FIELD CHLOROPHYLL MEASUREMENTS FOR EVALUATION OF CORN NITROGEN STATUS

An experiment was conducted on Norfolk sandy loam soil (Fine-loamy, siliceous, thermic Typic Kandiudults) during two years to determine the feasibility of using field chlorophyll measurements for evaluation of corn (Zea mays L.) N status. Nitrogen was applied at rates of 56, 112, 168, 224, 280 and 336 kg ha-1 to establish a range of corn chlorophyll levels, tissue N concentrations, and grain yields. At the V10 and midsilk stages of growth, field chlorophyll measurements were taken with a hand-held chlorophyll meter (SPAD-502 Chlorophyll Meter, Minolta Camera Co., Ltd., Japan)3 and tissue N was determined. A typical curvilinear grain yield response to N fertilizer was observed both years; maximum agronomic yields were obtained with 227 and 242 kg N ha-1, respectively, in 1990 and 1991. Tissue N concentrations at V10 and midsilk were a good predictor of grain yield. Field chlorophyll measurements were highly correlated with tissue N concentrations at both growth stages during both years of the study. Field chlorophyll measurements had excellent grain yield prediction capabilities, even at V10, which shows promise for utilization of this tool for in-season N recommendations. However, further calibration of field chlorophyll measurements will be required prior to routine use for corn N recommendation purposes.