Nitrogen management this fall
While I realize that anxiety levels rise every year when soil temperatures are not getting down to 50°F and falling steadily, I would also like remind readers that in most years, the 50°F temperature allows for N applications before soils become too wet or frozen. There is no need to increase the risk of N loss by starting applications too early. Also, applying once temperatures are 50°F does not ensure no loss of N, but it does provide a better chance to protect your investment.
Air temperatures in Illinois can vary substantially in early fall. Even if they are getting to 50°F, historically the chance that temperatures will continue to decline without a significant bounce back up are very rare before the second week of October in northern Illinois and the third week in central Illinois. On average, soil temperatures reach 50°F and continue to decrease the first week of November in central and northern Illinois. Daily maximum 4-inch bare-soil temperatures for Illinois this week have been in the mid- to upper 60s.
Up-to-date soil temperatures can be accessed at www.isws.illinois.edu/warm/soiltemp.asp. However, these values should be used as a reference. Since soil temperatures can be influenced by multiple factors (including residue cover, soil color, and drainage), it is always best to monitor soil temperatures in individual fields prior to N application.
Where can fall N be considered? Because temperatures do not stay below 50°F long enough during the winter, fall N application should not be done south of a line roughly parallel to Illinois Route 16. In areas near this boundary, soil characteristics should be evaluated to determine whether fall application is appropriate. Soils with high potential for nitrate leaching in the fall or early spring (sandy soils or those with excessive drainage) should not receive fall N applications. Also, regardless of location in the state, soils with high potential for nitrate leaching or that are very poorly drained should not receive fall N applications.
Due to the length of time before use by the crop, application of manure and other organic N sources should be done as far as possible from environmentally sensitive areas, such as on steep slopes and near bodies of water. If the application cannot be accomplished in late fall, do not apply on frozen soils in the winter; it is better to wait until spring.
How to apply N. When applying anhydrous ammonia, make sure soil conditions are fit for the application. Soils that are too dry or too wet can result in ammonia losses to the atmosphere, as the application knife tracks may not seal properly. When soils are dry, increasing depth of application or reducing application rates typically can help minimize volatilization losses. In wet soil conditions there is little that can be done to minimize such losses. If you use manure, poultry litter, or other animal-derived fertilizer, incorporate it in the soil to avoid N volatilization.