Brownstown Agronomy Research Center Field Day – August 6

The 2014 Brownstown Agronomy Research Center Field Day, presented by the University Of Illinois Department Of Crop Sciences, will be held on Wednesday, August 6. Extension researchers and specialists will address issues pertinent to the current growing season. The tour will start at 8 a.m. and will last about two and a half hours. It will be followed by lunch provided by U of I Extension.

Shaded tour wagons will take participants to each stop. These topics will be addressed:

  • N Fertilizer for Soybean:  Where’s the Yield? – Jake Vossenkemper, U of I
  • Tillage is Recreational, Fertilizer is Essential – Dr. Rachel Cook, SIU
  • Field Crop Diseases & Fungicide Treatments – Dr. Carl Bradley, U of I
  • Corn Nematodes:  the Hidden Menace in Your Fields – Dr. Angie Peltier, U of I
  • Factors Contributing to a Healthy Soil – Troy Fehrenbacher, NRCS

The 208-acre Brownstown Agronomy Research Center has been conducting crop research on the claypan soils of southern Illinois since 1937. More than 30 research and demonstration projects are conducted at the Center every year. Visitors are always welcome.

The research center is located south of Brownstown on IL Route 185, approximately 4 miles east of the IL Route 40 / 185 junction.

For more information, contact Robert Bellm (618-427-3349); rcbellm@illinois.edu
Visit us on the web at http://web.extension.illinois.edu/barc/


Assessing the risk of white mold (Sclerotinia stem rot) of soybean in 2014

White mold of soybean (a.k.a. Sclerotinia stem rot), caused by the fungus Sclerotinia sclerotiorum, is a disease that can occur in the northern half of the state in cool, wet years.  The most recent, widespread white mold epidemic in Illinois occurred during the 2009 season, where several fields in the northern half of the state were affected.  In some of the northern-most areas of Illinois, white mold can be considered a more consistent problem.

The white mold fungus overwinters in the soil as, small, black, and dense structures known as sclerotia.  These sclerotia germinate and form mushroom-like structures known as apothecia when soil remains moist for several consecutive days and soil temperatures are at 60 degrees F or below.  These apothecia generally will not form until the soil is shaded from sunlight due to soybean canopy closure.  Spores of the white mold fungus are shot out of the apothecia and land on senescing flower petals, where infections first occur on the soybean plants.  The white mold fungus becomes inactive when temperatures within the soybean canopy are above approximately 82 degrees, so infection and disease development may cease or slow down during periods of hot (above 82 degrees) and dry weather.

Apothecia of the white mold fungus germinating from a sclerotium. Image courtesy J. Venette, North Dakota State University.

 

Soybean plant with symptoms and signs of white mold (a.k.a. Sclerotinia stem rot). Image by C. Bradley.

 

So, what does the risk of white mold look like for 2014?  This is not an easy question to answer.  In general, rainfall has been consistent in the northern portion of the state, which would favor white mold, but recent temperatures in the 80s and 90s have not been favorable.  However, the short-term weather forecast shows cooler temperatures (60s and 70s).  If a cool and wet trend continues throughout soybean flowering, then the risk of white mold will be elevated.

In University of Illinois research trials, some fungicide products have shown efficacy against white mold.  Foliar fungicides will not provide complete control of the disease, but may reduce disease.  The results of University of Illinois trials conducted in 2009, 2010, and 2013 are shown in Tables 1-3.  Note that some of the more popular, frequently marketed fungicides are not listed in the tables since many do not have white mold on their label because of no to poor efficacy.  In these trials, the primary targeted growth stage to apply foliar fungicides was at R1 (beginning flower).  In some cases, R1 may occur before canopy closure.  If this is the case, then an application at canopy closure (rather than R1) might be more effective in protecting against white mold.  Also note that some treatments in these research trials were applied twice during the season.

 

Table 1. Results of soybean foliar fungicide research trials focused on white mold conducted in 2009 at the University of Illinois Northern Agronomy Research Center (DeKalb County).

