Corn imbibitional chilling: Fact or fiction

For the first 24-48 hours after dry corn seed is planted into the ground, all that takes place is physical imbibition of water into the seed. Water and oxygen move slowly into the kernel through the seed pericarp. Membranes re-hydrate and hormones and enzymes are activated. After the seed swells, enzymes begin to breakdown starch in the endosperm. Sugars supply the embryo with energy for metabolism and cell division.

Imbibitional chilling occurs when membrane re-hydration is disrupted by free radicals before the seed finishes swelling. Cold water is much more disruptive than warm water. Sugars and salts leak from the cells and kernel providing a food source for pathogens and other microbes. It becomes a race for the plant to emerge or death from pathogens.

One of the most dramatic examples of imbibitional chilling occurs with sweet corn. In a study conducted by Bill Tracy (2005), untreated seed of six supersweet corn varieties were exposed to three treatments. Each treatment consisted of one 24-hr period at 40 F temperature and five days at 75 F. Seed was placed in rag dolls with no soil. 

Sweet corn seed has a wrinkly seed pericarp with numerous cracks, fissures and potential endosperm leakage sites. In this study, most seed death occurred within the first 24 hrs (day 1) of being exposed to 40 F (Figure 1). Significant variety differences for the amount of seed death were observed. Significantly less seed death was occurring when exposed to 40 F on days 2 and 3, and no seed death when exposed to 40 F on day 4.

Figure 1. Six supersweet corn varieties exposed to one 24 h period at 40 F and five days at 75 F. Click to enlarge.

There is considerable debate about what specific temperature and timing causes imbibitional chilling in field corn. Field corn seed does not have the pericarp cracks and fissures that sweet corn has. One current recommendation is to begin planting corn when soil temperatures are in the high 40s and the short-term forecast calls for warm days that will continue pushing soil temperatures higher. If soil temperatures are in the high 40s and the weather forecast calls for cold wet conditions within the next 48 hours, soil temperatures will likely drop and planting should be delayed until temperatures warm.

That recommendation is simply not our experience in Wisconsin and likely the northern tier of U.S. states. If we waited to plant until soil temperatures were above 40 to 50 F we would need to wait until mid May in many years (Table 1). It only gets later as we move north. Yet, our highest yielding planting dates are in late April and early May.

Table 1. Last date when the minimum soil temperature at the two-inch depth was below 40 F and 50 F at Arlington, WI. Click to enlarge.

The only time I thought our UW Corn Hybrid Trial plots had been affected by imbibitional chilling was during 2006 at Seymour, WI (Figure 2). I happened to be along on that planting trip. It began to snow after we had finished planting and continued to be cool and wet for the next 72 hrs. We went back to the field a few weeks later and unbeknownst to us at planting, found that the field had shallow swales and a drainfield. Corn emergence was perfect over the drainfield and on the ridges of the swales. However, much plant death occurred between the drainfield spurs and swale depressions. We did not observe standing water, although it could have been another possible reason for plant death. We abandoned the trial due to stand variability.

Figure 2. Daily air temperature and precipitation at during 2006 at Seymour, WI. The red arrow indicates when the UW hybrid trial plots were planted. Click to enlarge.

Our current recommendation for beginning to plant corn seed is, "In southern Wisconsin, plant corn anytime after April 20, if the field is 'fit', and after April 30 in northern Wisconsin." If the short-term forecast is for cold temperatures and snow/rain, then the prudent thing to do is hold-off planting. We have available excellent seed treatments that can protect the seed for the first 30 to 45 days after planting.

This advice we use to plant and establish the UW hybrid trials at 14 locations around the state. We have often had snow on our plots with no establishment and emergence issues. For the last 5 years we have planted a few hundred feet of four hybrids beginning in March and then every 2-3 weeks - we do this to get the planters out and tuned. We do see hybrid differences and in only one case did we see emergence issues for all four hybrids. Remember that insurance coverage does not begin until planting dates after April 10.

