Appropriate management of agricultural crop residues could result in increases on soil organic carbon (SOC) and help to mitigate gas effect. To distinguish the contributions of SOC and sugarcane (Saccharum spp.) residues to the short-term CO2-C loss, we studied the influence of several tillage systems: heavy offset disk harrow (HO), chisel plow (CP), rotary tiller (RT), and sugarcane mill tiller (SM) in 2008, and CP, RT, SM, moldboard (MP), and subsoiler (SUB) in 2009, with and without sugarcane residues relative to no-till (NT) in the sugarcane producing region of Brazil. Soil CO2-C emissions were measured daily for two weeks after tillage using portable soil respiration systems. Daily CO2-C emissions declined after tillage regardless of tillage system. In 2008, total CO2-C from SOC and/or residue decomposition was greater for RT and lowest for CP. In 2009, emission was greatest for MP and CP with residues, and smallest for NT. SOC and residue contributed 47 % and 41 %, respectively, to total CO2-C emissions. Regarding the estimated emissions from sugarcane residue and SOC decomposition within the measurement period, CO2-C factor was similar to sugarcane residue and soil organic carbon decomposition, depending on the tillage system applied. Our approach may define new emission factors that are associated to tillage operations on bare or sugarcane-residue-covered soils to estimate the total carbon loss.

O preparo do solo é um dos processos que aceleram a decomposição da matéria orgânica, transferindo carbono para atmosfera, principalmente na forma de CO2. Neste trabalho, investigou-se o efeito do preparo com enxada rotativa sobre as emissões de CO2 do solo durante 02 semanas após o preparo do solo, incluindo-se a presença de resíduos vegetais sobre a superfície. As emissões foram avaliadas por 15 dias após preparo em 3 parcelas: 1) sem preparo e sem palha superficial (SPs); 2) preparo com enxada rotativa sem a presença de palha na superfície (ERs), e 3) preparo com enxada rotativa com a presença de palha superficial (ERc). As emissões provenientes da ERc foram superiores às demais (0,777 g CO2 m-2 h-1), sendo as menores emissões registradas na parcela SPs (0,414 g CO2 m-2 h-1). As emissões totais indicaram que a diferença de C-CO2 emitida à atmosfera corresponde a 3% do total de carbono adicional presente na palha, na parcela ERc, quando comparado à parcela ERs. O aumento da emissão da parcela SPs para ERs foi acompanhado de uma modificação na distribuição do tamanho de agregados, especialmente aqueles com diâmetro médio inferior a 2 mm. O aumento da emissão da parcela ERs para ERc esteve relacionado a uma diminuição da massa de palha na superfície, com fragmentação e incorporação da mesma no interior do solo. Quando se analisa a correlação linear entre emissão de CO2 versus temperatura e umidade do solo, somente a emissão da ERc foi significativamente correlacionada (p<0,05) à umidade do solo.

Soil tillage is a process that accelerates soil organic matter decomposition transferring carbon to atmosphere, mainly in the CO2 form. In this study, the effect of rotary tillage on soil CO2 emission was investigated, including the presence of crop residues on the surface.Emissions were evaluated during 15 days after tillage in 3 plots: 1) non-tilled and without crop residues on soil surface (NTwo), 2) rotary tiller without the presence of crop residues on soil surface (RTwo), and 3) rotary tiller with the presence of crop residues in soil surface (RTw). Emissions from the RTw plot were higher than the other plots, (0.777 g CO2 m-2 h-1), with the lowest emissions recorded in the NTwo plot (0.414 g CO2 m-2 h-1). Total emission indicates that the difference of C-CO2 emitted to atmosphere corresponds to 3% of the total additional carbon in the crop residues in the RTw plot compared to RTwo. The increase in the RTwo emission in comparison to NTwo was followed by changes in the aggregate size distribution, especially those with average diameter lower than 2 mm. The increase in emission from the RTw plot in relation to RTwo was related to a decrease in crop residue mass on the surface, and its higher fragmentation and incorporation in soil. When the linear correlation between soil CO2 emission, and soil temperature and soil moisture is considered, only the RTw treatment showed significant correlation (p<0.05) with soil moisture.