Porntip Kaewkong and Sayan Sdoodee

pp. 731 - 741

Abstract

A chlorophyll meter (SPAD-502) was used to assess nitrogen status and total chlorophyll in longkong
leaves, leaves from twelve of 10-year-old trees grown in the experimental plot at Prince of Songkla University, Songkhla province. The relationship between SPAD-502 meter reading and nitrogen status and total
chlorophyll content analyzed in the laboratory was evaluated during 8 months (May-December 2003). It was
found that the trend of the relationships in each month was similar. There was no significant difference
among regression linears of all months. The data of 8 months showed that SPAD-reading and nitrogen
content, and SPAD-reading and total chlorophyll content were related in a positive manner. They were Y =
0.19X+10.10, r = 0.76** (n = 240), and Y = 0.43X-7.89, r = 0.79** (n = 400), respectively. The SPAD-502 was
then used to assess total nitrogen and total chlorophyll content during imposed water stress. Fifteen 4-yearold plants were grown in pots (each pot containing 50 kg soil volume). The experiment was arranged in a
completely randomized design with 3 treatments: (1) daily watering (2) once watering on day 7 (3) no watering with 5 replications during 14 days of the experimental period. Measurements showed a continuous
decrease of SPAD-reading in the treatment of no watering. On day 14, a significant difference of SPAD reading values between the treatment of daily watering and no watering was found. Then, the values of
nitrogen content and total chlorophyll were assessed by using the linear regression equations. From the
result, it is suggested that the measurement by chlorophyll meter is a rapid technique for the evaluation of
total chlorophyll and nitrogen status in longkong leaves during water stress.