Abstract: Determination of nitrogen concentrations in tissues is an important diagnostic means for N status of plants. A pot experiment with tea plants applied with different amounts of N fertilizer was carried out to evaluate the usefulness of SPAD-502 as a diagnostic tool. The results showed that the yield of young shoots and N concentration of mature leaves responded to N application rates with a pattern of an initial linear increase before a platform was reached. There was a significantly positive linear relationship between the SPAD reading and total N concentration of mature leaves. The similar pattern of an initial linear increase followed by a platform was observed for the relationship between SPAD reading and the yield. These results suggested that the N status of tea plants may be characterized by the measurement of SPAD reading of mature leaves and the SPAD is a potentially useful rapid diagnostic tool in N fertilization recommendation. However, this needs further validation from field experiments. Those factors which may influence the precision of SPAD measurement, such as the point of test on a leaf, selection of leaves from twig (position), weather condition, in situ or in vitro analysis, surface cleaning and the number of leaves for a composite sample were also investigated.

Key words: Camellia sinensis L., chlorophyll meter, nitrogen nutrition, affecting factors, SPAD