Barbosa, J. G., Martinez, H. P. and Kampf, A. N. (1999) “Macronutrients content in chrysanthemum plants in hydroponic growth using expanded clay for cut flower”, Pesquisa Agropecuaria Brasileira, 34(4), pp. 593–601. doi: 10.1590/S1678-3921.pab1999.v34.5216.