Diagnostic tools for nitrogen management
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
The nitrogen (N) status in soils can be quite dynamic, ever changing with soil moisture and temperature conditions. As soils warm in the spring, available N is released from crop residues, animal manures or soil organic matter by microbial decomposition. Once the N is converted to the nitrate form, it is at risk of loss. This year many areas of the state have experienced heavy and persistent rains. When soils become saturated by rain, N can be lost by leaching of nitrate with the downward moving water or by denitrification, conversion of nitrate to gaseous nitrous oxide. The longer the time between when N fertilizer is applied and when the crop is actively growing, the greater the risk for N loss. Timing N application to when the crop needs it is a good management practice. “How much N is available in the soil’ and “how much N should I sidedress” are two common questions asked by farmers. Coming up with a reasonable answer can be challenging given variable weather conditions. A soil N test can provide information about the available N status of the soil.
For vegetable crops, collect soil cores to a depth of 12 inches, mix the soil thoroughly and dry as quickly as possible before sending the soil to the testing lab. The test result will indicate how much N is available and will provide a guide for how much additional N, if any, is needed.