DETERMINATION OF COTTON NITROGEN STATUS WITH A HAND-HELD CHLOROPHYLL METER

The ability of a hand-held chlorophyll meter (SPAD-502 Chlorophyll Meter3, Minolta Camera Co., Ltd., Japan) to determine the N status of cotton (Gossypium hirsutum L.) was studied at field sites in Alabama and Missouri. Meter readings on the uppermost fully-expanded leaf were compared to leaf-blade N and petiole NO3-N at first square, first bloom and midbloom as to their seed cotton yield predictive capability. Nitrogen was applied at rates of 0, 45, 90, 135, 180 and 225 kg ha-1 to establish a range of cotton chlorophyll levels, tissue N concentrations, and seed cotton yields. A typical curvilinear cotton yield response to N fertilizer was observed in Alabama experiments. Because of adverse weather conditions, cotton yield in Missouri experiments did not respond to N. Chlorophyll meter readings were significantly correlated to leaf-blade N concentration at all three stages of growth for all experiments. In Alabama, chlorophyll meter readings compared favorably to leaf-blade N and petiole NO3-N with respect to their seed cotton yield predictive capability at all three stages of growth. It appears that hand-held chlorophyll meters would be as reliable as leaf-blade N and petiole NO3-N for predicting supplemental N fertilization requirements of cotton. However, more research will be required prior to use of chlorophyll meter readings for routine cotton-N recommendation purposes.