The water-soluble organic compounds of plant residues released on the soil surface can improve the subsoil fertility, due to the neutralization of acidity and Ca and Mg transport. An experiment was conducted at the Instituto Agronomico do Parana (IAPAR), Londrina, to evaluate the effect of water-soluble organic compounds of plant extracts on the chemical characteristics of a dark Red Latosol (Typic Haplortox), on soil samples in columns. The treatments consisted of: distilled water, lime incorporated in the 0-5 cm soil layer, lime and percolation of the following plant extracts: oilseed radish, black oat and wheat, maize and soybean straw. The following properties were determined in the plant extracts: the water-soluble organic ligand (WSOL) by potentiometry with selective Cu2+ electrode; titration of organic anions (TOA) and organic anions (OA) by base addition. The OA and TOA concentrations varied from 7.0 to 32.0 mmol L-1 and WSOL from 0.60 to 2.23 mmol L-1. All plant extracts increased pH and exchangeable Ca, Mg and K and decreased the potential acidity and exchangeable Al down to a soil depth of 15 cm, while the effect of lime without plant extract was only observed down to 10 cm. The soluble organic compound concentrations of the plant residues were correlated with pH, Al3+, H+Al and soil base saturation in the 0-20 cm layer, confirming the role of these organic compounds to improve the chemical characteristics of an acid soil as well as the action of the surface-applied lime.
lime; organic ligand; soil acidity; basic cations; green manure
