Lime recommendation for Rio Grande do Sul (RS) and Santa Catarina (SC) States in Brazil aims to raise soil water pH up to 6.0 to most crops. For highly buffered soils containing high organic matter content, this pH value may be lower. This study was carried out to evaluate the magnitude of changes on soil parameter values related to acidity due to increases on soil water pH to 5.2, as well as to compare analytical methods for lime recommendation, and lime requirement rates to attain this pH value relatively to the actual recommendations to raise soil pH to 5.5 or 6.0. Twenty-eight soils from Santa Catarina State were limed in 1984 with increasing rates of calcium carbonate in order to get the acidity neutralization curves. After 5 months of incubation, soil pH, exchangeable Ca2++ Mg2+, K+, Na+ and Al3+, and (H + Al) were determined. From these data the sum of base (S), effective CEC, CEC at pH 7.0, percentage base saturation (V%), and Al3+ saturation on effective CEC (m%) were calculated. Four analytical methods (Al3+, H + Al, SMP, and base saturation), in addition to the sum of Al3+ and organic matter (OM), were compared to determine lime requirement to raise soil pH to 5.2. The increase of soil water pH to 5.2 decreased Al3+ from 4.24 to 0.67cmol c kg-1, H + Al from 13.04 to 8.74cmol c kg-1 and (%m) from 52 to 8%, and increased Ca + Mg from 3.61 to 8.38cmol c kg-1 and V% from 24 to 50%. All analytical methods were efficient for lime recommendation to pH 5.2, however, the combination of Al3+ and OM was the most efficient and base saturation the least efficient. To increase soil water pH to 5.2 rather than to 5.5 or 6.0 would result in an limestone economy of 1.4 and 3.0t ha-1, respectively. For the highly buffered soils, with pH-SMP equal or below 5.0, the economy would be still larger, respectively of 3.0 and 7.0t ha-1, which could attain up to 5.0 and 10.6t ha-1 for soils with pH-SMP of 4.4.
liming; pH; lime requirement methods; buffered soils
