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 CO 2 -C loss, we studied the infl uence 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 CO 2 -C emissions were measured daily for two weeks after tillage using portable soil respiration systems. Daily CO 2 -C emissions declined after tillage regardless of tillage system. In 2008, total CO 2 -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 CO 2 -C emissions. Regarding the estimated emissions from sugarcane residue and SOC decomposition within the measurement period, CO 2 -C factor was similar to sugarcane residue and soil organic carbon decomposition, depending on the tillage system applied. Our approach may defi ne new emission factors that are associated to tillage operations on bare or sugarcane-residue-covered soils to estimate the total carbon loss.Keywords: soil respiration, carbon dioxide, emission after tillage, soil organic carbon IntroductionLosses of soil organic carbon (SOC) due to soil management in agricultural areas have been identifi ed as a factor that accelerates the greenhouse effect, especially by emitting CO 2 in the atmosphere (Eugster et al., 2010). Losses of SOC can be assessed either by directly measuring changes in SOC content or by monitoring soil CO 2 emissions. The latter has the advantage to detect immediate or near-immediate effects of management practices on C loss via emissions. The impact of tillage on the loss of SOC and associated emission factors under different management systems has been studied (Smith et al., 2010;La Scala et al., 2008; La Scala et al., 2009 a,b), and some researchers have used tillage emission factors as bias for estimating soil conversion from conventional to no-till. However, Smith et al. (2010) noted that this conversion can be affected by the depth of tillage, and multiple factors should be developed to reduce estimation errors.Agricultural activities contribute with approximately 20 % to the global greenhouse gas emissions (Lokupitiya and Paustian, 2006). No-till farming combined with the maintenance of crop residues on the soil surface has been identifi ed as an important strategy for sequestering carbon (C) from the atmosphere (Lal, 2007). Tillage induces the loss of C as CO 2 by breaking up soil aggregates and exposing the protected organic matter to microbes. Tillage also incorporates and mixes residues, improving aeration, which can lead to additional C losses by maximizin...

ABSTRACT:To study Assessing the impact of tillage practices on soil carbon losses dependents it is necessary to describe the temporal variability of soil CO 2 emission after tillage. It has been argued that large amounts of CO 2 emitted after tillage may serve as an indicator for longer-term changes in soil carbon stocks. Here we present a two-step function model based on soil temperature and soil moisture including an exponential decay in time component that is efficient in fitting intermediate-term emission after disk plow followed by a leveling harrow (conventional), and chisel plow coupled with a roller for clod breaking (reduced) tillage. Emission after reduced tillage was described using a non-linear estimator with determination coefficient (R 2 ) as high as 0.98. Results indicate that when emission after tillage is addressed it is important to consider an exponential decay in time in order to predict the impact of tillage in short-term emissions.KEYWORDS: soil respiration, soil CO 2 emission, soil tillage, greenhouse effect. VARIABILIDADE TEMPORAL DA EMISSÃO DE CO 2 DO SOLO APÓS PREPARO CONVENCIONAL E REDUZIDO DESCRITO POR MODELO EXPONENCIAL DECRESCENTE NO TEMPO RESUMO:A quantificação do impacto das práticas de preparo sobre as perdas de carbono do solo é dependente da habilidade de se descrever a variabilidade temporal da emissão de CO 2 do solo após preparo. Tem sido sugerido que as grandes quantidades de CO 2 emitido após o preparo do solo podem servir como um indicador das modificações nos estoques de carbono do solo em longo termo. Neste trabalho é apresentado um modelo de duas partes baseado na temperatura e na umidade do solo e que inclui um termo exponencial decrescente do tempo que é eficiente no ajuste das emissões intermediárias após preparo: arado de disco seguido de uma passagem com a grade niveladora (convencional) e escarificador de arrasto seguido da passagem com rolo destorroador (reduzido). As emissões após o preparo do solo são descritas utilizando-se estimativa não linear com um coeficiente de determinação (R 2 ) tão alto quanto 0.98 após preparo reduzido. Os resultados indicam que nas previsões da emissão de CO 2 após o preparo do solo é importante considerar um termo exponencial decrescente no tempo após preparo. PALAVRAS-CHAVE:respiração do solo, emissão de CO 2 do solo, preparo do solo, efeito estufa.

Soil tillage is a process that accelerates soil organic matter decomposition transferring carbon to atmosphere, mainly in the CO 2 form. In this study, the effect of rotary tillage on soil CO 2 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 CO 2 m -2 h -1 ), with the lowest emissions recorded in the NTwo plot (0.414 g CO 2 m -2 h -1 ). Total emission indicates that the difference of C-CO 2 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 CO 2 emission, and soil temperature and soil moisture is considered, only the RTw treatment showed significant correlation (p<0.05) with soil moisture.KEYWORDS: soil respiration, soil tillage, carbon dioxide, temporal variability of soil CO 2 emission. EMISSÃO DE CO 2 DO SOLO EM FUNÇÃO DA INCORPORAÇÃO DE PALHA DE CANA-DE-AÇÚCAR E QUEBRA DE AGREGADOS APÓS PREPARO COM ENXADA ROTATIVARESUMO: O preparo do solo é um dos processos que aceleram a decomposição da matéria orgânica, transferindo carbono para atmosfera, principalmente na forma de CO 2 . Neste trabalho, investigou-se o efeito do preparo com enxada rotativa sobre as emissões de CO 2 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 CO 2 m -2 h -1 ), sendo as menores emissões registradas na parcela SPs (0,414 g CO 2 m -2 h -1 ). As emissões totais indicaram que a diferença de C-CO 2 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 an...

Este trabalho avaliou o impacto do preparo em diferentes configurações sobre as emissões imediatas de CO2 do solo, empregando dois dos principais sistemas de preparo utilizados em áreas agrícolas: arado de disco seguido de grade niveladora (convencional) e escarificador conjugado com rolo destorroador (reduzido). Os resultados indicaram maiores emissões induzidas pelo preparo convencional, arado de disco seguido de grade niveladora, num total de 260,7 gramas de CO2 m-2 no período de 14 dias de estudo. Por outro lado, as menores emissões foram observadas após preparo com escarificador sem a utilização do rolo destorroador, de 82,3 gramas de CO2 m-2. Os fatores temperatura e umidade do solo não se relacionaram com as variações do fluxo de CO2 do solo, mas o tempo foi um fator importante na capacidade de previsão da emissão após preparo do solo.