Treatment Rate/A Incidence (%) 

8-11-09

Incidence (%) 

9-14-09

Yield (bu/A)
Untreated check 75 95 24
Topsin 4.5 L 20 fl oz 43 96 24
Proline 3 fl oz 38 95 24
Domark 5 fl oz 68 98 23
Cobra herbicide 12.5 fl oz 15 51 42
Omega 1 pt 23 80 34
Endura (2x)* 8 oz 38 86 39
Aproach (2x)* 8 fl oz 35 80 40
LSD 0.05** 33 15 8

*All treatments were applied at the R1 growth stage (July 20, 2009).  Treatments followed by “(2x)” were applied again 9 days later.

**Least significant difference (alpha level = 0.05).  Treatment values that differ by this number can be considered significantly differ from one another.

 

Table 2. Results of soybean foliar fungicide research trials focused on white mold conducted in 2010 at the University of Illinois Northern Agronomy Research Center (DeKalb County).  Funded in part by the Illinois Soybean Association.

Treatment Rate/A Incidence (%) 

8-11-09

Incidence (%) 

9-14-09

Yield (bu/A)
Untreated check 18 95 62
Topsin 4.5 L 20 fl oz 9 83 61
Proline 3 fl oz 10 89 66
Domark 5 fl oz 7 76 63
Cobra herbicide 6 fl oz 6 86 56
Omega 1 pt 2 70 58
Endura 8 oz 4 79 69
Aproach (2x)* 8 fl oz 11 79 66
LSD 0.05** 11 NS 8

*All treatments were applied at the R1 growth stage (July 10, 2010).  Treatments followed by “(2x)” were applied again 7 days later.

**Least significant difference (alpha level = 0.05).  Treatment values that differ by this number can be considered significantly differ from one another.  “NS” indicates that no treatments were significantly different from each other.

 

Table 3. Results of soybean foliar fungicide research trials focused on white mold conducted in 2013 at the University of Illinois Northern Agronomy Research Center (DeKalb County). Treatments were applied at the R1 growth stage unless indicated otherwise.

Treatment Rate/A Incidence (%) 

9-19-13

Yield (bu/A)
Untreated check 33 53
Incognito 4.5F 20 fl oz 20 68
Incognito 4.5F + Orius 3.6F* 20 fl oz + 4 fl oz 0 62
Proline + Stratego YLD** 3 fl oz + 4.65 fl oz 3 58
Domark 5 fl oz 3 62
Cobra herbicide 6 fl oz 25 52
Endura 8 oz 3 64
Aproach 8 fl oz 13 61
Fortix 5 fl oz 15 56
LSD 0.05*** 22 7

*Incognito was applied alone at the R1 growth stage and was followed by Orius applied alone at R3.

**Proline was applied alone at the R1 growth stage, and was followed by Stratego YLD applied alone at R3.

***Least significant difference (alpha level = 0.05).  Treatment values that differ by this number can be considered significantly differ from one another.  “NS” indicates that no treatments were significantly different from each other.

Overall, the highest level of white mold control will be achieved when several management practices are integrated (i.e. choosing the most-resistant varieties, utilizing recommended seeding rates, applying a foliar fungicide, and applying a biocontrol product).  For more information about white mold and management of this disease, go to http://www.soybeanresearchinfo.com/pdf_docs/WhiteMold_NCSRP.pdf, where a 7-page publication on white mold (developed in 2011) can be downloaded.


July 15th Field Day at University of Illinois’ Research Center in Monmouth

The program is set for the 33rd annual University of Illinois’ Northwestern Agricultural Research Center Field Day. The program will begin at 8 am on Tuesday, July 15th.

Buses will carry members of the public to different stops in the research center where campus-based specialists or Extension personnel will present the results of crop and pest management research and current recommendations.

