EFFECTS OF LIME AND GYPSUM ON CLAY DISPERSION AND INFILTRATION IN SAMPLES OF A BRAZILIAN OXISOL

Samples of the surface layer of an acid Oxisol were treated with various amounts of CaCO3 (lime) or with CaSO4 (gypsum) and incubated in the laboratory to study possible effects on clay dispersion and infiltration. The treatments consisted of incorporation of gypsum and lime or superficial application of lime. Infiltration rates were determined with a rainfall simulator and clay dispersion by measuring clay concentration in runoff. Effects of treatments with lime or gypsum were similar in some respects but different in others. Incorporating lime increased clay dispersion and reduced infiltration rates significantly. Incorporating gypsum, in contrast, increased clay dispersion and reduced infiltration slightly as compared with the control. Highly significant correlations were found between pH and both clay dispersion and infiltration rates as well as between clay dispersion and infiltration rates. The relationship between increased clay dispersion and lower infiltration rates was linear. Application of lime to surfaces of soil samples reduced clay dispersion less than did incorporation. Covering the samples with wheat straw reduced clay dispersion and maintained high infiltration rates. On the whole, effects from additions of gypsum were more favorable than those of lime. The more favorable results suggest further tests through field trials.