2017 Corn Planting Recommendations

Carrie Knott, Extension Agronomist-Princeton, University of Kentucky
Chad Lee, Extension Agronomist, University of Kentucky

Corn planting for much of Kentucky is quickly approaching. Given the mild winter, average soil temperatures across Kentucky for the month of March are approximately 51°F. This is similar to last year’s average soil temperature of 52°F for the same period (March 1 to 25). However, it is several degrees warmer than the 10-year average of 48°F.

There are several things to consider before planting Kentucky’s 2017 corn crop:

1. The risk of the last spring freeze ranges from April 2 to April 29 in most years (50% probability; Table 1).

Looking Ahead: Expect to See Sidewall Compaction

Chad Lee and Carrie Knott, Extension Agronomists, University of Kentucky

Figure 1. Open seed furrow is a good indicator
of sidewall compaction.

The calendar says we are getting late on planting corn. While the soil conditions are probably more important than planting date, there will be intense pressure on producers to plant corn this week. That means that some fields will likely get planted too wet. Getting into a field too soon is completely understandable given the logistics of planting multiple fields and trying to "sneak in" a field between rains.

Corn Planting Date not as Important as Other Factors

Chad Lee, Extension Agronomist, University of Kentucky
For many producers, spring planting is late. While everyone is anxious to get a crop planted, corn yield may not be as tied to planting date as we think. In fact, planting into good soil conditions may be just as important as planting date.

Fig. 1 Corn planting

Over the past few years, farmers have sent me planting dates and yields from their fields. We found that planting date has little effect on corn yield. We had 625 fields from Central Kentucky where we compared yield to planting date. The resulting curve had an r-square of 0.0823, which basically means that there is no relationship between planting date and yield in Central Kentucky (Fig. 1). When comparing planting date to yield from 59 fields in the Green River area, the r-square was only 0.1512. Again, there is very little relationship between planting date and corn yield.

Delayed Corn Planting Doesn't Mean Lower Yields

Chad Lee, Extension Agronomist, University of Kentucky

Corn planting is slower across the majority of Kentucky this year. Again, we are faced with the temptation to get into fields as soon as possible. Simply having some corn in the fields will help us sleep better at night. But if we get into the fields too early we may have nightmares later in the season. Getting into a field one day too early often leads to sidewall compaction, which can severely hurt yields.

Corn Planting and Fluctuating Temperatures

Chad Lee, Extension Agronomist, University of Kentucky

Corn planting is a little behind in 2013, but that does not mean that we will have low yields. Corn planting was behind in 2011 and 2009, but overall statewide average yields were excellent both years. Corn planting was way ahead in 2012 and overall state yields were some of the worst in recent history.

An excellent article was written about the planting date conundrum in Indiana. Here in Kentucky, we see a similar conundrum. Recently, I asked producers across the state to send me planting date and corn yield data from their operations. They sent me corn planting dates and yields from 2003 through 2012 (Figure 1). The data would indicate that the best planting dates for Kentucky would be from about the last week of April through the third week in May. Who is going to believe that?!

March Weather is a Poor Indicator of Late Spring Freeze

Chad Lee, Extension Agronomist, University of Kentucky

With all of the warm weather there have been questions about whether there is any correlation between that warm weather and the last spring freeze event. The quick answer is No!

Tom Priddy, our meteorologist ran some numbers from Paducah and Lexington on the warmest months of March over the last 100 years or so. He ranked the top 23 warmest and then identified when the final freeze event occurred. For Paducah, the average was April 12, which is four days after the median freeze date for Paducah. In Lexington, it was April 16 which is one day after the median freeze date. For those 23 warmest March months, the range on final freeze was March 22 to May 27 in Paducah and April 3 to May 4 in Lexington. In only two years out of those listed for Paducah did the last spring freeze occur in March. For Lexington, the last spring freeze always occurred later than March.

Corn Planting this Spring

Chad Lee, Extension Agronomist, University of Kentucky

Young corn plant killed by freezing temperatures. 

The weather is warm, the soil is warm, the redbuds are blooming... it seems like we should be planting corn! Some producers have sprayed their burndown herbicides, which is a good thing this season considering how large weeds could get. Some have finished applying anhydrous ammonia, which is good because soil conditions are good. Now that these major tasks are done, all that is left is to plant corn. The fields are ready, but the calendar is not.



Last season, the rains came in early and stayed late. Every farmer was pushed to get corn planted at all, let alone in a timely fashion. Late plantings, especially on soybeans did better than "early"plantings last year. The calendar says late plantings hurt yields. This spring, something internally says that everything else is ready, let's plant some corn! The fresh memory of the previous planting season says let's plant some corn! But, the calendar says not to plant corn, yet.

Check Corn Planting Depth

Chad Lee, Grain Crops Extension, University of Kentucky

As producers rush to get corn planted, please remember to take time and check planter depth from field to field. The variability in soil moisture and soil type can affect the depth that seed is placed. Ideally, most corn seed should be planted around 1.5 inches deep. Corn seed depth should not exceed 2 inches and should not be less than 1 inch. Deeper plantings will delay emergence while shallow plantings may cause lodging problems later.