Topics and speakers will include:

  • Stewardship of dicamba and 2,4-D resistant soybean Mark Bernards—Assistant Professor of Agronomy, Crop Science, and Weed Control, Western Illinois University
  • On-Going Concerns Regarding Corn Rootworm Resistance to Bt Hybrids—Mike Gray— Extension Entomology Specialist, University of Illinois
  • Palmer Amaranth: Coming (Soon) to a Field Near You—Robert Bellm—Extension Educator, Commercial Agriculture, University of Illinois
  • Do Soybeans Need Fertilizer N? —Emerson Nafziger—Extension Crop Production Specialist, University of Illinois
  • Unmanned Aerial Vehicles: Sky High Scouting—Dennis Bowman—Extension Educator, Commercial Agriculture, University of Illinois

The Northwestern Illinois Agricultural Research and Demonstration Center is a 320 acre facility, established in 1980, 1 mile North and 4 miles West of Monmouth at 321 210th Avenue. Each year, more than 50 different projects are conducted by up to 12 campus-based project leaders and the center superintendent.

For more information about continuing education units to be offered visit the Hill and Furrow Blog or the Northwestern Illinois Agricultural Research and Demonstration Center website.

If you need a reasonable accommodation to participate in this program, please contact Angie Peltier (309) 734-5161, apeltier@illinois.edu.


Call for Grain Samples

There is some evidence that the “book values” that we have used for many years to calculate the amount of P and K removed by grain during harvest may no longer be accurate for the crops we produce today. The economic and environmental advantages of matching crop removal to replacement with fertilizer nutrients makes it important to have good removal numbers.

With funding from the Nutrient Research & Education Council (NREC) we are starting a new project in 2014 to try to get a better idea for how much nitrogen (N), phosphorus (P), and potassium (K) are contained in harvested grain of corn, soybean, and wheat. This seems like a simple thing to measure, but we expect that things like yield level, soil, crop variety, and growing season weather affect may nutrient levels. Thus we will need to sample widely in order to get a handle on removal.

We hope to get most of the grain samples we need to do this from individual producers across Illinois, with samples sent right out of the field or when grain is stored or delivered to the elevator. We’re starting now in hopes of kicking this off with wheat samples.

We will make it as painless as possible to send in samples, following the procedure below:

1. Before harvest or at the time grain is stored or moved, the cooperating producer will send an email to NPKremoval@gmail.com to request a mailer. The email only needs the cooperator’s name, mailing address, and what grain (wheat, corn, or soybean) is being sent in. If the mailing address is in a different county than the field the sample comes from, please indicate what county the sample will be from.

2. Prepaid mailers will be sent to the cooperator. The mailer will include a plastic sample bag with a label that has the cooperator’s name and crop, and will have only a blank to fill in with the yield level (estimated or measured) of the field from which the sample came (or will come.)

3. The sample bag is sized to hold about 6-8 oz. of grain, which is all we need. The grain should be dry (at or below standard moisture) so it keeps well during shipping. Simply put the bag with grain into the mailer and drop it into the US mail. It will be addressed to go to a lab for analysis.

While we are hoping for a lot of cooperators, sample numbers will be limited by the funds available. That may mean limiting samples from an area where a lot of people volunteer to send samples. If a local elevator would like to send samples from trucks coming to unload, that would work, but would mean recording names, addresses, and yield levels at the point of collection. We would appreciate having seed company or other ag retail personnel encourage individual producers to take part.

Results will be summarized by region, with no identification of individual cooperators. We hope to collect samples over 2014 and 2015, and hope by getting a large number of samples to be able to see how much variability there is in removal numbers and to generate better removal numbers for Illinois producers.

Please email me if you have any questions about this.


Wheat scab rearing its ugly “head” again in 2014

Head scab of wheat (a.k.a. Fusarium head blight) is showing up in the southern portion of Illinois.  In many cases, incidence is moderate to high (over 50% of the heads affected).  Affected wheat heads will appear “bleached” in color.  Heads often are partially affected, with both healthy green and affected bleached areas being present in the same head.  Although I have not been in all wheat production areas in the state, my general observations are that fields in southern Illinois (south of Interstate 70) range from a moderate to high incidence of scab.  The differences in scab incidence from field to field likely are due to differences in susceptibility of the varieties planted, application or no application of fungicides, and local weather.

