Dynamic of organic carbon in a clayey oxisol under tillage systems

Soil organic matter is of fundamental importance to improve the structure and retention of water and nutrients. This assay aims at evaluating the dynamic of organic matter in a clayey oxisol under three tillage systems, five periods and in five depths. The experiment was conducted in the Experimental Center of Agricultural Engineering in the State University of Western Parana (UNIOESTE), in Cascavel city, Parana, Brazil, in a red latosol (usually known as oxisol) from clayey to very clayey texture (600 g kg(-1) clay; 320 g kg(-1) silt and 80 g kg(-1) sand) basalt substrate and soft-wavy relief. The area is geographically set by the coordinates 24 degrees 48' south latitude and 53 degrees 26' west longitude, 760 m average height. The treatments were composed of three soil tillage systems: CT conventional tillage = disc plowing followed by harrowing to level; RT reduced tillage = scarification without a following harrowing to level; and NT no-till farming = implantation of crops on the stubble of the previous crop. The depths of soil sample extractions, for the determination of organic carbon content, in each tillage system, were as follows: 0.0-0.025; 0.025-0.05; 0.05-0.10; 0.10-0.20 and 0.20-0.30 m. Organic carbon content was determined in accordance with the Walkley-Black methodology, from years 2006 to 2010. The experimental design used was a 5 x 3 x 5 factorial (five periods, three tillage systems and five depths). Tukey's test was applied to compare the average of treatments, with the significance level at 5%. After five years, NT showed an increase of 3.5% and 4.8% in organic carbon contents, related to CT and to RT, respectively.