The challenge of agricultural sector is to reduce greenhouse gas (GHG) emissions while increasing food, fiber and energy production without jeopardizing environmental integrity. In the Andean zone of Colombia, there is a growing need to develop GHG mitigation techniques associated with milk production. The present study focuses on GHG emissions and potential sinks associated with milk production scenarios in the Andean zone of Colombia. The scenarios considered were as follows: conventional agriculture of Pennisetum clandestinum in rotation with potatoes (PRP), improved pastures of Lolium multiflorum (IP) and silvopastoral system of P. clandestinum in association with Acacia decurrens and Trifolium repens (SPS). Based on the IPCC (Guidelines for national greenhouse gas inventories. The intergovernmental panel on climate change, Institute for Global Environmental Strategies, Kanagawa, 2006. http://www.ipcc-nggip.iges.or.jp/ support/Primer_2006GLs.pdf) methodologies, the annual GHG emissions considering a 6-year production cycle included agricultural sources and gasoline consumption related to the most important agricultural phases in the field, and a potential for soil carbon accumulation and biomass carbon fixation in all the studied scenarios. The lowest GHG emissions were estimated in PRP scenario (3684 kg CO 2-eq ha-1 year-1), which also presented additional emissions because of soil carbon losses beyond the lower milk productivity. Highest GHG emissions were observed in IP scenario (7711 kg CO 2-eq ha-1 year-1), which exhibited the highest milk productivity and a considerable potential for soil carbon accumulation that could help to offset its emissions. Nevertheless, SPS scenario,

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Purpose The mineralization/immobilization of nutrients from the crop residues is correlated with the quality of the plant material and carbon compartments in the recalcitrant and labile soil fractions. The objective of this study was to correlate the quality and quantity of crop residues incubated in the soil with carbon compartments and CO 2 -C emission, using multivariate analysis. Materials and methods The experiment was conducted in factorial 4 + 2 + 5 with three replicates, referring to three types of residues (control, sugarcane, Brachiaria, and soybean), and two contributions of the crop residues in constant rate, CR (10 Mg ha −1 residue), and agronomic rate, AR (20, 8, and 5 Mg ha −1 residue, respectively, for sugarcane, soybean, and Brachiaria), evaluated five times (1, 3, 6, 12, and 48 days after incubation). At each time, we determined the CO 2 -C emission, nitrogen and organic carbon in the soil, and the residues. In addition, the microbial biomass and water-soluble, labile, and humic substance carbons fractionated into fulvic acids, humic acids and humin were quantified.Results and discussion Higher CO 2 -C emissions occurred in the soil with added residue ranging from 0.5 to 1.1 g CO 2 -C m −2 h −1 in the first 6 days of incubation, and there was a positive correlation with the less labile organic soil fractions as well as residue type. In the final period, after 12 days of soil incubation, there was a higher relation of CO 2 -C emission with carbon humin. The sugarcane and soybean residue (20 Mg ha −1 ) promoted higher CO 2 -C emission and the reduction of carbon residue. The addition of residue contributed to an 82.32 % increase in the emission of CO 2 -C, being more significant in the residue with higher nitrogen availability. Conclusions This study shows that the quality and quantity of residue added to soil affects the carbon sequestration and CO 2 -C emission. In the first 6 days of incubation, there was a higher CO 2 -C emission ratio which correlates with the less stable soil carbon compartments as well as residue. In the final period of incubation, there is no effect of quality and quantity of residue added to soil on the CO 2 -C emission.

