Zotarelli, L., Cardoso, E. G., Piccinin, J. L., Urquiaga, S., Boddey, R. M., Torres, E., & Alves, B. J. R. (2003). Calibration of a Minolta SPAD-502 chlorophyll meter for evaluation of the nitrogen nutrition of maize. Pesquisa Agropecuaria Brasileira, 38(9), 1117–1122. https://doi.org/10.1590/S1678-3921.pab2003.v38.6680