By Randy Simonson, Ph.D.
Technical Services Manager
The nitrogen price for farmers is at an all time high. Farmers are feeling the pressure to reduce the
amount of nitrogen they apply, however, they do not want their yields to suffer, which may cost them more money.
There are many ways to make nitrogen recommendations for a crop.
TSM® considers many variables when making nitrogen
recommendations in order to make a recommendation that is closest to the crop need as possible. TSM®
takes into consideration the crop's yield goal, previous crop, soil organic matter, and manure applied.
The previous crop is important because the residue from corn, for example, has a much higher carbon/nitrogen
ratio than soybean residue. Corn residue has a ratio of 60 to 1, which means it actually takes nitrogen to
break down the residue. Soybeans on the other hand have a carbon/nitrogen ratio of 15 to 1.
Soybean residue releases nitrogen as it is broken down. The critical factor is 25 to 1.
Residue with a carbon/nitrogen ratio greater than 25 to 1 will require more nitrogen for the microbes to
break it down. When the residue has a carbon/nitrogen ratio less than 25 to 1, plant available nitrogen is
Soil organic matter is mineralized throughout the season. This means that microbes break it down into
nutrients, which are useable by the plant. A soil with a high organic matter is going to release more nitrogen
than soils with a low organic matter. Most nitrogen recommendations do not take this into consideration,
but the TSM® program does.
Manure can provide a substantial amount of nitrogen for a crop. Approximately one half of the total
amount of nitrogen in manure is available for a crop the first year. Injecting manure or incorporating it
within 24 hours results in very little nitrogen loss to the air. However, if the manure is not incorporated, the
air nitrogen loss is up to 30%. Also, Pit-Boss can greatly reduce nitrogen losses from manure pits and
Wet weather can increase nitrogen leaching and denitrification. N-Serve reduces nitrification and the
potential for leaching and denitrification. Agrotain and sulfur coatings can reduce volatilization.
Sidedressing applies the nitrogen at a time when the crop is using it; thus there is less time for loss.
Pre-sidedress nitrate tests are used in some areas to more accurately make nitrogen recommendations.
A nitrate test also can be taken if you think you may have lost some nitrogen due to a wet spring.
Most universities contend that if you have 25 PPM nitrate nitrogen, the crop has enough nitrogen.
If the nitrate test shows less, some nitrogen needs to be applied.