The mention of yellow, uneven corn fields in my article last week prompted several follow-up discussions and a topic for today. It is worth repeating that overall corn crop is off to a good start in Daviess County. That may not be comforting if you are one with yellow corn. Yield has been reduced in those fields, but it is impossible to predict how much.
Most yellow corn fields are due to waterlogging and subsequent lack of nutrient availability, including soil oxygen. Ultimately, too much rain is not necessarily the problem. Instead, the lack of soil drainage may be the culprit. Landowners, there have been wet springs before, but this year demonstrates the benefit of installing drain tile. If you see a dark green field with uniform growth, you can bet it has been tiled. Subsurface drainage tile systems provide excessive soil water an unrestricted flow out of the field.
This increases the depth of the root zone, reducing waterlogging and allowing roots to thrive in moist, unsaturated soil. There are other reasons why two nearby fields can be very different in color and growth uniformity. Some farms have purchased planting equipment which allows nutrients to be placed directly in the corn row or in higher concentrations immediately adjacent to the corn row. This practice does not guarantee higher yield but does provide the plant an opportunity to take up nutrient more quickly after emergence than broadcast fertility placement alone.
This quick green effect helps the plant grow and develop roots quickly. When you compare corn with planter applied fertility on tiled land next to corn on poorly drained soils waiting for roots to grow to the broadcast fertility, the color, growth, and uniformity difference will be significant in a wet spring.
Corn is resilient and while it is tempting to consider additional fertility or cultivation for yellow stunted corn, it is unnecessary. Assuming adequate nutrients have been applied, the soil simply needs oxygen to return allowing respiration to occur in the plant and green up to return.
The theory of row cultivation to increase soil oxygen is understandable, but if the wet field areas have dried out enough to allow tractor mounted cultivation to occur, then enough soil oxygen is available to restart the respiration process.
If better conditions return but corn does not green up after a week or so, there's cause for further investigation. The first step is digging some plants. If those field areas were wet at planting, sidewall compaction could be preventing root growth. To check, dig around the roots as if you were going to grow the corn plant in a flower pot. Knock the soil from the roots and look at the root structure.
Corn roots should grow in all directions from the stalk. Roots with sidewall compaction will be constricted to growth within the seed furrow. Some corn roots will show signs of sidewall compaction with other roots breaking through. This is a good thing that shows the plants have a chance.
If roots look normal, two soil tests are necessary. The first sample should be collected from the traditional 4" depth to analyze general fertility and soil water solution pH. The second sample, a soil nitrate test taken from a 12" depth, is an inexpensive measurement of available nitrogen.
If it bothers you to see these yellow, uneven fields, my advice is to not look at them for a few weeks. This article describes the outlook. It will grow but yield less than optimum. If fertility is adequate, there is no compaction restriction, and rain occurs later in the season around tasseling and ear fill, you can rest assured there will be corn to harvest and the results may surprise you. The key is to not abandon the corn. Remain on planned herbicide and fertilizer programs, but nothing more.
Focus any additional investment such as fungicide on the best fields and try to protect them for the highest yields. The most productive activity this week for poorly drained fields is to invite your landowner to visit the field and visually see its need for tile drainage.
The Daviess County Fair is scheduled for July 10-13. Fair books are available at the Extension Office or online at http://www.daviesscountyfair.com/.