheat foliar fungicide trials conducted since 2008 have shown that an application of an effective fungicide for control of Fusarium head blight (scab) when wheat is beginning to flower also provides good protection against common foliar fungal diseases on the flag leaf.  However, if a variety is very susceptible and if conditions are favorable (frequent rainfall / damp conditions), then an application of a fungicide when the flag leaf emerges may be needed.  On a side-note, the 2015 multi-state university foliar fungicide efficacy table for wheat diseases can be found here: NCERA 184 Wheat fungicide table 2015_V3.

Septoria leaf blotch symptoms on a wheat leaf. (Photo by C. Bradley)

Virus diseases: Surveys of viruses affecting wheat in Illinois conducted in recent years indicate that Barley yellow dwarf virus (BYDV) is the most commonly detected virus affecting wheat in the state.  However, other viruses, such as Wheat spindle streak mosaic virus (WSSMV), Soilborne wheat mosaic virus (SBWMV), Wheat streak mosaic virus (WSMV), and a few others also have been detected.  Virus symptoms (yellowing, purpling, yellow streaks, etc.) can be confused with other disorders, and it can be extremely difficult identifying a virus disease by symptoms alone.  Therefore, specific laboratory tests must be conducted to determine if a virus is responsible for these symptoms.  The University of Illinois Plant Clinic ( does not currently test for viruses in wheat, but can help make a determination if virus testing is needed.  Plant virus testing can be done at the Purdue University Plant & Pest Diagnostic Laboratory ( and at a private lab known as Agdia, which is located in Elkhart, IN (  Unfortunately, no in-season control options are available for managing virus diseases.

Symptoms caused by Barley yellow dwarf virus on wheat. (Photo by C. Bradley)

Symptoms caused by Soilborne wheat mosaic virus on wheat. (Photo by C. Bradley)

Stripe rust: To my knowledge, stripe rust has not yet been detected in Illinois during the 2015 season.  However, there have been reports of stripe rust from states to the south of Illinois, such as Arkansas and Tennessee.  Since rust spores have the capability of moving many miles, stripe rust could be on its way to southern Illinois.  If stripe rust is observed on plants, a foliar fungicide may be needed to protect the flag leaf, depending on the susceptibility of the variety.  Applications at early flowering for control of Fusarium head blight also may be effective in managing stripe rust; however, an earlier application of a fungicide may be needed if stripe rust is found prior to heading and if disease is developing rapidly.

Early symptoms of stripe rust on a wheat leaf. (Photo by C. Bradley)

Orange-colored pustules of the stripe rust fungus on a wheat leaf. (Photo by C. Bradley)

Fusarium head blight (scab): Although it cannot be observed yet, Fusarium head blight is the most important wheat disease in Illinois, and thinking about how to manage this disease cannot occur too early.  In years in which weather is favorable for infection (frequent rains, moderate temperatures, and cloudy weather – such as 2014 for southern IL producers), this disease can wreak havoc.  This is especially true because the fungus that causes this disease also produces toxins, such as deoxynivalenol (DON; also known as “vomitoxin) that will contaminate grain and will result into major dockage when grain is delivered to the elevator.  Infection of the scab fungus occurs when wheat heads begin to flower.  The beginning flowering stage also is the best timing for applying an effective fungicide to managing Fusarium head blight and DON.  Results of university fungicide trials across multiple states have shown that Prosaro (Bayer CropScience) and Caramba (BASF) are the best products currently available for reducing Fusarium head blight and DON in grain.  One thing to keep in mind with these fungicides is that 100% control cannot be achieved, and susceptible varieties cannot be “fixed” by applying a fungicide when conditions are very favorable for Fusarium head blight.  University research has shown that Fusarium head blight and DON can be reduced by approximately 40%-60% with Prosaro or Caramba (relative to a non-treated check); therefore, the bottom line is that fungicides will reduce disease and DON levels in grain, but don’t expect a complete reduction with fungicides alone.  The forecasted risk of Fusarium head blight can be observed by going to the Fusarium head blight Prediction Center website (

Fusarium head blight (scab) affecting a wheat field. (Photo by C. Bradley)

Planting into Cool Soils – Yes or No?

While research shows that the last 10 days of April is on average the best time to plant corn in Illinois, expectations of below-normal temperatures in most of Illinois during the last week of April has some wondering if it makes sense to plant now or to wait until temperatures warm up.

Averaged over the past 22 years, Illinois corn producers have planted 16% of the crop by April 20. NASS reported that 15% of the crop was planted by April 19 this year, so planting progress to date is right at the average. There will be some progress to report this week, though rainfall coupled with cooler temperatures will limit the rate at which fields get ready to plant in some areas. Still, we may be on track to maintain planting progress at the average rate, which would mean having close to 40% planted by April 30.