Wheat field affected by head scab (Fusarium head blight). Note the "bleached" heads. (Photo by Carl Bradley)

Wheat growers may want to evaluate the level of scab in their fields.  It is easiest to observe this disease before heads completely mature.  Growers with moderate to high levels of scab should consider making adjustments to their combine that would allow low test-weight, scabby kernels to be blown out the back of the combine.  Recent research conducted at the Ohio State University indicated that adjusting the combine’s fan speed between 1,375 and 1,475 rpms and shutter opening to 90 mm (3.5 inches) resulted in the lowest discounts that would have been received at the elevator due to low test weight, % damaged kernels, and level of the mycotoxin deoxynivalenol (DON; vomitoxin) present in the harvested grain (Salgado et al., 2011).

 

Wheat head affected by scab (Fusarium head blight). (Photo by Carl Bradley)

Reference:

Salgado, J. D., Wallhead, M., Madden, L. V., and Paul, P. A. 2011. Grain harvesting strategies to minimize grain quality losses due to Fusarium head blight in wheat. Plant Disease 95:1448-1457.


Nitrogen in Late Spring 2014

The corn crop in Illinois is off to a good start in many fields, and in most areas is in the V5 to V8 growth stages, just starting its rapid growth phase. On average, the crop under good conditions will add some 200 lb of dry matter per acre per day over the next 80 days or so. It will take up 3-4 lb per day of nitrogen before pollination, after which the N uptake rate will slow.

The spring of 2014 has not been a wet one overall in Illinois. But as usual, rainfall has been very unevenly distributed; some areas have received 6 inches or more over the past month. In the wetter areas, getting sidedressed N applied has been challenging, and some who applied the full amount of N are concerned about how much might have been lost.

Low temperatures through the winter and into early April helped preserve fall-applied N and the small amount of residual N left after last year’s big crop. April and May temperatures were normal to a little above normal. Maximum soil temperatures 4 inches deep under bare ground reached the mid-70s by mid-May, and into the 80s during the warm periods in late May and early June.

Soil temperatures in the 70s and 80s increase activity of soil microbes, both those responsible for mineralization (release of plant-available N from soil organic matter) and those that convert ammonium (NH4+) to nitrate (NO3). Table 1 has results from six Illinois fields sampled for N in May by Dan Schaefer of the Illinois Council for Best Management Practices (C-BMP) under the N-Watch® program. These results confirm that N loss was not been excessive by mid-May, and also that much of the fall-applied N was in the nitrate form by May. The fact that more N was recovered than had been applied is not unusual; mineralization and carryover N contribute to the amount that’s there.

Table 1. Amounts of N recovered from Illinois fields following application of a variety of N forms, rates, and timings. Sampling took place in early to mid-May 2014. Data from Dan Schaefer.

While many soils are moist or even wet, the threat of N loss is far higher where water has stood, or is standing, than where water didn’t stand for more than an hour or two. The heavy downpour that brought 3+ inches of rain to parts east central Illinois on May 21 left a lot of standing water, but by 12 hours later, much of it had run off the fields. This indicates two things: 1) rainfall rate exceeded the infiltration rate, so less water entered the soil than fell on the soil in most places of many fields; and 2) standing water affected a relatively small percentage of the soil surface.

Where water stands long enough – typically 3 to 4 days at warm temperatures – for the crop to begin to lose some of its green color, that’s a signal that soil oxygen is becoming depleted. Two negative consequences of lack of oxygen are: 1) the start of denitrification (conversion of nitrate to gaseous forms of N) and N loss; and 2) the beginning of root damage, some of which may be permanent. Most of those fields have recovered well.

We can assume that most fertilizer N is by now in the nitrate form, though some of that applied as sidedressed NH3 or (to a lesser extent) as sidedressed UAN may still remain as ammonium. This is typical for mid-June, and it means that the N is subject to denitrification and, in lighter-textured or tile-drained soils, to moving out of the rooting zone.

