Production of orchids is important in floriculture, and nitrogen is one of the nutrients most required by plants. However, there is little information on nitrogen leaf analysis of these orchids. We evaluated the nitrogen fertilization on leaf nutritional status and on the production of dry mass and develop a diagnostic sheet for the orchid Phalaenopsis. Five concentrations of N (0.0, 0.068, 0.136, 0.204 and 0.272 g L -1 ) in the form of ammonium nitrate, was compared for two hybrids

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... s Taisuco Swan and Phalaenopsis Pink Chiffon). The plants were grown in pots in a greenhouse. Foliar fertilization was done fortnightly during the initial 120 days, and thereafter weekly for over 120 days. From 90 days after onset of the foliar applications, leaf green index with monthly measurements up to 240 days of application was evaluated. Dry matter shoot and the N content in the first and second newly expanded leaf was determined after 240 days. Based on polynomial relationship, a higher dry mass was achieved by applying 0.10 to 0.16 g L -1 nitrogen. The second newly expanded leaf was the most appropriate plant tissue for assessing nutritional status of Phalaenopsis and foliar concentration nitrogen was optimal at 23-28 g kg -1 .