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

Authors: SAYNES, VINISA - Colegio De Postgraduados; Delgado, Jorge; Tebbe, Caleb; ETCHEVERS, JORGE - Colegio De Postgraduados; LAPIDUS, DANIEL - Foreign Agricultural Service (FAS, USDA); OTERO-ARNAIZ, ADRIANNA - Colegio De Postgraduados

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2014
Publication Date: 10/22/2014
Citation: Saynes, V., Delgado, J.A., Tebbe, C., Etchevers, J.D., Lapidus, D., Otero-Arnaiz, A. 2014. Use of the new Nitrogen Index tier zero to assess the effects of nitrogen fertilizer on N2O emissions from cropping systems in Mexico. Ecological Engineering. 73:778-785.

Interpretive Summary: Mexico is one of the largest users of N fertilizer in Latin America, and the emissions of N2O are a significant source as far as their CO2 equivalent emissions reported to the UNFCCC. The methodology used by Mexico’s greenhouse gas inventory only assumes that 1% of the N fertilizer is emitted as N2O. The Nitrogen Index Tier Zero tool requires little information to assess the effects of N management practices on N2O emissions and N dynamics. The Nitrogen Index’s predictions of N2O emissions were closer to observed values than the current methodology being used by the Mexico’s greenhouse gas inventory. The Nitrogen Index Tier Zero tool was capable of estimating the trends in N2O emissions, crop N uptake, and N use efficiency in different cropping systems (P<0.05). The results suggest that the tool is capable of evaluating N dynamics in Mexican agricultural systems and is an improved method of assessing N2O emissions from Mexican cropping systems. Nitrogen fertilizers are important for agricultural production in Mexico, but when N fertilizer is over-applied it can contribute to higher N losses. This tool has the potential to help its users evaluate N management practices, assess crop N uptake and N use efficiency in the system, and assess the potential to reduce N2O emissions.

Technical Abstract: 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 efficiencies. Mexico’s trace gas inventory (in CO2 equivalents) reports that agricultural production contributes to about 12% of the country’s emissions, with N2O-N contributing about half of the trace gas 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 trace gas 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 greenhouse gas 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 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.