Measuring N loss from wet soils is not very practical, especially while it’s still wet. Previous work has shown that, at soil temperatures in the 70s, as much as 7 or 8 percent of the nitrate present can be converted to gas and be lost for each day the saturated conditions persist. Conversion rates may be lower than this with lower temperatures deeper in the soil and at night, if some of the N is still in the ammonium form, and if soils still have some oxygen present. So denitrification losses may be less than expected in some fields. And if plants are badly damaged by saturated soils, loss of N may be a smaller problem than the loss of yield potential from plant damage.

It’s rare that whole fields remain saturated for days, so in most fields, the risk of N loss by leaching or through movement out of the field through field tiles is greater than the risk of loss by denitrification. Tiles began running relatively late this spring, which helped keep N in the fields. The first water to reach the tiles came, in many fields, from rainfall before the N was all converted to nitrate, or from before N had been applied, so may have carried relatively little nitrate. But by June, it’s not unusual for water from field tiles to have nitrate-N levels of 10 to 20 parts per million. At 15 ppm N, one acre-inch of water leaving the field carries with it about 3.8 lb of N.

In fields where all of the N has been applied (especially if some was applied in the spring as NH3), where crop color has remained or returned to healthy green, and where there is no standing water now, it’s reasonable to assume that it’s not necessary to add more N. In fields where all of the N has been applied but where water stood long enough to have the crop lose much of its green color, adding supplemental N will increase yield only if plants can grow enough new roots to take advantage of the added N. Chances of such recovery are much greater when the water comes in early vegetative growth like it did this spring (so far, at least) than when it comes later.

In fields that still need sidedressed N, or where plants stood in water to the point of turning pale green but now seem to be recovering, N should be added as soon as practicable. The easiest way to apply N to wet fields is as urea (with a urease inhibitor such as Agrotain® added) applied by air, but that’s also costly. Waiting until high-clearance equipment can get through to apply broadcast urea with urease inhibitor or UAN (also with urease inhibitor, especially if rainfall is likely to be delayed) using drop tubes is usually cheaper, but may require days or weeks to dry out enough.

The amount of supplemental N – that applied to make up expected loss after a full rate was applied – should generally not exceed 50 lb of N or so. If a planned sidedress application is made late, plant uptake will start quickly, reducing the time available for loss. That may allow the rate to be lowered from what had been planned, especially if the planned rate would have brought total N to the higher side of guideline rates.

While it’s good to apply supplemental N (if it’s needed) or planned sidedressed N as soon as we can, the yield cost of further delays depend on the N available to the plant now. The best way to know how much N is available to the crop now is to observe canopy color; as long as leaves remain a reasonable shade of green, the plant is not deficient, or not deficient enough to cost yield as long as final N supply is adequate. In that case, some delay in applying N may not cost any yield. If it turns dry after surface application of N, uptake will be delayed and the risk will increase of having the crop run out of N.

Putting all this in perspective, the 2104 season has not been one of above-average N loss potential, except in areas that were unlucky enough to get big downpours. Remember that mineralization of soil organic matter is contributing substantially to the N supply in the soil now, helping to counter some N loss from tile lines. This is not the case in saturated soils, where mineralization is slowed as denitrification speeds up.

Still, if good rainfall and temperatures continue, the N supply, even if it’s reduced some by loss, is unlikely to limit yield. In fact, most of the highest yields we have seen in several hundred N rate trials over the last 20 years have come at modest N rates. I think this happens because good root systems mean good uptake of water and N, and that conditions that are ideal for yield also tend to be very good for soil N supply.


Another Look at Soybean Planting Date

Soybean planting is off to a mediocre start in Illinois, with 26% of the crop planted by May 11, and limited progress with the rain of this past week. Planting will resume in some places this week, but other areas remain wet and it will take some time for soils to dry out. In comparison with recent history this is not yet a serious delay, but as time passes the delay will become a bigger concern.

Over the past four years we have conducted studies that, among other things, have compared yields of soybeans planted over a range of dates, from mid-or late April (or when conditions allow) into early to mid-June. This research was funded by the Illinois Soybean Association.

