“…There is wide variation in the chemical composition of plant species (Meda et al, 2002a, Lima, 2004 for water-soluble Ca, Mg and K. In peanut the contents of these elements were higher than in oat (Table 4). This high content of H and Al + can be neutralized by plant residues of peanut, since the Ca, Mg, K, Mn, Zn, Cu, and Fe cations bound in organic compounds are replaced by H or Al 3+ , forming stable protonated compounds or Al-organic complexes .…”