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Corn grain yield response to crop rotation during odd growing seasons

Earlier this week we looked at corn grain yield response to crop rotation in extreme growing seasons when both Growing Degree Unit (GDU) accumulation AND precipitation were abnormal (click here). In extreme growing seasons, crop rotation was the best treatment while continuous corn was impacted more than during average growing seasons. I was asked a follow-up question about the crop rotation effect on grain yield when growing seasons were "off" for GDU accumulation OR precipitation. Again, data from the 35-yr corn-soybean rotation experiment conducted during 1987 to 2021 at Arlington, WI was used for the analysis.

Odd GDU accumulation years were selected when a growing season was + one standard deviation from the average (Figure 1). Cooler seasons included: 1992, 1993, 1997, 2004, 2008, 2009, 2013 and 2014. Warmer growing seasons included: 1987, 1988, 1991, 1995, 2005, and 2021. Grain yield during an average GDU growing season was 195 bu/A. Warm seasons averaged 170 bu/A, and cool seasons averaged 171 bu/A.

Figure 1. Corn grain yield response to growing season Growing Degree Unit (GDU) accumulation during 1987 to 2021 at Arlington, WI. Years were selected and grouped when GDU accumulation was + one standard deviation from the average. Click to enlarge.

Likewise,  odd precipitation years were identified  when a growing season was + one standard deviation from the average (Figure 2). Drier growing seasons included: 1988, 1989, 2003, 2005, 2011, 2012, and 2021. Wetter growing seasons included: 1993, 2006, 2008, 2010, 2018, and 2019. Grain yield during an average precipitation growing season was 188 bu/A. Grain yield during dry seasons averaged 166 bu/A, and during wet seasons averaged 178 bu/A.
 

 

Figure 2. Corn grain yield response to growing season precipitation during 1987 to 2021 at Arlington, WI. Years were selected and grouped when precipitation was + one standard deviation from the average. Click to enlarge.

The key point is that crop rotation maximizes corn grain yield consistently regardless of the kind of growing season. As a cropping sequence becomes more continuous, corn grain yield is more affected by odd growing seasons compared to an "average" growing season whether cool/warm or dry/wet. Grain yield in the second corn year following five years of soybean (2C) is more affected in a warm growing seasons than 2C in cool or dry/wet growing seasons. By 3C, the rotation effect is gone and grain yield are similar to 35+ years of continuous corn.

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Farmers continue to increase corn plant density

As technologies improve over time, management decisions need to be adjusted to keep up with the changing times. Better equipment, improved bio-engineered hybrids, better seed treatments, irrigation technologies, new pesticides, etc. have all contributed to corn grain yield progress. One management decision that continues to evolve is plant population. For some recent articles on this topic click here and here. For the latest USDA-NASS data collected in farmer fields during August, see Figure 1. Field plant populations are increasing at the rate of 270 to 300 plants/A*yr. Usually about 5 to 10% of the seed planted does not emerge, so seeding rates are 31,000 to 35,000 seeds/A.

Figure 1. Corn plant density changes over time for selected U.S. states. The rate of change (slope) in plants/A*yr since 1982 is reported for each state. Data derived from USDA-NASS (1982-2021). Click to enlarge.

It is clear from our research data that maximum yield plant densities (MYPD) and economic optimum plant densities (EOPD) are increasing. Recent research has shown that each hybrid has a MYPD and EOPD. There is gathering evidence that even each field within a farm may have a corn MYPD and EOPD. In many years (not 2022), seed cost can be as big of an input cost as nitrogen cost (Figure 2). Input adjustments can mean significant cost savings when corn grain prices are low (again not 2022).

Figure 2. USDA-ERS cost of production estimates for corn (last updated October 1, 2021). The Northern Crescent includes the northern tier of U.S. states along the Great Lakes. The Heartland includes Midwest Corn Belt states. Click to enlarge.

Adjusting plant density for your fields is one of the key production decisions for producing high yielding corn. Clearly farmers are adjusting plant densities higher. One approach to adjusting this decision is to plant the majority of your field to a target plant density based upon your experience. Then for one round (or pass) in a couple parts of the field, increase plant density 10%. Measure yield at the end of the season and during the season watch for "runt" plants, tillering, prolificacy, ear bareness. big versus small ears, ear tip "nose-back" and plant lodging. Adjust the field accordingly the following year.

