Chemical Modifications Caused by Liming Below the Limed Layer in a Predominantly Variable Charge Acid Soil

Abstract

Despite the low mobility in soil, surface liming has increased plant growth and yield. Since only the topsoil is affected by this technique, the benefits may be caused by improvements in soil solution. This experiment aimed to assess chemical changes in the solid phase and leached solutions after addition of calcitic limes to a Humic Hapludox. Calcium carbonate or calcium hydroxide was throughly mixed with soil samples at rates of 0, 0.25, 0.50, 1.0, and 1.50-times that required to raise soil pH to 6.0 (equivalent to 0, 3.5, 7.0, 14, and 21 t ha−1). After 60 days, treated samples were transferred to the top (30 cm) of leaching columns, filled with unlimed soil in the bottom (23 cm). Water was percolated weekly through the columns during 12 weeks. Chemical determinations were performed on all leached solutions, and at different soil depths below the limed layer at the end of the experiment. Calcium (Ca), magnesium (Mg), and aluminum (Al) increased linearly in the percolated solution with increases on lime sources; the opposite occurred for leachate pH, probably due to hydrolysis of Al that was replaced from the negative charges on unlimed soil by added calcium. Calcitic limes increased pH and Ca, and decreased Al and Mg in the solid phase below the limed layer up to a maximum of 3 cm. Lime, thus, positively affected only the top of the unlimed solid phase; its effect on leached solution, however, was similar to that caused by neutral salts on acid soils, with increases in cations and decreases in pH.