Everyone is under pressure to get as much corn in the soil as quickly as possible. However, taking just a few minutes to double-check seeding depth could alleviate a lot of problems later. 

Later Corn Planting Means Faster Development

Chad Lee, Extension Agronomist, University of Kentucky

Corn planted later will germinate and emerge more quickly, and go through crop stages faster than corn planted early.  Typically, corn requires about 100 growing degree days (GDDs) to emerge and about 200 GDDs to reach the V2 growth stage. An accumulation of about 475 GDDs is required to reach V6, the stage when the growing point moves above ground.

Wet April, 2011

Chad Lee, Grain Crops Extension, University of Kentucky

Tom Priddy, with the University of Kentucky Ag Weather Center sent out the following link for April rainfall history. With six days left to report, Lexington and Frankfort both have the wettest April in history. Louisville is less than an inch from beating its record totals for rainfall. Bowling Green is fairing much better with 'only' 6.82 inches so far.

Are University Corn Planting Date Recommendations any Good?

Chad Lee, Grain Crops Extension, University of Kentucky

The recommended window to plant corn in central Kentucky is April 15 to May 15. Yet, many producers will plant earlier than this if the weather allows. Often, we hear that the first fields planted have the best yields. But, this observation is confounded, because the earliest fields planted are often well-drained and best suited for early planting. So, were the high yields due to early planting or good soils or both?

In an attempt to get at this question, data from production farms in central Kentucky were evaluated only for planting and yield. Other variables such as soil type, hybrid number, hybrid maturity, seeding rate, weed control, etc. were not considered. Each data point on each figure represents planting date and yield for a single field in a single year.  Figure 1 is the combined data for all years and the x-axis is “day of year” where 105 = April 15, 120 = May 1 and 135 = May 15. Yields in 2005 were extremely low and most planting dates were between April 10 and April 25, about the earliest planting for any of the years.

Planting corn for silage, 2011

Chad Lee, University of Kentucky

email: Chad Lee

Corn silage is a valuable feedstock for many dairy farms and some beef operations. The higher price of inputs this season puts even more pressure on maximizing yield without breaking the bank on inputs. Some of the following guidelines should help with a successful planting season and put the silage corn crop in the best position to reach high yields.

Planting corn into sod, 2011

Chad Lee and Jim Herbek, University of Kentucky
email: Chad Lee or Jim Herbek

Planting corn into sod comes with some general opportunities and challenges. Corn could generate a gross return of $500 to $700 per acre, or more, depending on yield and marketing. That is a large enough opportunity to consider taking old pasture or hay fields and converting them to corn for 2011.

While some producers have plenty of experience with corn, others are more experienced with tobacco, hay or pastures. The general comments below are targeted to both types of producers.

Corn Seeding Rates

Choosing the proper population on corn will help you maximize yields and protect your bottom line. Our old recommendation was to plant a maximum of 30,000 seeds/acre on better soils. We will increase that recommendation to about 33,000 seeds/acre for better soils. But, as our own data shows, picking the ideal seeding rate can be a bit of challenge. Available water has a huge impact on the ideal seeding rate.

In 2008, a year that was very dry, the ideal population for corn was less than 20,000 seeds/acre, well below our current recommendations. Our yields barely reached 120 bu/acre and we felt really stupid about growing corn. In 2009, a year with timely rains, the ideal population for corn was at least 45,000 seeds/acre, well above our recommendations. Our yields rose above 300 bu/acre and we felt really smart. However, the only major difference between the two years was the amount and timeliness of rain. In both years, we used the same four hybrids, the same soil type and the same fertility. (If I told you that we got 300 bu/acre of corn with 160 lbs N/acre, no one would believe me. So, I'm not going to say it.) When you "average" the two years together, yield was maximized at about 35,000 seeds/acre. Both of these years were extremes and we rarely advise farmers to make decisions based on the extremes.

Even more evidence about the influence of water on seeding rate comes from a study we conducted in 2007 at the Woodford County Farm. The rainfed corn reached a maximum yield at about 30,000 seeds/acre where the irrigated corn reached maximum yields above 40,000 seeds/acre (Figure 2). The irrigated corn received water at rates that were probably too high for most traditional sprinkler irrigation units to deliver. Five years of research on a Maury silt loam suggests that maximum yields are reached at about 30,000 to 33,000 seeds/acre (data not shown).

So, if water is not limiting, then much higher seeding rates may be suitable. However, most years in Kentucky, water is our limiting yield factor. Our soils are relatively shallow and can hold just a few inches of water at a time. Almost every year, we go through a period of two to three weeks with no water and high temperatures during seed fill. It is this period that probably does more to limit yields than most other factors each year.

As we see more and more center pivots come into Kentucky, I think we need to do some more investigation in this area. Again, the center pivots will not irrigate as well as our small-plot system. But, these center pivots can help farmers avoid extremely dry weather. If farmers have an interest in running some strips as high as 40,000 seeds/acre, I would be interested in talking with them.

For the vast majority of acres without irrigation, a maximum seeding rate of 33,000 seeds/acre on better soils does a good job of avoiding the extremes.

Figure 1. Yield response of four hybrids on a Loradale silt loam soil, Lexington, KY.

Figure 2. Seeding rate study on a Maury silt loam, Woodford County, KY, 2007.