ABSTRACT.
Lime requirements

Domingo Suárez F.1 y María Cristina Márquez M.1
 

Incubations with several amounts of CaCO3 (0; 1,000; 2,000; 3,000 and 4,000 mg/kg) were made with 12 Andisoland Ultisol soil sof the lX and X Region. Afier 0, 60,120 and 180 days pH(H2O)(1:2,5); pH (CaCI2) 0,01 M (1 :2,5); exchangeable Al (KCI 1 M); exchangeable Ca, Mg, Na and K (NH4-Ac at pH 7) were determined.
In addition field trials, using wheat and rapeseed as test plants, were carried out with doses of CaCO3 ranging from 0 to 4,000 kg/ha. The soil of each plot was analyzed with the same analytical determinations made in the laboratory study. These determinations were made before seedling and afier harvesting.
Correlation studies showed that the variation of the exchangeable Al, expressed as Al % Total Bases, is closertothe variations of pH measured in 0,1M CaCI2 than in H2O (r =0,91). Additions ofCaCO3 constantly increased the pH measured in CaCI2 as well as the pH in H2O. Therefore, it is possible to use the slope ofthe linear relationship as a measure ofthe soil buffer capacity (increase of pH per unit of added CaCO3).
Thus, using the found relationships it is possible to estimate the dose of CaCO3 for corrective Iiming needs using the formula:
Dose (kg CaCO3/ha) = original pH - desired pH / ∆pH/(kg CaCO3/ha)
The results ofthe field trials showed the productivity is limited when the Al%SB is greater than 20%. In those cases the corrective Iiming resulted in increase yields, being greater with the more sensible crop to aluminium toxicity.

Keywords: liming, lime rates, soil buffer capacity, aluminium toxicity, soil acidity, soil pH.
1 Departamento de Ciencias Vegetales, Facultad de Agronomia, Pontificia Universidad Católica de Chile, Casilla 306, Correo 22, Santiago. Chile.