We were unable to produce useful data from most southern Illinois sites due to the late start in many cases, and poor stands in others. This demonstrates little other than that late starts are quite common in southern Illinois, and that poor stands are not more common from early planting than from late planting. Instead, poor stands almost always result from heavy rainfall soon after planting, regardless of when the crop is planted.

I combined data from 15 site-years (not including Perry in 2012, where yields were every low) in central and northern Illinois, with yields at each site-year calculated as percent of the maximum yield for that trial. Figure 1 shows the overall response to planting dates over these sites. The average maximum yield across all trials was 66.2 bushels per acre, so each percentage point is about 3/2rds of a bushel.

Figure 1. Response of soybean yield to planting date over 15 Illinois site-years, 2010-2013.

Based on these numbers, a delay to May 20 means yields on average about 10% less than maximum. From May 20 to the end of May, the drop is about 0.5 % per day of delay. From June 1 to 10, it is about 0.6 % per day. The cumulative loss by June 10 is about 20%.

While Figure 1 shows the best prediction we have for planting date in Illinois, the curve doesn’t tell the whole story. When we look at yield data from separate trials, we find that there seem to be two lines – one for trials where yields are high and one for trials where yields are lower (Figure 2).

Figure 2. Soybean yield response to planting date over 15 Illinois site-years, divided into higher- and lower-yielding sites.

Because we typically don’t know what yield level will be, data presented as in Figure 2 don’t provide a better prediction of yield loss than Figure 1. Rather, they simply show that when something other than planting date limits yield, planting date becomes less important as a factor that influences yield.

As I said about corn planting date in an earlier article, having planting delayed by wet weather past a certain date – May 15 or 20 for soybeans – does not rule out getting high yields. But we still want to plant as soon as we can in order to have plants take better advantage of growing conditions that should continue to improve starting soon.


Considerations for fungicide management of Fusarium head blight of wheat

Wheat plants are now beginning to head out and flower in parts of southern Illinois. During this critical time of wheat development, wheat becomes susceptible to infection by Fusarium graminearum, the causal agent of Fusarium head blight (FHB; also known as scab) (Fig. 1). This disease can cause reduced grain yield, test weight, and quality. In addition, the fungus can produce toxins that will contaminate grain such as deoxynivalenol (DON; also known as vomitoxin). Harvested grain with high levels of DON may be discounted or outright rejected at the elevator. To achieve the best management of FHB, different management practices must be implemented, such as planting wheat into fields that were previously cropped to soybean (rather than corn), planting wheat varieties with moderate to high levels of resistance to FHB, and applying foliar fungicides at the proper timing. Of these different management practices, the application of foliar fungicides is the only one that can be done during the growing season and is the main focus of this article.

Fig. 1. Symptoms of Fusarium head blight (scab) of wheat (note the “bleached” heads).

Multiple fungicides are registered for use on wheat, but only a few have efficacy in managing FHB. Fungicides available for FHB management all belong to the triazole class of fungicides and are Caramba (BASF Corporation), Prosaro (Bayer CropScience), Proline (Bayer CropScience), and products that contain tebuconazole as their solo active ingredient. Of these products, the best efficacy has been obtained with Prosaro and Caramba in multi-state university field research trials. Proper fungicide application timing is critical in achieving the best efficacy. The best application timing is considered to be when plants are beginning to flower (early anthesis – Feekes growth stage 10.5.1), but some efficacy may still be achieved slightly before or after Feekes 10.5.1 (Table 1). In regards to fungicide application timing, it is important to always follow the label recommendations and consider the preharvest interval (PHI) requirements (PHI for Caramba, Prosaro, Proline, and tebuconazole products is 30 days). Fungicide products that contain strobilurin active ingredients should not be applied for control of FHB, and most do not list FHB control or suppression on their label. In multiple university research trials, strobilurin fungicides have been shown to increase DON levels in grain compared to non-treated checks. Therefore, it is extremely important that only effective triazole fungicides be applied for management of FHB.

