Nondestructive and rapid estimation of hardwood foliar nitrogen status using the SPAD-502 chlorophyll meter

The utility of a portable chlorophyll meter (SPAD-502, Minolta Camera Co. Ltd., Japan) for rapidly and nondestructively assessing foliar N status of hardwood species was evaluated in two experiments. In experiment one (established near Raleigh, North Carolina). 0, 56, 168, or 336 kg N/ha (ammonium nitrate) was applied in June 1998 to sycamore (Platanus occidentalis L.), sweetgum (Liquidambar styraciflua L.), green ash (Fraxinus pennsylvanica Marsh.), and swamp cottonwood (Populus heterophylla L.) to obtain foliar samples with a range of N concentrations. Significant regression equations were established between foliar N concentration (obtained through chemical analysis) and SPAD value for all four species studied in August 1998. In experiment two, the SPAD meter was further tested in 1999 on sweetgum in eastern NC to examine whether crown position and the date of measurement affect the relationship between SPAD meter readings and foliar N concentrations. The slopes of the regression lines were similar but the intercepts were variable among the dates and crown positions. The best correlations between the SPAD meter readings and foliar N concentrations were obtained for the upper crown position early in the growing season and for the lower crown position late in the growing season. The SPAD meter was demonstrated to be a useful tool for nondestructively assessing foliar N status, particularly for relative comparison purposes, and may have efficient application for field assessments in decision-making and operational nutrient management programs for hardwood species. Accurate prediction of foliar % N by the SPAD meter may be difficult giving the generally medium range correlation coefficients. (C) 2003 Elsevier Science B.V. All rights reserved.