Nitrogen index in leaves of tomato plants as a function of nitrogen and organic fertilization.

The N indexes constitute an important tool to evaluate the nutritional state of the plants. Consequently, the objective of this study was to evaluate the effects of N doses, with and without organic fertilization, on the N-NO3 contents in the sap and in the dry matter of petiole and total N in the dry matter of the limb of tomato plants, and to establish the critical levels in different phases of the cycle of the culture. For this and, an experiment was done in the Horta do Fundao of the UFV, in the period of November 13, 1998 to February 11, 1999. The N doses applied were 0, 110, 220, 440 and 880 kg ha-1 and the doses of organic fertilizer in the form of bovine hardened manure were 0 and 8 t ha-1, in dry base. The experiment was done in randomized blocks arranged in a 5 x 2 factorial design, with four replications. The opposite leaves were used in experiment for efflorescence 1, 3 and 5 during anthesis times. The N-NO3 from the petioles sap and dry matter; the total N contents were determined from the dry matter of the limb. The N doses increased the contents of N, with and without organic fertilization, in all the leaves sampled. These contents decreased with the development of the plants. It was concluded the indexes of N in the sap and in the dry matter of tomato plants leaves for the establishment of the nutritional status vary with the amount of applied N in the soil and the age of the plant; it was suggested the use of the concentration of N-NO3 in the sap of the petiole for the determination of the critical levels of those indexes is necessary to standardize the physiologic age of the leaves collected.