“…To make this evaluation, quantification of the chemical species considered toxic becomes necessary, mainly the labile species of Al, such as Al 3+ , Al(OH) 2+ , and Al(OH) 2 + , as well as non-toxic species, especially the complexes of Al with organic and inorganic molecules that alter the proportion and activity of the toxic forms of Al (Ferro-Vásquez et al, 2014;Hagvall et al, 2015;Nolla et al, 2015) and, furthermore, the elements that can reduce Al toxicity, such as Ca 2+ and Mg 2+ (Silva et al, 2008;Hashimoto et al, 2010;Auxtero et al, 2012). In general, Al 3+ activity, rather than measurements of the soluble or exchangeable forms, is the best indicator of toxicity potential in acid soils (Ferrufino et al, 2000;Spera et al, 2014).…”