Comparison of corn leaf nitrogen concentration and chlorophyll meter readings

Tissue testing of com leaves for nitrogen (N) concentration is not widely used because it is easier and perhaps more economical to apply sufficient fertilizer than to risk a yield reduction because of an N deficiency. Environmental concerns related to N fertilizer will require producers to improve N management practices to reduce the potential for nitrate leaching. Applying fertilizer N on an “As Needed” basis rather than using a “Lump Sum” approach has both environmental and economic advantages. Com leaf disk N concentrations and SPAD 502 chlorophyll meter readings from N rate studies were compared at silking for a variety of hybrids at several locations. Data indicated that chlorophyll meter readings correlated well with leaf N concentrations for a given hybrid and location. Calibration of chlorophyll meters to determine crop N status may not be practical because of the unique “greenness” characteristics of different hybrids. However, normalization procedures can be used to standardize the tissue testing approach across hybrids, locations, and growth stages. This can be achieved by comparing chlorophyll meter readings from well fertilized rows to those from the test area. Application of this technology by consultants and producers may require an adequately fertilized area of the field that can be used as a reference for local growing conditions.