Hoegemeyer - the right seed

For many, this spring has not allowed planting to progress as planned and already there have been some comments about when to switch corn maturity.  As of May 1st, there is still plenty of time to get corn planted without having to worry about switching corn maturity.  No matter what date you planted your corn, it still takes about 125 Heat Units or GDU’s for corn to emerge plus research has shown that corn can also adapt GDU needs for growth and maturity if corn is planted after May 1st. 

For example, in an average year, a full season corn that normally needs 2800 GDU’s to reach black layer will adapt by requiring about 6.8 fewer GDU’s per day for every day planted after May 1st.  Factoring the numbers, if a full season 2800 GDU corn was planted on May 15th, it would need about 95 fewer GDU’s to reach black layer (14 x 6.8) because the overall warmer conditions after May 1st will help accelerate emergence time out of the ground plus the first days after emergence will probably have more measureable GDU’s per day after emergence as compared to earlier planting which were more likely cooler days.

There is still a point though that a corn maturity switch might be considered but in general, experts say that date for the Western Corn Belt is between the 20th to 27th of May.  Attached is “Switchybrids”, a 2011 article Tom Hoegemeyer wrote about making corn maturity switch decisions.  I hope this article is helpful for those that may be wondering about switching corn maturities.   

Switchybrids
By Dr. Tom Hoegemeyer – from 2011
 

You have to love farming in the Great Plains—or it will drive you crazy.  We have gone from having a mix of wet areas in a relatively dry region, to being cold and soaked.  And the forecast is for another wet week or more before we will have a chance to get into the field.  We have had several inquiries concerning planting dates for specific hybrids, and when will they need to consider switching hybrids and maturities.

The issue is how many heat units do we have to work with, and how is yield affected by later planting.  First, the total heat unit accumulation from a presumed planting date to the average date of first freeze in the fall is fairly well known for each locality.  If you look at these heat unit tables (on the web or from your university extension group) there, typically, is about 350 heat units accumulated between April 15 and May 15—that is not a lot of growth potential between those planting dates.  Compare the tables of heat unit accumulation from spring dates to first freeze, and the heat unit requirements of your favorite “full season” hybrids in the 2011 Seed Guide.  It is clear that at nearly every location there is likely to be enough heat units to mature our favorite hybrids if they are planted by May 20th.  When it is cold, cloudy and wet (like the predictions) we accumulate few heat units.  If the daily low is 40 degrees, and the high is 60, we average the two temps, and subtract 50, giving zero heat units for such a day—meaning corn isn’t going to grow anyway.  We are likely to lose fewer than 150 heat units if planting is delayed for the next two weeks.  And for each two days later emergence we might see (assuming a two week delay in planting), we will likely delay flowering only one day.
Second, how much is yield affected by a delay in flowering?  For optimum yields, one wants to fill grain during longer days—that is as soon after July 4th as possible.  However, actual yields are GREATLY impacted by heat (and moisture) stress in the period of a week before until 10 days after silking.  Better or worse weather a few days earlier or later makes much more yield difference than precise planting date—and that’s mostly random in mid-July.  However, if flowering is delayed until late July, the odds of hotter, drier weather increase.  Especially in irrigated corn, the “optimum” planting date implies lower yields if planted BEFORE or AFTER the optimum date.  And, historically those optimums lie between April 20 and May 5 for most of us.

Then, there is the issue of hybrid yield potential, by maturity.  Longer season hybrids, in general, always have higher yield potential than earlier ones.  They have greater leaf area—just a bigger factory to produce grain—and greater ear size and/or number of kernels—more room to pack starch and protein.  Switching to earlier hybrids, even if they have high yield potential, almost always results in putting a “lid” on yield potential.  As long as we have enough time (heat units) available to mature the fuller season hybrid, we are almost always better off NOT to switch to earlier hybrids with less yield potential.  Hybrids of the same “heat unit maturity” will also vary in relative flowering dates, sometimes by several days.  They can also vary in drydown rate (and staygreen, which affects drying rate). 

So, taken together, what does this mean?  In general, I can’t recommend switching hybrids from your “normal” full season choices until, AT LEAST, May 20th. While that will be later than the optimum planting date—you will sacrifice some yield, switching to earlier (and probably lower yield potential)  hybrids isn’t likely to make you money.   With some, relatively, earlier-flowering hybrids, that date is probably May 25th or after.  One person asked me, “What about drydown problems, like we saw in 2009?” Those problems were largely the result of a cool July and cold August, REALLY RARE OCCURANCES!  Even with some drying issues, full season hybrids consistently gave the highest yields and net profits.

It is already mid April and you’re ready to plant corn!  Why is soil temperature so important?  We all know that soil temperature should be hovering in the 50 degree area for corn to germinate but what many do not know is that it takes two things in the right amounts to properly start the corn seed germination process.  One is the right temperature and secondly, the seed needs to absorb around 30% of the seeds weight in water to begin the process in cooperation with soil temperature.  (Note: soybeans need to absorb about 50% of the seed weight.) 

