Estimation of leaf nitrogen concentrations in Quercus robur L. using the CCM-200 portable chlorophyll meter for different patterns of vegetative growth and acorn production

Abstract

The potential of the CCM-200 chlorophyll meter for providing accurate estimates of total nitrogen concentrations was studied from 2009 to 2011 using pedunculate oak (Quercus robur L.) leaves collected in a field trial near Zagreb, Croatia. A fertilization treatment carried out in early spring 2009 and in variable weather conditions caused between-year differences in acorn yield and production of second and third flush shoots. A total of 10 linear calibration equations were constructed based on data from leaves sampled in early July (first flush leaves), in mid-August (second flush leaves) and in mid-September (first and second flush leaves). These equations reliably described (p < 0.001) the relationships between chlorophyll content index values (CCI) measured by the chlorophyll meter and leaf nitrogen concentration (LNC) with respect to the year and month of sampling. The results suggest that variable seasonal dynamics of LNC are influenced by second and/or third flushes as well as by acorn yield. This finding has negative consequences for applying the chlorophyll meter as a suitable tool for LNC assessments during a growing season or over several growing seasons. However, the chlorophyll meter still proved to be a potentially useful tool for LNC estimations, but only when calibration equations were constructed based on the first flush leaves sampled in mid-September (in the last third of a growing season).