Dr. Dan Talks Agronomy

A walk across cornfields in and around our farm reveals that stands are less than desirable this year. Gaps and uneven emergence are a severe disappointment, especially when there's so much invested in precision equipment to get those stands right. The soil appeared to be in good physical condition this spring, so what happened?

The problems I've seen are mostly in no-till fields and particularly in no-till corn following corn. However, I've also seen some problems in corn after soybeans. I've even seen some less-than-perfect stands of oats and alfalfa drilled into cornstalks using a no-till drill too.

The fact that some plants are missing and others are behind means that some bushels have already been lost.

SEEDING AND THE 4-Rs

Farmers spend a lot of time making sure they plant corn at the right depth, in the right soil conditions, at the right spacing and at the right time. Practice these four rights and supposedly you can't go wrong... right?

Obviously, you can optimize the crop environment by controlling the 4-R variables. Still, weather remains the factor that can't be controlled.

A cold winter followed by a cold spring created considerable variability in soil temperatures this spring, especially under the residue that varies in depth across the field. Multiply those cold air temperatures by landscape position across the field, residue type and depth, and moisture variability near the surface.

All of these factors set us up for some extreme temperature differences in the field this spring that affected germination and emergence. To make matters worse, the air temperatures dropped to the low 40s and high 30s every morning during the first two weeks of May. The final blow was when we experienced freezing or below-freezing temperatures the third week of May. This piled more stress on corn seedlings.

Uneven emergence and plant heights are caused by variation in soil temperature and moisture, seeding depth, residue distribution and soil crusting. Non-uniform stands result in lower yields because the smaller, late-emerging plants cannot capture enough sunlight or resources compared to its taller neighbor. Unfortunately, corn isn't like soybeans that compensate for an ailing neighbor. Corn plants will not produce a larger ear because they are standing next to a blank plant.

WHAT'S NEXT?

The corn is up and growing and may appear normal from the roadside, but I'd encourage you to take a look at your fields. Measure stand count and estimate the range of corn ages by counting the number of collared leaves. A corn stalk that emerges later than its neighbor will likely be a runt and will not be very productive.

A three- to four-leaf delay can cause an 8% to 10% yield loss per plant. When adjacent plants differ by two or more leaves, the smaller plant will likely be barren.

Uneven emergence generally does not justify replanting -- especially this late in the season. Unfortunately, this is one of those seasons where tilled fields may perform better than no-till fields.

However, the 2.5 inches of rain I received last night is a good reminder that tillage is not always the answer either. Before you rush out to update your tillage equipment, remember that in springs with heavy rains, tilled fields will crust and erode more easily than no-till fields.

For more on the causes of stand variability in corn go to: http://www.agry.purdue.edu/…

Dan Davidson can be reached at AskDrDan@dtn.com

Follow Dan Davidson on Twitter @dandavidsondtn

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