Tree leaf reflectance: a promising technique to rapidly determine nitrogen and chlorophyll content

Eight-month-old loblolly pine (Pinustaeda L.) seedlings were grown in a greenhouse nutrient sand culture for 110 days. Eight levels of nitrogen (1, 5, 10, 25, 50, 100, 250, and 400 ppm) were added to the nutrient solution. The effect of nitrogen level on growth and relationships between needle reflectance in the visible region and needle nitrogen and chlorophyll contents were determined. Maximum growth occurred with the 100-ppm nitrogen treatment. Needle nitrogen content was negatively correlated with needle reflectance. Nitrogen content of loblolly pine needles could be rapidly and accurately estimated from needle-reflectance measurements when all other elements were held at sufficient levels. The results suggest that reflectance measurements can also be used to detect changes or relative differences in chlorophyll content.