Wet Conditions Create Weed Management Challenges in Corn

 Jim Martin and J.D. Green, Extension Weed Specialists, University of Kentucky, April 27, 2011

The prolonged wet conditions this spring have created additional challenges in regards to weed control. The following are possible scenarios that corn farmers may encounter and factors to consider as we progress through the next several days.

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.

Estimating Nitrogen Losses from Wet Soils, 2011

Lloyd Murdock, Extension Soils Specialist, University of Kentucky

Wet soils cause nitrogen losses, and determining how much nitrogen is lost is necessary to choose the proper management options.  In cases where high intensity rain results in high runoff, leaching losses will probably be low.  The primary nitrogen loss mechanism in saturated soils in Kentucky is denitrification, which occurs when soil nitrate nitrogen (NO₃-N) is converted to nitrogen gas by soil bacteria.  Two to three days of soil saturation is required for bacteria to begin the denitrification process.  Well-drained upland soils that have been wet from a series of rains probably have not experienced much denitrification.  Soils in lower landscape positions that stay saturated longer will likely lose more N.  Losses can be calculated by estimating 3 to 4 percent loss of fertilizer NO₃-N for each day of saturation.  Use the Table below to determine how much fertilizer NO₃-N was in the soil.

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.

Avoiding Sidewall Compacting During Late Corn Planting

Lloyd Murdock, Extension Soils Specialist
Plant and Soil Sciences, University of Kentucky

Sidewall compaction can result from planting a crop when the soil is a little too wet. This damaging effect can be even greater on soils with a relatively high clay content at the surface. It occurs when the double disc opener leaves the side wall of the planting furrow smooth and compacted (slick as opposed to shattered) as it pushes the soil aside. The trailing press wheel then increases the compaction with its downward force. If the soil stays very moist or wet, the roots may be able to penetrate the compacted mud at the sidewall and expand further into the soil. However, if the weather turns dry after planting, the sidewalls then harden, and roots are not able to push through since there are no pores or cracks. This causes the roots to grow within the planting furrow, along the direction of the row. Although plants may look normal at emergence, they will begin to show nutrient and drought stress after the corn is several inches high. This problem may be more common in no-tillage because no-tillage soils have better structure, and it is easier to traffic them in a wetter condition. The old adage of "waiting on no-till" is a good one. Sidewall compaction can also occur with conventional tillage. If you can mold the soil into a ball in your hand and the soil ball will not easily crumble apart, it is too wet to plant.