Two experiments were conducted to determine the application of rapid nitrate test in detecting changes in N and NO3–N concentration in pineapple [Ananas comosus (L.) Merr.]. The experiments aimed at determining the sampling protocols, and establishing the critical sap NO3–N levels from the relationship of foliar sap NO3–N and vegetative yield. Rapid NO3 test using Merkoquant® nitrate test strip was used. Sap NO3–N including tissue NO3–N and total N increased with levels of N fertilization. Among the leaf types, D-leaf had highest sap NO3–N level. The achloprophyllous leaf section consistently had higher NO3–N concentration (164.53 to 320.8 ppm) than the chlorophyllous section (7.72 to 13.77 ppm.) Sap NO3–N generally increased towards the afternoon with highest in 1400 to 1600 hour. Increasing the level of fertilizer from 0 to 16 g N/plant increased sap NO3–N, oven dry tissue NO3–N and total N. Sap NO3 –N was strongly correlated with total N (r = 0.82) and dry NO3–N (r = 0.91). Sap NO3–N was also significantly correlated with number and length of leaves, plant size, stem, leaf and plant dry weight. Tentative critical sap NO3-N ranged from 397.33 to 418.21 ppm and dry tissue NO3-N from 2,282.76 to 2,490.96 ppm. Further studies to establish critical sap NO3–N value from its relationship with harvestable yield and to validate whether or not it can accurately predict N needs have to be pursued.

Key words: Merkoquant® test, sap nitrate test, quick test for pineapple, nitrogen diagnosis, pineapple, Ananas comosus