Use of the new Nitrogen Index tier zero to assess the effects of nitrogen fertilizer on N2O emissions from cropping systems in Mexico

Mexico is one of the largest users of N fertilizer in the world, and the 2nd largest user in Latin America after Brazil. Across large areas of Mexico, N fertilizers are being over-applied, resulting in lower N use efficiency. Mexico's greenhouse gas (GHG) inventory (in CO2 equivalents) reports that agricultural production contributes to about 12% of the country's emissions, with N2O-N emissions from fertilizer contributing about half of the GHG emissions from agriculture. Mexico does not have tools that can be used to assess N fertilizer use and emissions of N2O-N from organic and inorganic sources. Such tools could be used to help nutrient managers implement management practices that increase N use efficiencies and reduce N2O-N emissions. The new Nitrogen Index tier zero tool was used to assess N use efficiencies and N2O-N emissions in different cropping systems of Mexico. Mexico's current GHG inventory for agriculture just multiplies the use of N fertilizer in the country by 1% to assess national emissions of N2O. When we tested the new tier zero Nitrogen Index, it performed much better than the current methodology for calculating Mexico's N2O emissions, and N2O emissions predicted by the tool were correlated with observed values (P < 0.01). The N index tool was closer to measured values than the current method used for Mexico's GHG inventory. We propose that this prototype of the Nitrogen Index tier zero for Mexico can be used to assess the effects of cropping systems and N management practices on emissions of N2O-N in Mexico to improve the accuracy of the national inventory of N2O-N emissions in Mexico, which is reported to the United Nations Framework Convention on Climate Change (UNFCCC). Additionally, the tool can also be used to assess N management practices to increase N use efficiency with just a minimal amount of information provided by the user.