SURFACE ROUGHNESS OF AN ICEPTISOL RELATED WITH SOIL TILLAGE AND COMPACTION UNDER NATURAL RAINFALL

SURFACE ROUGHNESS OF AN ICEPTISOL RELATED WITH SOIL TILLAGE AND COMPACTION UNDER NATURAL RAINFALL Surface roughness is a relevant soil property in terms of its influence on soil water infiltration and storage, sediment retention on the soil surface, and water erosion. In turn, surface roughness is influenced by soil tillage, moisture, compaction, crop residues, residual effects of land use, and by rainfall erosivity. The purpose of this study was to quantify the effect of soil tillage type, soil compaction and rainfall erosivity on surface roughness. The experiment assessed an Inceptsol with a relatively flat slope (0.03 m m(-1)) under natural rainfall in Lages, Santa Catarina, Brazil, from September to November 2008, with the following treatments: I) nearly smooth surface of compacted soil (SSC); 2) nearly smooth surface of uncompacted soil (SSNC); 3) tillage (plowing and two diskings) of compacted soil (SPC); 4) tillage (plowing and two diskings) of uncompacted soil (SPNC); 5) tillage (chiseling) of compacted soil (SCC); 6) tillage (chiseling) of uncompacted soil (SCNC). The micro-relief was determined with the contact styli of a rugosimeter six times: immediately before and immediately after treatment application; and after the occurrence of each of the following rainfall erosivity (EI30) values: 136; 190; 630; and 265 MJ mm ha(-1) h(-1). After tillage with plowing and disking and with chiseling the modified random roughness index was higher than before, in compacted and uncompacted soil. The random roughness was on average 3.72 times higher after plowing and disking and 3.88 times higher after chiseling, in compacted and uncompacted soil. The surface roughness index increased in the compacted soil, independently of the soil till type. In the case of plowing and disking, the increase was 4.58 times in the compacted and 3.04 times in uncompacted soil, immediately after tilling, while in the case of chiseling, the roughness index increased 5.49 times in the compacted and 2.61 times in the uncompacted soil, also immediately after tilling. Rainfall erosivity decreased the soil surface random roughness, independently of soil tillage and compaction; the relation was described by the model y = ae(-bx).