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Corn grain yield response to crop rotation during extreme weather

 

The 2022 growing season started out with drought concerns and now wet, cool weather conditions make many wonder when we will ever get into the field. I have been curious about how well some of our agronomic recommendations hold up in extreme weather conditions. Let's review what happens with the crop rotation recommendation where we encourage farmers to rotate crops when possible. I will use data from a corn-soybean rotation experiment that was initiated in 1983 at Arlington, WI.

The first four years of this experiment were "set-up" years for the crop rotations and were discarded from the analysis below. So that leaves data collected during the 35-yr period from 1987 to 2021. Extreme growing degree unit (GDU) accumulation years were selected when a growing season was + one standard deviation from the average. Cooler seasons included: 1992, 1993, 1997, 2004, 2008, 2009, 2013 and 2014. Warmer growing seasons included: 1987, 1988, 1991, 1995, 2005, and 2021. Likewise,  extreme precipitation years were identified  when a growing season was + one standard deviation from the average. Drier growing seasons included: 1988, 1989, 2003, 2005, 2011, 2012, and 2021. Wetter growing seasons included: 1993, 2006, 2008, 2010, 2018, and 2019. The growing seasons that were most extreme for both GDU accumulation AND precipitation were: Cool/Wet= 1993 and 2008; and Warm/Dry= 1988, 2005, and 2021. All other growing seasons were lumped into average years for producing Figure 1.

Figure 1. Relative corn grain yield (percent of maximum) of various cropping sequences following soybean during 1987 to 2021 at Arlington, WI. Cool/Wet and Warm/Dry growing seasons were determined by selecting years + one standard deviation from the average for both growing degree unit accumulation AND precipitation. Click to enlarge.

For a previous report on grain yield response in this experiment, click here. Corn grain yield during an "average" growing season over this 35-yr time period was189 bu/A. Corn grain yield during "cool/wet" seasons was 179 bu/A and during "warm/dry" seasons was 155 bu/A; both lower than the yield of an average season.

Regardless of the kind of growing season, the best grain yielding treatment was corn following 5-yrs of soybean (1C). Corn in a corn-soybean annual rotation (CS) was the next best rotation treatment and usually not statistically different than corn following 5-yrs of soybean, except in a cool/wet year. Continuous corn (CC) yielded 17% less in an average season than 1C. However, during cool/wet and warm/dry season grain yield was 27 to 28% less than 1C. 

Relative grain yield of second year corn (2C), 3C, 4C, and 5C was lower in cool/wet and warm/dry growing seasons than an average year. In an average year, we typically see a yield response for 2C while 3C, 4C and 5C yield similarly to CC. In a warm/dry season there was no rotation response for 2C compared to 3C, 4C and 5C, while cool/wet seasons still had a yield response in 2C. For all growing seasons, 3C, 4C and 5C do not yield differently than CC.

Although the corn-soybean rotation is the dominant cropping sequence in the Midwest U.S., many Wisconsin farmers add other crops like wheat and alfalfa when possible. I would expect a similar response as above, especially in the second year of the continuous crop. At least two break years from the continuous crop will produce a rotation response in the second year, unless the growing season is warm/dry (i.e. drought). The rotation response disappears by the third continuous crop regardless of the type of growing season.

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Dragging a manure hose over corn at early growth stages does not reduce yield.

Photo by Chris Pfarr

One of my earliest memories of growing corn was driving tractor while picking rocks on my uncle's farm. I was 6 years old and could barely push in the clutch. After getting me going in granny gear and pointing me down the field, my only job was to drive straight and stay off the corn. However, I ran over lots of corn and thought I had caused the death of numerous seedlings that day, but my cousin said not to worry. I don't remember what happened when we reached the end of the field, but I do remember I was demoted quickly from tractor driver and promoted to rock picker.

