O. S. C. Neves, J. G. de Carvalho, F. A. D. Martins, T. R. P. de Pádua, and P. J. de Pinho, “Use of SPAD-502 in the evaluation of chlorophyll contents and nutritional status of herbaceous cotton to nitrogen, sulphur, iron and manganese”, PAB, vol. 40, no. 5, pp. 517–521, May 2005.