Research tells us that planting before May 1 almost always yields more than planting later, with yield loss accelerating with delays past early May. Planting date and yields over years for the whole state often give a different picture, however.  Over the past 22 years, in fact, there has been no correlation between the date by which 50% of the corn crop was planted and statewide yield, measured as departure from trendline yield in order to correct for the upward yield trend over time.

In 2014, 36% of the Illinois corn crop was planted by April 30, and the average yield was 200 bushels per acre. In contrast, 81% of the crop was planted by April 30 in 2012, but the average yield was only 105 bushels per acre. Two of the latest-planted crops in recent years – 2009 and 2013, with hardly any corn was planted by April 30 – produced yields more than 10 bushels above trendline yields. So it is clear that what happens with weather during the season can override when the crop was planted, at least over a large area.

But for each individual field we still need to try to plant as early as conditions allow. Even if planting a week or two later would have little effect on yield in that field that year, we need to “start so we can finish” – getting all fields planted by early May is a goal as we try to maximize yield potential. But might this year be an exception, with potential for harm from planting into cool soils in the last week of April, with the weather forecast indicating that temperatures may stay low for the next week?

As a principle, waiting until soil is dry enough to allow planting into good seedbed and rooting (less-compacted) conditions is more important when soils are cool than when they are warm. We never want to work soils wet and plant under wet soil conditions if we can help it, but we certainly do not want to do that in April, especially when soil temperatures are less than normal.

So our first question should be whether or not the soil is dry enough; if the answer is no, then we wait. Cool soils dry slowly, and wet soils warm slowly, so waiting might take an extra measure of patience, especially if a neighbor brings out the planter. There is some comfort in the fact that germination and emergence are slow in cool soils, so planting a few days earlier when it’s cool makes very little difference in how far along the crop will be on a given date later in the season.

According to the Illinois State Water Survey, minimum temperatures 2 inches beneath bare soil on April 21 averaged about 40 degrees in the northern half of Illinois and in the upper 40s in southern Illinois. That’s a drop of more than 10 degrees over four days. And the weather forecast indicates that soils may not warm up much by the end of April. If we go by the old standard recommendation that corn should be planted only after the minimum soil temperature 2 inches deep exceeds 50 degrees, we would have planted for perhaps half the days in April through April 19, but none since then. Maximum temperatures 2 inches deep reached the 80s on April 17, but only averaged in the low 60s on April 21.

It takes soil temperatures of 50 or above to get the germination process underway, but does this mean that we should avoid planting corn into soils where temperature at seeding depth averages less than 50? Based on a lot of planting date work, we would say that the danger from doing this in minimal. It takes about 115 or so growing degree days (GDD, based on air temperature) after planting to get corn plants to emerge, and emergence has usually been good even when it has taken 3 weeks for this number of GDD to accumulate. Planting date has had little or no effect on emergence in most of these trials.

Normal GDD accumulation in the month of April ranges from about 180 in northern Illinois to 220 in central Illinois to 300 in southern Illinois. So far in April 2015, we have had about 200 GDD accumulate at Urbana. With the slowdown this week, the total will end up somewhere around the average for this month. We made our first planting here in the planting date trial on April 1, and it emerged more or less on schedule, around April 16. We can expect corn planted on April 22 or 23 to take at least this long to emerge, and longer if temperatures don’t rebound next week.

The chances of getting good emergence when planting into cool soils are higher if here is little or no rain between planting and emergence. Cool soils bring slow germination and emergence, but they may lower the chance of emergence problems due to soil crusting or to saturated soil. Crusting problems usually develop after intense rainfall followed by warm, dry conditions that help “bake” the crust. Warm soils mean more rapid growth of seedlings, which can mean running out of oxygen sooner if soils become saturated. So while we would prefer warmer and relatively dry soils, next best is having cool and dry soils. Most stand problems occur when soils are warmer, simply because that’s when the plants are trying to grow faster. Still, warm soils help bring the crop up, and we hope that they start to warm soon.

Heavy rainfall is not predicted for this coming week or so, which is a positive. Taking the longer view, temperatures in May will inevitably start to rise at some point in time, and this will speed up emergence. Taking all the factors together, I would suggest that planting proceed as long as soil conditions are good, even if the germination process will be slow due to cool soils in the near term.

One of the concerns being mentioned is “imbibitional chilling injury” that has been reported when seeds and seedling take up water that is colder than 40 degrees. This can stiffen plant cell membranes and lead to damage, in some cases distorting growth and reducing emergence. This has usually been linked with melting snow or very cold rainfall after planting. It’s something to keep in mind, but it has been rare in Illinois (we think there was some in corn planted around April 20-25 in western Illinois in 2011) and it should probably not keep us from planting in the last week of April. Higher, drier fields are less likely to suffer from this, and should be planted first.

