Dynamic of ions in acid soil leached with green manure residues extracts and pure solutions of organic acids

Abstract

The influence of green manure residues addition in the dynamic of ions in acid soils is not well known. In this study, ion mobility in a sample of the Bw horizon of an Dark-Red Latosol (Oxisol), leached with citric and succinic acid pure solutions and with aqueous residue extracts of black oats (Avena strigosa) and oil seed radish (Raphanus sativus) were evaluated in soil columns (5, 10, 20, and 40 cm long by 4 cm diameter). After the solutions and extracts passed through the soil columns, the following parameters were determined: solubles contents of Ca_s, Mg_s, K_s, Al_st (total), Al_so (organic), Al_sm (monomeric) and dissolved organic carbon. In soil, the parameters evaluated were the exchangeable contents of Ca_ex, Mg_ex, K_ex, and Al_ex and pH (CaCl₂). Citric and succinic acids increased Al_st and Ca_s contents, respectively, resulting in decreasing exchangeable fractions of these elements in soil. Black oats extract was more effective to extract Ca_ex and oil seed radish to extract Al_ex. The decrease in Ca_ex and Al_ex was followed by an increase in K_ex. Organic complexes formed with low molecular organic ligands and Ca_s and Al_ex were suggested to play a role in the mobility of ions in subsoils of acid soils after the addition of both crop residues extracts and pure organic acid solutions.