Silva, Karina Gonçalves da, et al. “Nitrogen Efficiency Indexes for Evaluating Nitrogen Uptake and Use in Ornamental bromeliad’s Root System and Tank”. Pesquisa Agropecuaria Brasileira, vol. 53, no. 6, Aug. 2018, pp. 703-9, doi:10.1590/S1678-3921.pab2018.v53.24924.