QUANTIFYING THE NONLINEARITY IN CHLOROPHYLL METER RESPONSE TO CORN LEAF NITROGEN CONCENTRATION

Chlorophyll meters have been used to provide a rapid non-destructive m ethod to estimate corn leaf nitrogen (N) concentration, although meter readings plateau at high leaf N levels. Paired chlorophyll meter and leaf N concentration data were obtained for ear level leaves at growth stages ranging from 3 wk before anthesis to 5 wk after anthesis over a 2-yr period at Ottawa, Ontario. Separate quadratic-plus-plateau mode ls best represented chlorophyll meter response to leaf N concentration for pre-anthesis, early grain-fill and late grain-fill stages; chloro phyll meter readings corresponding to the beginning of the plateau inc reased at later growth stages. Leaf N concentration was estimated well from chlorophyll meter readings up to the plateau range using growth stage specific functions (R(2) greater than or equal to 0.77) but chlo rophyll meter readings beyond the plateau should not be used to estima te leaf N concentration.