Spring Nitrogen Management – Form and Timing

Most corn producers have planned their spring N program for 2015, and many have already started to implement their program. Such plans might include fall ammonia application, early spring application of ammonia or another form of N, or plans to apply all of the N at or after planting. In recent years there has been a trend towards more applications per crop, and it’s not unusual today to have N applied three or four times on the same field.

In 2014 we initiated a large study with funding (from the Illinois fertilizer checkoff program) administered by the Nutrient Research and Education Council (NREC) board. One of our goals is to compare yields from different N programs. These included fall versus spring N and early spring versus split N applications in on-farm trials, and comparison of 15 different ways to apply the same rate of N in the spring in small-plot trials at several of UI research centers.

June rainfall at the three sites where we ran these trials in 2014 ranged from 8 to 10 inches, or more than twice normal amounts. This might have meant above-normal N loss potential, though we did not have water standing on these plots. We chose to use 150 lb of N as the rate for comparison; this compares to the MRTN (N rate calculator) rate of about 160 lb for corn following soybeans in central Illinois and of about 140 lb of N in northern Illinois. Using a “medium” N rate was intended to help bring out differences in N availability to the crop.

Yields at the different sites were similar at this N rate, ranging from about 200 to 220 at Monmouth and DeKalb, and from about 215 to 240 at Urbana (Table 1). Included in these trials was a full set of N rates, ranging from 0 to 250 lb per acre using UAN injected at planting time. The maximum yield at Urbana was 238 bushels per acre, reached at 230 lb N; at Monmouth the maximum yield was 235 bushels per acre reached at 224 lb of N; and at DeKalb the yield reached a maximum of 223 bushels at 225 lb of N. The range of yields at the 150-lb N rate applied using different forms and timings included the maximum yield (from higher N rates) in the trials at Urbana and DeKalb, but not at Monmouth.

While there were considerable differences among sites in how treatments ranked in terms of yield, most of the N forms and application times we compared produced similar yields when averaged across sites (Table 1). Over the three sites, the highest-yielding treatment (urea plus Agrotain broadcast at planting) yielded statistically more than the five treatments that yielded 215 bushels per acre or less, while the second-best treatment (all of the N as UAN sidedressed at V5) yielded significantly more than only the two lowest-yielding treatments (ESN and UAN + Agrotain, both broadcast at planting).

None of the other treatments differed significantly from one another, in large part because they changed rank so much from one site to another. When this happens, it lowers the predictive ability of experiments like this, since we have no way to predict how a treatment that did well at one site but not another will perform at either site (or across sites) in 2015 or 2016, or in your field this year or in future years. This is why we do trials at different sites over several years.

The 2014 results do raise the possibility that few if any of these N form and timing treatments may, in the end, stand out as being consistently better or worse than another. This isn’t alarming, but it does provide a hint that the list of “acceptable” ways to apply N might turn out to be a little longer than we might have thought. While we need to be cautious about any predictions, this also hints that some of the treatments that we’ve considered should produce higher N use efficiency – such as sidedress or split N applications – might not always do so consistently.

The highest-yielding treatment – urea + Agrotain all broadcast at planting – has not been a common method of applying N in Illinois, and may not even be considered by some to be a sound method. That we saw it do well in 2014 in no way means that it’s the “best new” way to apply N. But with Agrotain as protection against loss of N from urea due to urease activity, with urea sometimes competitively priced as a source of N, and with the speed and ease of application, this practice could gain some traction if it continues to do well compared to other treatments. It probably makes sense to wait until we see more results before committing to it, although running some strips to compare it against another method of N application might be worthwhile.

It’s dangerous to speculate about why a treatment might have done well at one site but not another based on weather differences between the two sites. In part that’s because the weather among sites was reasonably consistent in 2014 – rainfall was normal or below normal in May and above normal in June at all three sites, July was cooler than normal, and there was little stress throughout the season. It’s also the case that the weather in 2015 will probably be different than in 2014, with some of our more imaginative speculation overturned as a result. Delaying all of the N to sidedress UAN or splitting 100 lb at planting with 50 lb at sidedress did much better at DeKalb and Monmouth than at Urbana, perhaps reflecting more loss from early-applied N at those two sites. On the other hand, dribble-applying UAN at planting worked well at DeKalb but not at Monmouth. It’s not likely that we would have been able to find such differences in either the plants or the soils back at the time of application.

The 2015 trials will include fall-applied NH3, and a fall-spring split. We also added a treatment in which we’ll apply some of the N as late as tasseling time. This is a practice that some seem convinced is on its way to becoming common, given recent observations that newer hybrids take up a greater percentage of their N after pollination than older hybrids did. It is not at all clear why, even if plants take up 40 percent of their N after pollination, soil that was fertilized with N early in the season would be unable to supply that amount. In fact, N mineralization rates in mid-season run 3-4 lb of N per acre per day in better soils, and this would be enough to provide at least 40% of total crop N requirement (of roughly 1 lb per bushel) over the six weeks following pollination, whether or not any fertilizer N were still present in the soil. We’ll see what the data tell us.

