Flooded Fields: Have I Lost All My Nitrogen?
In many parts of northern Indiana and Illinois, the practice of applying anhydrous ammonia (AA) with N-Serve™ to stabilize the nitrogen is quite common. Nitrogen prices are generally less expensive in the fall and diverting some of the spring field work to the fall helps if labor and machinery are limited. These are common reasons given for fall nitrogen applications. However, applying nitrogen in the fall can be risky as the nitrogen is vulnerable to loss.
Here’s a quick review of what happens to AA when applied in the fall: The AA converts to ammonium (NH4) in the soil. Ammonium is positively charged and is held tightly to the negatively-charged soil. If soil temperatures are warm (above 50ºF) the soil microorganisms quickly convert ammonium to nitrate (NO3). Nitrate is then subject to loss through both leaching, since it is negatively-charged, and denitrification (converted to N2 gas in poorly-drained soils). Leaching of nitrate occurs more often in sandy soils with low CEC. Nitrogen stabilizers such as N-Serve slows the conversion from ammonium to nitrate, thus prolonging the nitrogen in the soil until it can be utilized by the crop. The colder the soil temperature, the slower the conversion to nitrate and the less potential for loss. This is why AA plus N-Serve applications should be made after the soil temperatures drop below 50ºF and closer to the time when the soil freezes.
Fortunately, N-Serve is bound tightly to the soil and does not move even in flooded conditions. Ammonium is also held tightly and should still be in the rootzone of soils with CEC’s greater than 5. In soils with CEC’s less than 5, movement of ammonium may occur. Coarse-textured soils with low CEC’s should not be considered for fall applications of nitrogen.
An advantage we have is that the flooding occurred during the winter months when soil temperatures were low and the risk of nitrate loss is minimal. However, if flooding occurs during the spring when soil temperatures are higher, then the nitrogen losses are greater both through leaching and denitrification. Monitor your corn crop next spring for signs of nitrogen deficiency and develop a plan to address those fields with side-dress or high clearance applications of nitrogen.
Have a great rest of the week!
Dan Childs, Agronomist
