Monitoring Crops for Nitrogen Deficiency

Nitrogen deficiency is fairly easy to diagnose because of the unique symptoms expressed in plants: initial lower leaf yellowing with the leaf tip and mid-rib affected first. However, by the time such deficiency symptoms become evident, yield reduction may have occurred, depending on the growth stage. The chlorophyll meter is a relatively new tool for nitrogen management which can detect developing nitrogen deficiencies before they are visible, and before they can significantly reduce yield. Current UNL recommendations for the use of the chlorophyll meter for corn suggest the application of 20-40 lb. nitrogen per acre if meter readings from the field are more than 5 percent below readings from adequately fertilized reference strips. Other recent methods for detecting nitrogen stress are the lower stalk nitrate test (which indicates after the season if the nitrogen supply to the crop has been adequate or limiting), and remote sensing imaging (which can detect developing nitrogen stress similar to the chlorophyll meter). The producer may be able to use a chlorophyll meter or remote sensing to detect nitrogen stress in time to correct a deficiency during a growing season, either with high clearance applicators or via fertigation through center pivot irrigation systems.