Table 1. Effect of fungicide application timing on Fusarium head blight (FHB) control in wheat. Results represent data collected from Dixon Springs, IL in 2009, and Brownstown, IL, Carbondale, IL, Dixon Springs, IL, and Urbana, IL in 2010.

Fungicide

Application timing

FHB (% control)*

Prosaro @ 6.5 fl oz

Feekes 10.5

35 b

Feekes 10.5.1

59 a

5 days after Feekes 10.5.1

37 b

Caramba @ 13.5 fl oz

Feekes 10.5

38 b

Feekes 10.5.1

61 a

5 days after Feekes 10.5.1

36 b

*Values followed by the same letter in the table are not significantly different with 95% confidence.

When making a decision on if a fungicide application is needed, FHB risk should be assessed. A FHB Prediction Tool is available on-line at www.wheatscab.psu.edu. This risk is based on weather conducive for FHB, and should be assessed for each field as they begin to develop heads in anticipation of flowering. On May 9, 2014, a LOW risk of FHB was present in all of Illinois; however, this status can and will change depending on weather conditions. Therefore it is important to continually monitoring the FHB Risk Prediction Tool as more and more wheat fields get closer to the flowering stage.


Another Look at Corn Planting Date Response

As we head into May, Illinois is ahead of most of the rest of the Corn Belt, with 32% of the corn crop planted here by April 27, close to the 33% that was planted by that date averaged over the past 5 years. Only 19% of the US corn crop was planted by April 27, and states to the north and east of Illinois were in single digits. It is wet in much of the Corn Belt now, and further delays are expected.

We’ve been running planting date studies for a number of years at a number of sites in Illinois. While there’s always a lot of variability in planting date responses, we do have data sets that combine well – where there is some consistency over years and where yield levels were not wildly variable. One such set is from DeKalb and Monmouth over the past seven years – 2007 to 2013 (Figure 1). Data from several years at these sites were used to develop the corn replant model in the current Illinois Agronomy Handbook. These sites also represent the Corn Belt quite well, so results are applicable over a wide area.

Figure 1. Response to planting date combined over seven years (2007-2013) and two sites in northern Illinois.

Combining data by percentage of maximum yield for each site and year shows that highest yield comes at about April 20 (Figure 1). This is similar to what we’ve seen as the “best” planting date in most recent planting date summaries. But yield penalties from planting delays are somewhat milder here than we have previously reported. Compared to the highest yield (on April 21), the yield loss for planning on April 30 was 1% (2 bushels); by May 10 it was 4% (8 bushels); by May 20 it was 8% (17 bushels); by May 30 it was 14% (29 bushels); and by June 10 the total yield loss predicted from these data was 22%, or 49 bushels per acre.

The average maximum yield across all sites was 216 bushels per acre. Losses measured as bushels per acre per day of delay, for 10-day periods starting on May 1 were:  May 1-10 (0.6 bu/acre/day); May 10-20 (0.9); May 20-30 (1.2); and May 30 to June 10 (1.9). Thus the loss accelerates, with more loss per day of delay the later it gets. Because average temperatures rise during April and May, the per-GDD yield loss would accelerate less than the per-day loss – it would be closer to a straight line.

These results bring up an obvious question: has the planting date response really changed, or are we just looking at a “favorable” set of data? That’s not completely clear, but I do think that increasing tolerance to the stress of high populations has likely helped plants to also do better under increased weather-related stresses, especially during pollination, that are more likely with late-planted corn than when the crop is planted early. Seven years is a reasonable “sample” of years, and these results weren’t only the product of what happened in one or two “odd” seasons.

One lesson we certainly can take from this is that having planting delayed to early or mid-May does not mean “game over” in terms of yield potential. Average GDD accumulations during April range from less than 200 in northern Illinois to about 300 in southern Illinois, and amount to less than 10% of the seasonal total. In other words, losing April doesn’t greatly diminish how much season is available to produce a crop. The main reason why late planting lowers yield is due to the increased chance of water stress when pollination is delayed.

