Itching to plant corn?

Hindsight is usually good, but often embarrassing. We’re all good at hindsight; it is 20:20. On the other hand, experience guides the best foresight — unless one has prophetic tendencies. One gifted in foresight chooses a wise and sensible course of action.

You may wonder how this relates to corn. I’ll address here impacts of weather on yield responses to corn planting dates, keeping in mind, hindsight, foresight and, something not mentioned yet, insight.

Hindsight. The August Farmers’ Almanac headline sounded threatening, “Get ready for, a wet, wild winter, 2012.” But now after we’ve suffered little of that, it sounds a bit ridiculous! In fact, most would suggest we had a dry and mild winter. A national map associated with the article displayed winter outlooks for the lower half of Iowa: average temperatures and very wet. And for the upper half of Iowa: very cold with average snowfall.

Even the best miss the target occasionally. The official October 2011-12 Winter Outlook from the National Oceanic and Atmospheric Administration called for a greater chance of below-normal temperatures across much of the state with the best chance in northern Iowa. For precipitation, they forecasted a greater chance for above-normal precipitation around the northern and eastern edges of the state. There were equal chances for above, normal or below-normal precipitation for the remainder of the state.

It’s an understatement to say forecasts contradict actual conditions at times. Recent headlines from various sources tell the actual story: “New Iowa warm winter record set”; “Rewriting the record book”; and “Soil temperatures break 50 degrees F in mid-March 2012.”

We experienced June-like temperatures in mid-March! Trees budded, spring flowers bloomed, fertilizer rigs crisscrossed fields. Spring wasn’t even here, but it was “in the air”! Hindsight teaches us to be careful as we look forward, trying to predict outcomes with our current level of understanding — or confusion.

Foresight. This is a year to ignore the tales about planting corn when oak leaves reach the size of a squirrel’s ear. Warm spring temperatures may encourage early development of oak trees, as well as other native and non-native species. My advice is to wait until at least the crop insurance date in Iowa (April 11) to plant corn.

As mentioned, foresight is best guided by experience. Data (a form of experience from other scientists and Iowa planting date studies) suggests to plant corn after mid-April when soil temperatures are near 50 degrees F to maximize yield. Seed absorbs about 30% of its weight in water, and temperature does not affect that process. But temperature does affect growth of both the radicle (first root) and coleoptile (shoot). With soil temperatures below 50 degrees F, seeds readily absorb water but do not initiate root or shoot growth. This leads to seed rots and poor emergence if poor seedbed conditions are prolonged. Begin planting when soils are near 50 degrees or are quickly increasing to 50 degrees after mid-April.

Cool soil conditions early in the season increase variability in final stands. We want to give every precious seed the chance of survival unless we intend to overplant to compensate for seed viability lost before emergence. Cool soil conditions early in the season also lead to more unevenness in growth and development from one plant to another. To maximize yield, manage corn to reduce plant-to-plant variability.

Optimum Iowa corn planting dates range from mid-April to the end of April in north-central and northeast Iowa, and to the first or second week in May in other parts of Iowa (see table). If we consider the differences between early planting and late planting, yields are more stable early in the planting season than late. That means planting early during the optimum window is generally a better practice than planting a few days after the optimum window. Yields drop off dramatically in mid-May across Iowa. If possible, plant corn prior to May 15 to avoid this “slippery slope” of rapidly reducing yield potential.

Insight. Insight differs from experience-based foresight in that it embodies the concepts of discernment and emphasizes a perhaps uncommon depth of understanding. Insight is “that inner vision that sees further than the eyes,” according to W.H. Hudson (1904). Embedded within the best thinking on corn planting dates is the understanding that we should plant if soil conditions are favorable, and they are expected to remain that way for a week or so, or to improve.

For example, let’s say it is April 20 and soil temperatures are in the high 40s and rising fast. Soil conditions are excellent and you’ve got everything ready to go: The best hybrids are chosen, your planter is fine-tuned to perfection, the tractor is fueled. And the five- to seven-day forecast calls for more of the same. Would you plant? Most of us without hesitation would say, “Yes!”

Let’s change one element now: All of the factors just mentioned remain the same, but the five- to seven-day forecast is for cold, wet conditions. In fact, it might even snow! Would you plant corn? At this point, some of us may get uneasy and shake our heads gently no. Others pound tables and yell, “Of course I’d plant!” And, given their individual situations and aversion or fondness of risk, both may be correct responses. What I know is that yield will likely be compromised in the second situation due to the factors mentioned above.

Hindsight, foresight, insight?

The situation I’ve described is similar to what we experienced the second week of April 2011 and in mid-March 2012. Some farmers planted in early April 2011; most didn’t.

Once we cross the crop insurance date, April 11, if soil temperatures are in the high 40s, plant corn if soil conditions are favorable and conditions are expected that way for five to seven days, or to improve. As I think about it, this isn’t insight at all; its foresight guided by experience!

Elmore is the Iowa State University Extension corn agronomist.Visit www.agronext.iastate.edu/corn for more corn management information. For an updated Iowa soil moisture map, go to wepp.mesonet.agron.
iastate.edu/GIS/sm.phtml
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This article published in the April, 2012 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.