Dr. Dan Talks Agronomy

The 2015 corn crop is a mixed bag; while the year is far from over, August is a good time to pause and think if there's anything to be learned from this crazy season.

Let me start by admitting that I've been blessed. Our family farm in northeast Nebraska has had abundant rain, but not excess. We were wet in late May, June and the first three weeks of July, receiving a couple inches of rain a week. However, we were spared those 4- or 5-inch events that hammered parts of the central Corn Belt. Our corn and soybeans look like an Illinois crop in a normal year, and we are well on our way to a bumper crop -- although we could use some rain now that the corn is pollinating.

Other growing regions are not so lucky. Tales of flooding, delayed planting, prevented planting, lost nitrogen and other issues vary widely.

I see three main things to talk about at this point in the season: loss of nitrogen; reduction in stand/stress on ear development; and possible delays in development and late harvest due to wet and cloudy weather.

NITROGEN LOSSES

There are acres and acres of yellow, nitrogen-stressed corn. My rule of thumb: You need 100 pounds of nitrogen available in the top 2 feet of soil, measured via a pre-sidedress nitrate test, to make a crop. This year the rains gave us few rescue options as nitrogen levels dropped and it was either too muddy or the corn grew too tall to sidedress.

Rescue strategies generally involve applying at least 50 pounds of N per acre as soon as possible -- either with a plane or a high-clearance sprayer with a front-mounted toolbar that can dribble or disk in liquid nitrogen. Before making a rescue investment, it's important to assess the corn stand and the economic viability of the crop.

In many cases, we're not visually seeing evidence of depleted nitrogen until tassel with premature firing of lower leaves. There is less likelihood that corrections can be successfully made after pollination. It takes rain to move nitrogen into the soil profile for root uptake, and this is a time when root activity is starting to decline. In some cases, flying on 2 or 3 few gallons per acre of a urea-formaldehyde 28% liquid (5 to 8 pounds) with a fungicide could provide enough of a rescue to get the crop through grain fill if lower leaves are firing prematurely.

EAR DENSITY AND SIZE

Corn yield is decided by plants per acre, ears per acre, ear size and kernel weight. With this year's rains and saturated soils, seedling stress and disease took a toll. Plants stunted by yellowing due to saturated soils or nitrogen deficiency or with poor root systems may lack ears or have smaller ears with fewer rows around or potential kernels per row and yield potential is reduced. This is the year to do a yield check in August to see if ear count and size meet your expectations, even if the crop appears green and lush.

RACE TO MATURITY

Everyone wants corn to reach maturity before the frost and dry down as much as possible before harvest. Early cool and cloudy weather and rain has been punctuated by periods of heat and humidity, and that's helped the crop. However, in many areas, the excessive rain has also resulted in variable field and crop conditions. An article by Robert Nielsen, Purdue University agronomist, is well worth a read. Among the points he makes is an observation that ear shoot development from stunted, waterlogged plants was slower than earlier and healthier plants from the same field. He concluded that silking could be delayed by a week in those damaged plants. See that article here: https://www.agry.purdue.edu/….

Should we have more cloudy and rainy weather this summer, crop maturity could be a problem. With that comes the need to evaluate fields for molds. Scheduling fields to be harvested becomes more critical, and we'll likely see the need to dry corn this fall.

Dan Davidson can be reached at AskDrDan@dtn.com

(PS/AG)

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