Please consider this!  Many of the near term weather forecasts I have heard are saying cooler temperatures and some form of moisture which potentially may not allow near term soil temperatures to rise or stay like we hope it should.  We have all heard of seed lying in the ground for up to three weeks before it emerges hence we may reason that with the help of today’s seed treatments the seed still germinates and produces corn … so what can happen? 

Keeping in mind it takes the right (1) temperature and (2) amount of water to start germination, problems can arise in cool soil conditions!  Even though the temperature is not adequate to start germination the seed still continues to absorb water through the germ area of the seed. The amount of water absorbed will go above and beyond 30% of the seeds weight to the point where the seed expands so much that it breaks the clear pericarp layer surrounding the seed.  The longer seed lays in cool ground with its pericarp broken is like opening the barn doors wider to allow soil / disease pathogens unlimited opportunity to enter the seed.  These pathogens may increase the possibility of seedling damping off and or surviving plants will be at a greater risk of disease infection that may show up later in the year in the form of fungal diseases like stalk rot or bacterial problems or weaker, susceptible yield robbed plants.      

Consider that we still have a lot of time to plant for the best yield potential.   

As planting season rapidly approaches, I was trying to think of a cutting-edge agronomy topic to blog about. However, after some thought I have decided to hit on some pretty basic, yet extremely important, topics regarding crop stand and establishment. A typical bag of seed today is loaded with “technology” but it cannot be unleashed without some good old fashioned sound agronomic practices. Once corn and soybean crops approach canopy early in the summer, the vast majority of their yield performance is out of our control. There are a few inputs such as foliar fungicides and insecticides which we still have at our disposal if the situation warrants, but for the most part we are at the mercy of Mother Nature in terms of temperature, rainfall, and sunlight intensity which are key factors for yield. Prior to that however, there are several things that are very much in our control. Rapid establishment of a uniform crop is of utmost importance if we want to even have a shot at approaching full yield potential at the end of the year. The following are a few key points to consider as planting time nears:

1. Proper Planting Depth – As simple as it may sound, shallow planting depth with corn can lead to many significant problems. When seed is planted too shallow, fewer root nodes are able to establish beneath the soil which leads to a restricted and overall lesser root mass. Plants may emerge uneven, lodge later in the year, be more prone to nutrient deficiency symptoms early in the year, have reduced water uptake under drought, and be more prone to rootless corn syndrome if soils are dry early in the year. Anything less than 2 inches is typically not ideal for most soils.

2.  Compaction – Anything that limits root development will usually limit yield. Stay out of fields when they are wet. An extra 24-48 hours can make a big difference in regards to side-wall compaction. Avoid excessive down pressure unless needed to ensure proper planting depth. Spike toothed closing wheels have been shown to help avoid side-wall compaction in damp soils by enabling fracturing of the side-wall. However, the best practice is too simply stay out of fields when questionable.
 

3. Seed Spacing – Most planters are quite capable of accurately planting a wide range of seed sizes if utilizing the correct plates and air pressure. For finger units make sure backing plates are not worn and fingers are all working properly. Unfortunately it is impossible to “manufacture” seed size equally across many different hybrids and varieties. Excessive planter speed works against you. One study I saw showed a 24 bushel decrease in yield when planter speed was increased from 4.5 mph to 7 mph. Across 1,500 acres of corn that is…………….well a lot of $$$$$$$.

4. Early Season Weeds – Start with a clean field if at all possible. Both corn and beans (especially corn) are sensitive to early season weed competition even at low to moderate pressures if the weeds emerge ahead of or at the same time as the crop. Post applications of glyphosate have enabled many of us to clean up messes but in many of these cases significant bushels have already been lost. Most corn acres utilize a pre-emergence herbicide but many soybean growers still rely too heavily on post emerge only. Consider using a pre-emergence herbicide ahead of soybeans at least on a percentage of your acres. Holding back grass and small seeded broadleaves including marestail, waterhemp, and lambsquarter is often very beneficial.
 

5. Crop Residue – Excessive surface residue can present challenges ranging from poor seed to soil contact to nutrient immobilization. If applicable, set row cleaners low enough to move most residue out of the row zone to ensure hair-pinning does not occur and good seed to soil contact is established. However, avoid setting them too deep. Moving a lot of soil is undesirable, as it creates a place for water to accumulate or wash on sloping fields. Fields with excessive surface crop residues may be more prone to nitrogen immobilization if your sole primary source of N is broadcast surface applied.
 

* Any portion of yield potential lost early in the season is gone for good with little chance of recovery in full no matter how favorable the growing season is later in the year. The five topics discussed here can go a long way toward ensuring that our crop(s) get off to a good start and maintain optimum yield potential.   If you have questions, contact your local Hoegemeyer agronomist, district sales manager or dealer.