Running over corn happens when side-dressing with a manure hose application system. However, little is known about what growth stage different corn hybrids can be dragged with a manure hose before plant population and grain yield is affected. In a paper published in Agronomy Journal field studies were conducted in 2019 and 2020 in Minnesota. Plots were dragged in both directions along the row with a manure hose from the first through sixth leaf collar growth stages (vegetative [V] growth stage V1 through V6) and compared to a non-dragged control. Dragging corn at V1 to V3 did not significantly damage the crop. Dragging corn at V5 and V6, and sometimes V4, reduced yield and increased grain moisture. Dragging at V4 reduced plant population and yield by 41% in 1 of 4 site-years, while dragging after V5 significantly reduced yield by 21–79% and in most cases, increased grain moisture. These results suggest that when using a manure drag hose application system to side-dress corn, side-dressing should be completed before V4 to avoid damaging the crop.

Further reading

Wilson ML, Pfarr CJ, Fernández FG, Coulter JA. Dragging a manure hose over corn at early growth stages does not reduce yield. Agronomy Journal. 2021;113:3910–3921.
https://doi.org/10.1002/agj2.20797

Sidedressing Corn: Swine Manure via Dragline Hose Produces Yields Comparable to Synthetic Fertilizer

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Planting date effects on corn grain and forage yield

Corn planters will soon be rolling throughout Wisconsin and the Midwest Corn Belt. The annual struggle between field conditions being "just right" and not too wet versus delaying planting to another day will start to weigh on farmer's minds. In addition, planting delays in the northern tier of U.S. states have greater impact on yield due to a shorter growing season and the added dimension ("double-whammy") of drying costs at harvest that can occur during cool, wet growing seasons. 

Figure 1 shows the impact of planting date on relative grain yield at Arlington. If all corn could be planted on one date, ideally it would be on May 1 or slightly earlier to decrease drying costs. Planting delays to June 1 will lower yields about 30%. However, in some growing seasons, 100% of the maximum grain yield can be achieved planting into late May. Grain yield decreases 0.5 bu/A per day on May 15 and accelerates to 2.5 bu/A per day on June 1.

Figure 1. The relationship between relative grain yield and planting date. Data includes all hybrids and trials conducted between 1991 and 2021 at Arlington, WI. Click to enlarge.

A similar story emerges for corn forage yield (Figure 2). A good rule of thumb is that, "What you do to maximize corn grain yield, you should also do to maximize corn forage yield." The ideal planting date to maximum forage yield is May 1. By June 1, forage yield has decreased about 15%. However, many planting dates in June have achieved 100% of relative forage yield in the past. Forage yield decreases 0.2 T DM/A per day on May 15 and accelerates to 0.3 T DM/A per day on June 1.

Figure 2. The relationship between relative forage yield and planting date. Data includes all hybrids and trials conducted between 1991 and 2021 at Arlington, WI. Click to enlarge.

For both corn grain and forage yield, the variability (i.e. risk - spread of the data points around the average) of June planting dates increases. The success of June planting depends upon the growing season. For example, many farmers had success with June planting in 2021, while few had success in 2019. Now is the time to be ready to go, if field conditions allow.

Seeding depth affects corn plant emergence uniformity and grain yield

Planting depth effect on mesocotyl length. (Click to enlarge)

Rarely do we see a paper published on corn seeding depth and the subsequent impact on grain yield. Precision technologies have allowed for capabilities of variable rate seeding, multi-hybrid planting on the go, and the ability to vary planting depth in real time in response to real-time soil moisture data. In a paper published by Nemergut et al. (2021), corn seed was planted at 1-, 2-, and 3-inch depths on two soil types in Ohio over three growing season (2017 to 2019). Shallow planting resulted in less uniform more extended emergence periods than 2- and 3-inch planting depths. If a plant emerged within 3 days of the first emerged neighboring plants, then there was no effect on plant grain yield. Any plant that emerged more than 3 days after the first emerged plant had a 5% decrease in kernel weight per day. Grain yield per plant increased as planting depth increased. Grain yield per acre was significantly increased by planting depth with seed planted at 2- and 3-inches yielding 8 or 10% more than the 1-inch seeding depth on one of the two soils. Other researchers have also shown improving emergence uniformity can positively increase yield, and that optimum planting depth may vary by field.

