1 Use of the New Nitrogen Index Tier Zero to Assess the Environmental Effects of 1 Nitrogen Fertilizer Use in Crop Systems of Mexico 2 3 4 Jorge A. Delgado a* , Vinisa Saynes b , Caleb Tebbe a , 5 Jorge D. Etchevers b , Daniel Lapidus c and Adriana Otero-Arnaiz c 6 7 a USDA-ARS, Soil Plant Nutrient Research Unit, Fort Collins, CO 80526; * Corresponding 8 author; b Colegio de Postgraduados, Lab. Fertilidad de Suelos y Química Ambiental, 9 Texcoco, Mexico; c USDA-FAS, 1400 Independence Avenue, SW, Washington, D.C. 10 20250 11 *Corresponding author. USDA, ARS, 2150 Centre Avenue, Building D, Fort Collins, CO 12 80526, United States. Tel: (970) 492-7260; fax: (970) 492-7213; e-mail: 13 jorge.delgado@ars.usda.gov. 14 15 ABSTRACT 16 Mexico is one of the largest users of N fertilizer in the world, and the 2 nd largest 17 user in Latin America after Brazil. Across large areas of Mexico, N fertilizers are being 18 over-applied, resulting in lower N use efficiency. Mexico’s greenhouse gas (GHG) 19 inventory (in CO 2 equivalents) reports that agricultural production contributes to about 12% 20 of the country’s emissions, with N 2 O-N emissions from fertilizer contributing about half of 21 the GHG emissions from agriculture. Mexico does not have tools that can be used to assess 22 Comentario [A1]: The title should reflect the main topic in the manuscript, which is the assessment of nitrous oxide emissions