| Four greenhouse experiments and two field experiments were performed in sand culture and two soils (San Antón, Cumulic Haplustoll and Fraternidad, Typic Haplustert). Tomato (Lycopersicon esculentum var. Bonanza and hyb. Asgrow EF-49) were grown at different compost and nitrogen (N) levels. An indicator leaf was chosen from which the chlorophyll concentration (ChlT), total N, and the SPAD-502 reading (SPAD) were measured. The SPAD reading was significantly correlated with the ChlT and the N concentration in all of the greenhouse experiments (I, II, III and IV). In the field experiment I there was no significant relation between the SPAD reading and the N concentration. In the field experiment II, a relation between the SPAD reading and the N concentration was observed at 28, 56, 70, 84, and 98 days after transplant (DAT). Significant relations were observed between SPAD reading and yield at 30 DAT in field experiment I and at 70, 84, and 98 DAT field experiment II. This instrument could be used to estimate the concentration of N and predict the yield of tomatoes. Presently, more information is required in order to minimize the variability of the readings. |
