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A Southern View

Crop Observations from Southern Illinois

Nitrogen Loss Under Wet Field Conditions

Posted by Robert Bellm -

Periodic thunderstorms have rolled through the state in the past month, and continue to do so today. The spacial variability of these precipitation events serve to remind me that, while climate indicates a general trend, weather is often a very localized event. This is emphasized by the May 28 USDA Weather & Crop Report, which indicates that 89 percent of the corn crop statewide has been planted. Here at the Brownstown Agronomy Research Center we have barely been able to plant a couple of small plot areas, and those were done under less than ideal soil conditions. Claypan soils have poor surface and internal drainage characteristics, and when this is coupled with excess precipitation, standing water results. If it is any consolation, we share these challenging delays with our farming neighbors, which is why the University's off-campus crop research centers were established to begin with:  to conduct agronomic research under the various growing soils and environments found throughout the state. Our local research results are relevant to the local growers.

One question that may soon be crossing growers' minds is whether the excessive rainfall has resulted in enough nitrogen loss to justify adding additional N to corn as a sidedress application? An excellent Bulletin article by Dr. Emerson Nafziger addresses both carryover nitrogen from last summer's drought, and well as fall nitrogen applications, and how the current wet conditions may affect N losses through leaching and denitrification. Keep in mind though, that almost all of the N in southern Illinois is applied in the spring, and the cold, wet conditions this spring delayed those applications to being later normal. Nitrogen in the ammonium form is stable in the soil, and is not subject to leaching and denitrification until it has first been converted to nitrate by soil microorganisms. This conversion from ammonium to nitrate is very slow under cool and saturated soil conditions. If your spring nitrogen was applied as anhydrous ammonia, then much of it is likely still in the ammonium form and not been lost. On the other hand, if you were counting on a large amount of residual nitrogen carry over from last summer's drought, you will likely be disappointed. That residual N was already in the nitrate form last fall, and therefore much more subject to leaching and denitrification loss under this spring's wet field conditions.

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