Estimating Leaf Nitrogen of Eastern Cottonwood Trees with a Chlorophyll MeterThis article is part of a larger document. View the larger document here.
The utility of the SPAD-502 chlorophyll meter for nondestructive and rapid field determination of leaf nitrogen (N) has been demonstrated in agricultural crops, but this technology has not yet been extended to woody crop applications. Upper canopy leaves from a 5-year-old plantation of two eastern cottonwood (Populus deltoides Bartr. ex Marsh.) clones established on a former agricultural field were collected to determine the relationship between SPAD values and foliar N. The two clones, Stoneville-66 and Stoneville-75, differed in chlorophyll concentrations but had similar leaf N concentrations; relationships between N, chlorophyll, and SPAD values were not influenced by clone. Total chlorophyll was closely associated with total N concentration (mass basis) and content (area basis) (r2 = 0.76 and 0.66, respectively), and SPAD values accurately predicted total N concentration and content (r2 = 0.74 and 0.67, respectively). Results from this study indicate that SPAD-502 values < 32 signify a N deficiency level severe enough to limit the productivity of eastern cottonwood. The SPAD-502 chlorophyll meter shows promise as a tool for rapid field estimation of leaf N concentration or content in eastern cottonwood trees. Our findings support the development of this technology for use in eastern cottonwood or other short-rotation woody crop applications. Future investigations should be expanded to examine other eastern cottonwood clones on other site types and to standardize sampling protocols for various stages of tree phenology.