RELATIONSHIP BETWEEN CHLOROPHYLL METER READINGS AND TOTAL N IN FALL PANICUM LEAVES (Panicum miliaceum L.) AS AFFECTED BY NITROGEN TOPDRESSING

A portable chlorophyll-content meter for proportional estimate determinations (SPAD-502 indices) allows instant readings, and may be ideal to predict N requirements, since the method used in the laboratory is time-consuming and destructive. Consequently, this work’s objective was to evaluate the relationship between chlorophyll meter readings and total N contents in leaves of fall panicum plants, at the stage prior to flowering, as affected by topdressing N levels. The experiment was installed in asbestos cement boxes (50 L), under a plastic tunnel, at Faculdade de Ciências Agronômicas/ UNESP - Botucatu (SP), using a randomized block experimental design organized as a 2×6 factorial arrangement, in which treatments consisted of 2 fall panicum cultivars (AL Mogi and AL Tibagi) and 6 nitrogen fertilization levels (0, 40, 80, 120, 160, and 200 mg L-1). The SPAD index values (chlorophyll) in leaves, as measured with the chlorophyll meter, and total N content variables were analyzed. The data were submitted to analysis of variance, means comparison, polynomial regression, and simple linear correlation analyses. The cultivars showed similar behavior for the evaluated variables, as a function of N topdressing fertilization. The application of 40 mg L-1 N on fall panicum was sufficient to increase SPAD index and N content values. The SPAD and N content values in the leaves were positively correlated. This means that the chlorophyll meter can be used to indicate potential N deficiency in fall panicum