The Influence of Agricultural Systems on Greenhouse Gas Emissions in the Eastern High Plains of Colombia.

The Eastern high plains of the Orinoco River basin is considered the last agricultural frontier in Colombia, because of its potential to extend the agro-industrial production areas. Soil management plays an important role in the sustainability of proposed agricultural systems. The objective of this work was to quantify greenhouse gas (GHG) emissions from agricultural systems under different management practices aimed at improving soil physical and chemical properties. The experiment was established in 2011 at Corpoica’s experimental station in Taluma (Meta, Colombia). The experiment was organized in a split-split plot design in which the main plot was the cropping system (corn-soybean rotation, pasture-crop, sugarcane, and native savanna - control). The sub-plot was the tillage method for lime incorporation (moldboard plow, chisel plow and disk plow) and the sub-sub plot was the lime amendment dose (3 and 6 t ha^-1). Tillage and lime amendments were applied at the beginning of the experiment. The air samples were collected monthly using the static chamber method and the concentration of nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄) were quantified through gas chromatography. Fluxes of the different GHG’s were estimated using linear and non-linear approaches (HMR library from R statistical software). The fluxes were tested for temporal correlation and then analyzed using the repeated measures approach (proc glimmix SAS v. 9.3). The Aikaike Information Criterion (AIC) was used to compare model performances. We report here results for the 2014 and 2015 growing season. Overall, GHG emissions fluctuated during the study years in response to management practices and precipitation events. Regarding cumulative emissions there were no tillage and lime amendment effects. However, significant differences of cumulative emissions were detected among systems and years. Overall, the emissions were higher in 2015 than 2014 in which the highest N₂O emissions were observed under the pasture-crop system followed by corn-soybean rotation. Sugarcane and native savanna had similar emissions of CO₂ and N₂O during the study period. For CH₄ most of the systems acted as a sink instead of source, except for sugarcane. The lowest emissions were detected under the native savanna plots. Nitrous oxide emissions were enhanced by N fertilization which make it an important GHG in the agricultural systems of the eastern plains region of Colombia. We conclude that future monitoring campaigns should focus on N₂O emissions associated with fertilization and explore mitigation actions that improve nitrogen use efficiencies.