An Investigation of the Effects of Seasonal Changes, Leaf Maturity, Nitrogen Deficiency and Leafhopper Injury on the Chlorophyll Content and Diffuse Reflectance Spectroscopic Properties of Orchard Leaves

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Abstract
Diffuse reflectance spectroscopy was used to measure leaf surface reflectance and pigmentation to reveal any changes caused by seasonal variation, leaf maturation, nitrogen deficiency and feeding leafhoppers. Leaves were also analyzed for chlorophyll content. Significant changes in yellow-to-green leaf pigment ratios were observed between May and June readings for Red Delicious and McIntosh varieties' and also between the July and August readings for Red Delicious. Significant differences were also noted for measurements of chlorophyll content and leaf surface reflectance for the two apple varieties between May and June observations. Leaves from apple trees infested with leafhoppers showed significant changes in pigment ratios and diffuse reflectance from controls and differed from results previously reported for damage caused by mite infestation. Nitrogen deficiency produced the greatest changes in chlorophyll content, reflectance and pigment measurements.