Most of us can take comfort from the fact that just about any method we choose for putting N on the corn crop is likely to work reasonably well, though no method is entirely safe from unusual weather or crop conditions. We only need to look back to 2012 to find a year when no method of applying N worked very well; when water (too much or too little) becomes the main limitation for a crop, things like N management may make little difference.

A sound N management program should, though, take costs into account – not just the costs of trips across the fields and of the fertilizer material, but also the indirect costs that include such things as the chance for yield loss or of more expensive forms or application methods we might need to use if we can’t get N on when we expected to. Most changes we are inclined to make in how we manage N today involve increasing the complexity, and this often comes at a cost in time, expense, or uncertainty. Such costs have to be covered by consistent improvement in yields.

Table 1. Yield ranks of N form and timing treatments at three Illinois sites in 2014. The N rate was 150 lb per acre for all treatments. Unless otherwise indicated, UAN was injected 2-3 inches deep between rows, and urea, SuperU, and ESN were broadcast-applied. PT = at planting time; AT = Agrotain®; dribble = surface placement between rows. There was no incorporation by tillage.

Nitrogen Management – Avoiding Ammonia Injury

A lot of anhydrous ammonia is going on this spring, and in many fields the hope is to plant as soon as practicable after NH3 application. This brings up the question about potential for NH3 damage to seeds and seedlings.

Seed and seedling damage from spring-applied NH3 is relatively rare in Illinois, but it can be quite damaging, and we want to minimize the chances of it happening. Such damage is rare is because NH3 converts readily in soil to the ammonium form (NH4+) which is held on soil exchange sites and is not damaging to plant tissue. If soils are moist at the time of application and there is normal rainfall (or at least an inch or so) from NH3 application through the time of crop emergence and establishment, chances of damage are close to zero.

A small amount of NH3 remains as free ammonia instead of converting to ammonium right away, due mostly to the large increase of pH that accompanies conversion of ammonia to ammonium. If placement is shallow or if soils dry out, some ammonia can end up in the seeding or rooting zone. If you can smell ammonia at the soil surface near the row at or after planting and soils are dry, there may be enough to cause damage. Free ammonia is very toxic to young plant tissue, and if seeds are planted into, or roots grow into, a soil zone where there is ammonia, damage can result. The most common damage is death of young roots, and this can affect yield if root systems don’t fully recover.

The best way to avoid the potential for damage is to physically separate the NH3 and the seed by placing NH3 between rows or row locations. This is possible using GPS (probably RTK) and autosteer, but it means that NH3 needs to be applied parallel (not at an angle) to the rows, and application and planting need to be precise in order to avoid placing any rows right over the ammonia band. If this can be done accurately, planting can take place right after, during, or before NH3 application.

Physically separating NH3 from the seedling zone by placing NH3 deep can help, but does not eliminate the possibility of damage. Deep placement (8 to 10 inches deep) takes more power and it can be difficult to maintain uniformity of depth across wide bars. Deep placement in the spring also means placement into wetter soil. With its very high solubility, NH3 moves less distance away from the point of release in wet soils than in drier soils. This increases the concentration of ammonia in the soil, and increases the amount that might move up if soils dry to that depth. The “path” left by a knife running in wet soil is more open for upward movement of NH3, and this can increase potential for plant damage.

If it’s not possible to apply NH3 between (the eventual) rows, then separating application from planting by time can reduce damage potential. The idea is to apply NH3 early enough so that enough rainfall will occur to keep NH3 out of the seedling zone. This means relying on weather probabilities, but not certainties; there have even been some instances of plant damage from fall-applied NH3. But the chances of such damage are low, and if this is the only option, then the longer you can wait between application and planting the better. The old rule of thumb – to wait 1 to 2 weeks between application and planting – is better than waiting 1 to 2 days, but not as good as waiting a month. So as long as we understand that waiting a week or two decreases but does not eliminate the odds of injury, it’s a guideline we can live with.

Online Survey on Soybean Farming Practices

Soybean farmers who take a ten-minute online survey will help University of Illinois crop scientists and Extension educators to better understand how decisions are made in their farms regarding soybean management and inputs and to tailor programs and projects to improve yields and profitability.

Villamil requests that soybean farmers take the survey by April 10.

The survey is a collaborative effort between the Department of Crop Sciences in the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois, U of I Extension, and the Illinois Soybean Association. The Farm Journal-AgWeb Research will be distributing an invitation to participate in the survey by email.

Questions about the survey can be sent to María Villamil at or Anne Silvis at

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