Determination of cotton nitrogen status with a handheld chlorophyll meter

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Abstract
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.