The April 1-planted corn in our planting date study here at Urbana is at the 1-leaf stage now, and not looking great with night temperatures around 40 and daytime highs in the 50s this week. Plots planted on April 1 at Perry froze before emergence, and will have to be replanted. So this year, early planting didn’t get the crop very far ahead.

Our hope now is that temperatures will start to rise and will remain at least as high as average through May. This will help both to dry the soil after rain and the crop to take off once we get it planted. But as much as we hope we can finish planting within the next couple of weeks, rain in July will, as usual, be the main thing we’re going to need for good yields in 2014.


Running On-Farm Strip Trials

On April 16 I posted an article http://bulletin.ipm.illinois.edu/?p=1966 on the use of nitrogen fertilizer on soybean, mentioning at the end of the article that this would be a good thing to test in on-farm trials. Here I’ll provide a little background and a brief description of how to go about doing such a trial.

Background: dealing with variability

If there were no variability in yields (or soils) going across a field, a single strip of N fertilizer (or without N while applying N to the rest of the field) would measure the effect. There is no such field: every strip will yield at least a little more or less than every other strip in every field. So a single strip where we might plan to apply N fertilizer will always yield differently than the strip next to it, and we can never be sure if any “difference” we see in yield was due to treatment or just to this “random” variability, with one or another treatment just “lucky” in getting assigned by chance to higher-yielding strips.

One way we deal with this variability is to locate trials in the most uniform part of the field we can find. This can never eliminate variability between strips, but it minimizes it. Using a yield map from a previous year can help find areas in the field where there is good uniformity. If a map of a given field doesn’t show an area large enough for a trial with good uniformity, consider moving the trial to a different field. If strips need to be shorter than the field in order to avoid a variable area, it’s OK to do that, as long as good yield measurements are possible.

The only way we can measure and deal with the strip-to-strip variability in a field is to replicate treatments – that is, to apply the same treatments to a number of different strips. The variability among yields of strips treated the same tells us how variable yields are, and we then use stats to help us figure out if yield differences between treated and untreated strips are probably due to treatment or could easily be due to random variability and chance placement of treatments.

If we can’t be sure that a difference is due to treatment and not just to random variability, then we have to conclude that we haven’t proven that the difference is due to treatment, and we say the difference is “not significant.” This doesn’t mean the treatment did nothing, it just means that we haven’t proven to our satisfaction (that is, to a probability level of 90 or 95%) that it did. By the same token, a treatment that does nothing at all can get “lucky” and end up on higher-yielding strips by chance, producing a “significant” difference that was really no difference at all.

Running a strip trial

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

  1. 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 for the 4 corners of the area, 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.
  2. Assign treatments to strips randomly within each pair of strips. Here is how this might look:
  3. 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
  4. Apply in-season N to the strips where it was assigned. Timing and form are not fixed, but I suggest using 50 to 80 lb of actual N (120 to 200 lb urea 45-0-0 or similar; protecting with a urease inhibitor and using slow-release urea in the mix are good options) applied between stage R4 (full flower) and R6 (full seed). Liquid (UAN) can be injected, but dry forms are most common and easiest to apply in plants this size. If you drive down strips to apply by ground, and there’s a possibility that this will do some damage, you’ll want to drive (with applicator off) down the “No N” strips as well so all strips experience the same thing. N can be applied by air, but 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.
  5. Harvest and record yields for each strip. Be sure that the width harvested is the same for each strip, and trim the ends if using yield monitor data.
  6. Average yields with and without N to see if there are differences. Do a statistical analysis, or work with an adviser to do so. If you wish, you can send me yields on a spreadsheet and I’ll return it with stats run and a note about the outcome. If you do your own analysis, I’d much appreciate getting the data so we can look at this across all sites.

Doing such trials in different soil types – especially in soils with different textures and amounts of organic matter – will help show whether or not an N response is affected by soil. Some may want to do trials in more than one field, or to cooperate with neighbors to do this. For questions like this, the more data, the better.