R E S U M OO preparo mecânico do solo é uma das práticas agrícolas que contribuem para o aumento da perda de carbono via emissão de CO 2 do solo (FCO 2 ). Com este trabalho objetivou-se investigar o efeito de três sistemas de preparo do solo na FCO 2 , temperatura e umidade do solo em área de reforma da cultura de cana-de-açúcar. A área experimental foi constituída de três parcelas, cada uma recebendo um dos preparos do solo: preparo convencional (PC), subsolagem convencional (SC) e subsolagem localizada (SL). A FCO 2 , temperatura e a umidade do solo foram avaliadas durante o período total de 17 dias. A FCO 2 foi maior no preparo PC (0,75 g CO 2 m -2 h -1 ). A temperatura do solo não diferiu (p > 0,05) entre as subsolagens: SL (26,2 ºC) e SC (25,9 ºC). A umidade do solo foi maior na SL (24%), seguida pela SC (21,8%) e preparo PC (18,3%). Apenas no preparo PC foi observada correlação significativa (r = -0,71; p < 0,05) entre FCO 2 e a temperatura do solo. O preparo PC apresentou emissão total (2.864,3 kg CO 2 ha -1 ), superior às emissões nas subsolagens: SC (1.970,9 kg CO 2 ha -1 ) e SL (1.707,7 kg CO 2 ha -1 ). A conversão do sistema de preparo PC para a SL diminuiu as emissões de CO 2 do solo, reduzindo a contribuição da agricultura para o aumento dos gases de efeito estufa na atmosfera.Soil tillage and emission of CO 2 , soil temperature and soil moisture in a sugarcane area A B S T R A C TSoil tillage is one of the agricultural practices that may contribute to increase the loss of carbon through emission of CO 2 (FCO 2 ). The aim of this study was to investigate the effect of three soil tillage systems on FCO 2 , soil temperature and soil moisture in a sugarcane area under reform. The experimental area consisted of three tillage plots: conventional tillage (CT), conventional subsoiling (CS), and localized subsoiling (LS). FCO 2 , soil temperature and soil moisture were measured over a period of 17 days. FCO 2 showed the highest value in CT (0.75 g CO 2 m -2 h -1 ). Soil temperature presented no significant difference (p > 0.05) between LS (26.2 °C) and CS (25.9 °C). Soil moisture was higher in LS (24%), followed by CS (21.8%) and CT (18.3%). A significant correlation (r= -0.71; p < 0.05) between FCO 2 and soil temperature was observed only in CT. The conventional tillage presented a total emission (2,864.3 kg CO 2 ha -1 ) higher than the emissions observed in CS (1,970.9 kg CO 2 ha -1 ) and LS (1,707.7 kg CO 2 ha -1 ). The conversion from CT to LS decreased soil CO 2 emissions, reducing the contribution of agriculture in increasing the concentration of greenhouse gases in the atmosphere. Palavras-chave:respiração do solo subsolagem cana-de-açúcar gases do efeito estufa

RESUMOO solo é um dos principais compartimentos de carbono no ecossistema terrestre, capaz de armazenar quantidades expressivas desse elemento e, portanto, a compreensão dos fatores que contribuem para as perdas de CO 2 em solos agrícolas é fundamental para determinar estratégias de redução das emissões desse gás e ajudar a mitigar o efeito estufa. O objetivo deste estudo foi investigar o efeito do preparo do solo e da deposição de resíduos da cultura da cana-de-açúcar na emissão de CO 2 , temperatura e umidade do solo, durante a reforma do canavial, ao longo de um período de 15 dias. Os manejos avaliados foram: sem preparo do solo e mantendo os resíduos da colheita sobre a superfície do solo (SPCR); sem preparo do solo e sem resíduo (SPSR) e com preparo do solo e sem resíduo (CPSR). A menor média de emissão de CO 2 do solo (FCO 2 ) foi observada no manejo SPCR (2,16 µmol m -2 s -1 ), quando comparado aos manejos SPSR (2,90 µmol m -2 s -1 ) e CPSR (3,22 µmol m -2 s -1 ), indicando que as maiores umidades e menores variações da temperatura do solo, observadas em SPCR, foram os fatores responsáveis por tal diminuição. Durante o período de estudo, a menor média diária da FCO 2 foi registrada em SPCR (1,28 µmol m -2 s -1 ) e a maior em CPSR (6,08 µmol m -2 s -1 ), após a ocorrência de chuvas. A menor perda de C-CO 2 do solo foi observada no manejo SPCR (367 kg ha -1 de C-CO 2 ), diferindo significativamente (p<0,05) dos manejos: SPSR (502 kg ha -1 de C-CO 2 ) e CPSR (535 kg ha -1 de C-CO 2 ). A umidade do solo foi a variável que apresentou valores mais diferenciados entre os manejos, sendo positivamente correlacionada (r = 0,55; p<0,05) com as variações temporais da emissão de CO 2 nos manejos SPCR e CPSR. Em adição, a temperatura do solo diferiu (p<0,05) somente no manejo SPCR (24