Beninni, Elisabete R. Yonamini, et al. “Concentration and Accumulation of Macronutrients in Hydroponic and Conventional Lettuce”. Semina: Ciências Agrárias, vol. 26, no. 3, June 2005, pp. 273-82, doi:10.5433/1679-0359.2005v26n3p273.