Colombia is one of the countries with the highest livestock inventory of Latin America, much of which is under extensive grazing of Brachiaria spp., Megathyrsus maximus and native pastures. The quantitative contribution of this sector to our national Greenhouse Gases (GHGs) emissions, particularly nitrous oxide (N2O) emissions, need a better approach to real fluxes. Some Brachiaria species are natural producers of Biological Nitrification Inhibitors (BNI), which are an alternative mitigation of GHGs in field. However, not all tropical grasses produce the same quantity of BNI (1). The objective of this research was to quantify N2O emissions from ruminant urine in different pastures both during dry and rainy seasons.