Further Reading

Nemergut KT, Thomison PR, Carter PR, Lindsey AJ. Planting depth affects corn emergence, growth and development, and yield. Agronomy Journal. 2021;113:3351–3360.  https://doi.org/10.1002/agj2.2070

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What if the 2022 Growing Season is a Drought?

 

U.S. Drought Monitor map released April 7, 2022. (Click to enlarge)

There is a lot of concern among farmers about dry spring conditions as we head into the 2022 growing season. Significant areas of the western U.S. are encountering extreme to exceptional drought. In the Midwest, the southern tiers of Wisconsin counties and the northern 1-2 tiers of Illinois counties are abnormally dry or under moderate drought.

Figure 1 describes the 30 yr monthly average precipitation at the UW Agricultural Research Station in Arlington. Only 23.5 inches of precipitation was measured during 2021 compared to the 30-yr annual average of 35.2 inches. We typically get most of our precipitation during April, May and June. The variability (risk) of precipitation patterns during April to June is quite high ranging from 3.8 to 5.4 inches (standard deviation= + 1.9 to 2.7 inches). Monthly precipitation amounts can range from 1.8 to 7.9 inches of precipitation during April, May and June.

Figure 1. Monthly precipitation at the UW-ARS in Arlington. Data were derived from the Midwest Regional Climatological Center. Error bars are the standard deviation of the 30 yr monthly average. (Click to enlarge)

During 2021, monthly precipitation was outside of the error bars in Figure 1 only during April and November. Drier conditions during April allowed for early planting, while drier grain moisture was observed at harvest. The month that was average for precipitation was August which is the grain-filling period for corn. No 2021 precipitation monthly average was above the 30 yr monthly average. So even though precipitation was one of the lowest on record, the distribution was adequate for near-record grain yields.

Some of the current drought conditions described by the U.S. Drought Monitor for Wisconsin and Illinois are a holdover from the 2021 season. Since January 2022, the amount of precipitation measured at Arlington is average. Soil profile water content is likely lower than normal. 

How Do We Prepare for the 2022 Growing Season?

The short answer is that you "manage for the average." Don't change things too much unless you have been considering and preparing changes in your management style for some time. The weather during 2022 could be cooler/warmer and/or drier/wetter than normal.

Again, I would "manage for the average" during 2022. No one can predict the weather. If you are convinced that the weather is going to be drier than normal, then I would consider the following:

1. Select a hybrid that is bio-engineered to include drought "tolerant" transgenes. Be wary of hybrids traditionally bred for drought "resistant" traits.
2. Use hybrids with the Bt-ECB bio-engineered trait. Stalk integrity will be important for water molecule movement within the plant and will likely increase standability at harvest. Mycotoxin issues are more often observed in drought stressed years because of increased corn borer activity.
   
3. Select a hybrid that is shorter-season than typical for your field. You will give up yield compared to a full-season hybrid, but the the shorter-season hybrid will go through pollination earlier when soil profile water might be adequate to ensure pollination.
4. Plant early. Planting corn early has the same effect as selecting a shorter-season hybrid. Plants will go through the pollination phase earlier when soil profile water content is greater.
   
5. Lower plant population. Our data shows that grain yield is not affected by plant population during a drought year. By lowering your plant population you capture some return on investment by lowering seed cost.
6. Rotate your crops. Rotated corn grain yield during a drought year is increased (25 to 30%) more than continuous corn. 
7. Use no-tillage. Residue on the soil surface acts as a mulch and a boundary layer for evaporation from the soil surface.
8. Control weeds. Weeds will compete with corn for water resources.
9. Do not over-apply nitrogen. Apply at MRTN rates. Nitrogen increases corn leaf area thereby increasing the potential amount of surface area and cooling load that the plant requires for transpiration.
   

Some of these management decision changes have the potential to leave yield in the field during a normal weather year. As we saw during 2021, some of these decisions are about timing of precipitation events. I remember the 2005 and 2012 when weather conditions were dry through mid-July. Adequate rains came in mid-July and soils that had higher soil water content allowed plants to escape drought effects on pollination. For some, early planting date and shorter-season hybrids did not work and fields were abandoned.

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