Mineralizable carbon, organic carbon and nitrogen in macroaggregates of an Oxisol under different systems soil usages in Cerrado Goiano

The crop-livestock integration system (CLIS) associated to a no-tillage system (NTS) may increase mineralizable carbon, organic carbon and nitrogen of soil macroaggregates when compared with only NTS area, without grazing. The aim of this study was to quantify mineralizable carbon, total organic carbon (TOC) and nitrogen of macroaggregates in different land management systems in Cerrado region, Goias State. There were evaluated two areas with crop rotation: CLIS (Brachiaria+corn/bean/cotton/soybean) and NTS (sunflower/millet/soy/corn). A Cerrado area with natural vegetation was taken as reference for the original soil. Undisturbed soil samples were taken at 0-5 and 5-10 cm depth, and then incubated in laboratory, with the samples set in a randomized design. There were evaluated the C-CO2 detached daily (up to 37 days) from each sample and total respiration of C-CO2 accumulated were also analyzed. Before and after incubation of soil aggregates (0 to 5 and 5 to 10 cm), the TOC, N and C/N were quantified. The CLIS samples showed higher C-CO2 (0-5 cm) immediately after incubation when compared to other samples. At 7 days after incubation, in the three systems, there was an increase of C-CO2 liberation and, after the 25th day the microbial respiration was stabilized. Comparing the cultivated areas, CLIS showed higher C-CO2 accumulation and the highest TOC, N (before and after incubation), and lower C/N ratio, before incubation. The CLIS increased higher C-CO2 accumulations than the NTS area. The integration of the factors crop rotation, cover crops (brachiaria) and cattle grazing in the CLIS increase mineralizable carbon (C-CO2 accumulations), TOC and N in macroaggregates compared to the NTS area.