Using a chlorophyll meter (SPAD-502) to estimate the total chlorophyll and nitrogen contents in leaves of 'Manee-Esan' pummelo

The chlorophyll meter (SPAD-502) is a simple tool which can expediently estimate the total chlorophyll and nitrogen contents in many species. However, the relationship between the total chlorophyll and leave nitrogen contents, with the SPAD readings in 'Manee-Esan' pummelo (Citrus grandis (L.) Osbeck), have not been fully established and may be ideal to predict the nitrogen requirements. The objective of this study was to establish a correlation between the total chlorophyll contents and the possibility to estimate the leaf nitrogen status with SPAD-502 of 'Manee-Esan' pummelo. Leaves of the pummelo were sampled in May to December, 2015 and analyzed with a SPAD-502 meter under field conditions and in the laboratory to determine the degree of leaf greenness, extracted chlorophyll contents and total nitrogen contents. The results showed that the leaf greenness values, total chlorophyll contents and total nitrogen contents of the leaf samples ranged from 69.71 to 90.92 SPAD-unit, 0.57 to 1.39 mg cm(-2) and 1.40 to 2.00% N, respectively. In addition, SPAD values had a positive correlation with total chlorophyll contents and total nitrogen contents (y = 0.0311x - 1.7427, R-2=0.3473 for total chlorophyll and y = 0.0124x + 0.6809, R-2=0.052 for total nitrogen, respectively). The SPAD-502 meter readings could estimate the chlorophyll content of pummelo leaves regardless of the temporal and spatial considerations. It is suggested that the SPAD value, determined by a portable chlorophyll meter, can be used to obtain a quick estimation of the total chlorophyll and nitrogen content of the pummelo leaves.