Portable chlorophyll meter can estimate the nitrogen sufficiency index and levels of topdressing nitrogen in common bean

ABSTRACT The nitrogen sufficiency index (NSI) obtained by using a portable chlorophyll meter is a practical alternative to evaluate the N levels in plants. This study aimed at determining the appropriate NSI value for leaves of common bean plants, in order to define the need and amount of N to be applied as topdressing, using the Minolta SPAD-502 portable chlorophyll meter. Three field experiments were conducted using a randomized blocks design, with four replications. Nitrogen doses were applied as topdressing and compared with a treatment in which a high dose of N was used as a reference to calculate the NSI, whose value was 95 %. According to the results observed using the chlorophyll meter and the NSI, for each 0.1 percentage point increase in the NSI to reach the adequate level (95 %), it is necessary to apply 1.1-1.5 kg ha-1 of topdressing N.