ABSTRACT
An experiment was conducted to test the ability of a hand held chlorophyll meter (SPAD-502 Chlorophyll Meter, Minolta Camera Co., Ltd., Japan) to determine cotton (Gossypium hirsutum L.) N status at sites in Alabama and Missouri. Nitrogen was applied at rates of 0, 45, 90, 135, 180 and 225 kg ha-1 to establish a range of cotton N status. Chlorophyll meter readings on the uppermost fully-expanded main stem leaf were compared to standard leaf blade total N and petiole NO3-N at first square, first bloom and mid-bloom as predictors of seed cotton yield. A typical curvilinear response to N fertilizer was observed in Alabama experiments. Cotton yields did not respond to N in Missouri due to adverse weather. Chlorophyll meter readings were significantly correlated to leaf blade total N at all three growth stages in all experiments. In Alabama, chlorophyll meter readings compared favorably with leaf blade total N and petiole NO3-N as a predictor of seed cotton yield at all three stages of growth. It appears that hand-held chlorophyll meters have promise as a tool to be used to determine supplemental N fertilization for cotton. However, more research will be required before chlorophyll meters can be used for routine cotton N recommendations.
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