How much N will you lose this year?
There are at least five things to keep in mind about fertilizing corn this year, says Bruce Due, Mycogen senior agronomist, Moorhead, Minn.
We’ve been in a wet cycle.
The wet cycle will likely continue.
Anytime soils are too wet, nitrogen can be lost. In soil with poor internal drainage, you’ll lose it to denitrification. In coarse-type soils you’ll lose it to leaching.
Corn doesn’t use very much N in the first 45 days of growth. From 45-90 days, it uses a lot.
Last year, farmers who realized that they lost nitrogen early in the season and replaced some of it by sidedressing increased their corn yields.
Based on those five points alone, it will be a good idea to take a look at how to manage the risk of N loss this spring, Due says.
The level of risk mainly depends on soil type, when you apply fertilizer, and whether or not you are equipped to side-dress N.
If you have coarse soils that give up N easily, you may want to be set up to split N applications, Due says.
If you have soil that usually hangs on to N better than coarse soils, your main risk is too much rain.
You can apply N inhibitors and other products to slow losses, but it would be wise to do your homework on which products work best, Due says. It still might be a good idea to figure out how much N you can sidedress quickly and economically.
How N loss occurs
Nitrogen loss is more complicated than it first appears, according to Due.
N sources applied as ammonium (NH4+ ) are converted to nitrite (NO2- ) and then to nitrate (NO3- ) via the nitrification process.
Because soil bacteria are responsible for nitrification, rate of nitrification depends heavily on soil temperature and moisture. Nitrification typically begins when soil temperatures reach 50 degrees F. Once soil temperature exceeds 50 degrees F, nitrification rates increase with temperatures.
Under ideal conditions, the process occurs in as little as two weeks.
Because NH4+ carries a positive charge, it binds to the negatively charged soil. N losses, such as leaching and denitrification, occur when fertilizer N is converted to the negatively charged NO3- form. Fertilizer N in the NO3- form is subject to significant loss.
Leaching is caused by a negative charge. NO3- moves with water through the soil profile, and subsequently out of the root zone.
Denitrification is the microbial process of converting NO3- to gaseous forms of N due to saturated soil conditions.