| Summary: | Estimating photosynthetic pigments, such as chlorophylls, as well as the foliar nitrogen content is very important for the evaluation of the nutritional and physiological status of a plant. However, producers cannot easily carry out these estimations because they involve analyses in laboratories that are costly and time-consuming. The SPAD-502 total chlorophyll index meter is efficient at rapidly estimating total chlorophyll contents in situ, along with its relationship with the total nitrogen concentration in tissues. The objective of this research was to validate a non-destructive in situ method (SPAD) for use in place of destructive estimation methods for chlorophylls a, b and total, as well as the foliar nitrogen concentration in guava plants (Psidium guajaba L.), cv. Regional Roja, in three phenological stages under the conditions of the municipality of Vélez-Santander (Colombia). The data obtained with the SPAD-502 and the content of chlorophylls a, b and total were adjusted to a second-degree polynomial with correlation coefficients (r) greater than 0.91 for the three phenological stages, while the concentration of foliar nitrogen was adjusted to a linear type model with determination coefficients (R2) higher than 0.90, indicating a highly linear correlation between the non-destructive method and the destructive methods used in the present study.
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