Corn, Wet Soils, Delayed Sidedressing, and Crop Effects

Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu

Many corn fields are too wet to go across and recent rains have caused more delays to corn sidedressing. Corn is getting too tall for tractor drawn sidedressing equipment in many cases and high clearance applicators will be needed. Thousands of acres have stunted growth due to excessive water and many low areas are drowned out. The following are some answers to critical questions about corn in this wet season.

If I delay sidedress N application too long will there be a yield loss?
Research has shown that corn that is sidedressed late may have little yield loss. In a study by the University of Missouri, researchers evaluated the yield impact of delaying N applications until the late vegetative growth stages and as far as silking. They conducted 28 experiments with timing of a single N application as the experimental treatment. This was their results: “We found little or no evidence of irreversible yield loss when N applications were delayed as late as stage V11 (11 leaf stage), even when N stress was highly visible. There was weak evidence of minor yield loss (about 3%) when N applications were delayed until stage V12 to V16 (12 to 16 leaf stage). Only 3 of the 28 experiments had N applications later than V16-all were at silking and relative yields were 71%, 89%, and 95%. Though full yield was not achieved when N applications were delayed until silking, yield was still highly responsive to N application at this stage” [Corn Yield Response to Nitrogen Fertilizer Timing and Deficiency Level" by Peter C. Scharf, William J. Wiebold and John A. Lory, Dep. of Agronomy, 210 Waters Hall, Univ. of Missouri, Columbia, MO 65211 in the Agronomy Journal 94:435-441 (2002)].

How much nitrogen has been lost in wet soils?
The combination of leaching and denitrification losses in wet soils can be over 60%. Sidedress applications should be adjusted upward accordingly.

Corn appears to be going backward in some fields. Why?
In wet soils, root growth has slowed because of the lack of oxygen. When roots are not functioning, nutrient uptake will be limited and top growth will be affected. There will also be severe nutrient deficiencies as roots cannot supply essential mineral nutrients to support top growth. Some roots may have died due to lack of oxygen or to root diseases. In addition, considerable nitrogen has been lost in soils due to leaching and denitrification, so even if growth resumes in drier weather, there will not be enough nitrogen to support top growth.

Why does later planted corn and replanted corn seem to be impacted more than earlier corn?
Late planted corn has a much smaller root system and again that root system is not functioning well in wet soils so effects are magnified. Earlier planted corn established a larger root system before soils became overly wet. These roots serve as a storage area and can supply the plant with some nutrients when conditions are suboptimal. Replanted areas are normally in the wettest parts of fields and therefore you would expect them to perform poorly in a wet year.

Will corn in low areas and wet fields recover?
Recovery will depend on 2 factors – air getting to the roots and adequate nitrogen being applied by the time of silking. If soils stay wet, roots cannot get enough oxygen and no amount of fertilizer will help. If nitrogen is not applied, also expect poor performance. In addition, some roots have already died due to lack of oxygen, some roots have been infected by disease organisms, and some root rots have already become established. If diseases have started to attack roots, expect poor corn performance even with drier weather.

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