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Revista mexicana de ciencias agrícolas
versión impresa ISSN 2007-0934
Rev. Mex. Cienc. Agríc vol.8 no.8 Texcoco nov./dic. 2017
https://doi.org/10.29312/remexca.v8i8.698
Articles
Emission of greenhouse gases from nitrogen fertilization in Mexico
1Campo Experimental Valle de México-INIFAP. Carretera Los Reyes-Texcoco km 13.5, Texcoco, Estado de México, CP. 56250.
2Universidad Autónoma Chapingo Posgrado de Economía Agrícola y de los Recursos Naturales. Chapingo, Estado de México. CP. 56230.
Mexican agriculture is an important source of greenhouse gases, mainly through nitrogen fertilization that emits an important greenhouse gas: nitrous oxide, which represents 50.4% of the emissions of the sector in equivalent units of carbon dioxide. However, the importance of such emissions, reliable estimates are not available. The objective of this research was to quantify the emissions of greenhouse gases produced by nitrogen fertilization in Mexican agriculture, during the period 1980-2014. The method followed for the quantification of these emissions is the one proposed by: the environmental protection agency of the United States of America (USA), the Intergovernmental Panel on Climate Change and the Food and Agriculture Organization of the United Nations. The total applications of the different nitrogenous fertilizers in Mexican agriculture from 1980 to 2014 were quantified and nitrous oxide emissions and their conversion into equivalent units of carbon dioxide were estimated. It was concluded that the use of chemical fertilizers in Mexican agriculture is inefficient, because the costs of nitrous oxide emissions are not taken into account when deciding the amount of nitrogen to be applied per hectare. Consequently, the costs of nitrous oxide emissions produced by nitrogenous chemical fertilizers must be quantified and, based on this, an efficient policy for the application of fertilizers and for abatement of the emissions they produce must be defined.
Keywords: Mexican agriculture; nitrogen fertilizers; nitrous oxide
La agricultura mexicana es una fuente importante de gases de efecto invernadero, principalmente a través de la fertilización nitrogenada que emite un importante gas de efecto invernadero: el óxido nitroso, el cual representa 50.4% de las emisiones del sector en unidades equivalentes de bióxido de carbono. No obstante, la importancia de tales emisiones, no se dispone de estimaciones fidedignas. El objetivo de ésta investigación fue cuantificar las emisiones de gases de efecto invernadero producidas por la fertilización nitrogenada en la agricultura mexicana, durante el período 1980-2014. El método seguido para la cuantificación de esas emisiones es el propuesto por: la agencia para la protección ambiental de Estados Unidos de Norteamérica (EE.UU), el Panel Intergubernamental del Cambio Climático y la Organización para la Alimentación y la Agricultura de las Naciones Unidas. Se cuantificaron las aplicaciones totales de los distintos fertilizantes nitrogenados en la agricultura mexicana de 1980 a 2014 y se estimaron las emisiones de óxido nitroso y su transformación en unidades equivalentes de bióxido de carbono. Se concluyó que el uso de fertilizantes químicos en la agricultura mexicana es ineficiente, debido a que no se toman en cuenta los costos de las emisiones de óxido nitroso a la hora de decidir la cantidad de nitrógeno que se aplicará por hectárea. En consecuencia, se deben cuantificar los costos de las emisiones de óxido nitroso producidas por los fertilizantes químicos nitrogenados y definir, con base en ello, una política eficiente para la aplicación de fertilizantes y para el abatimiento de las emisiones que producen.
Palabras clave: agricultura mexicana; fertilizantes nitrogenados; óxido nitroso
Introduction
Global warming and the resulting climate change are a reality whose intensity is growing. In the last sixty years, an increasing warming of the atmosphere and water of the oceans, a reduction of the surface covered with ice and an increase in the level of the seas has been observed at planetary level. The main cause is the set of productive activities of the current society.
Mexico, due to its geographical physical characteristics, will be one of the countries most affected by climate change, because it is located between two large oceans, at the latitude where the great deserts of the world are located, and has large mountain systems. In terms of the effects of these climate changes, Mexico will see its agricultural production capacity reduced by 27% by the year 2050 (Cline, 2008); the productivity in the cultivation of corn and beans will decrease and there will be a loss of fertility in the soils of 25% of the production units. By the year 2030 it is forecast that the prevailing natural conditions will be less conducive to the production of most crops. This situation will worsen at the end of this century (DOF, 2014). The negative economic impacts caused by extreme hydrological and meteorological phenomena will grow. The losses caused by these phenomena went from an annual average of 730 million pesos during the period 1980-1999 to 21 950 million pesos per year in the period 2000-2012 (SEMARNAT, 2013).
In 2012, the productive and social activity of humanity produced 52.76 gigatons of carbon dioxide equivalent (Gt CO2 eq), according to the Oak Ridge National Laboratory (2015). Mexico contributes 1.3% to the total. Mexican agriculture and livestock contribute 12.3% to the country’s total greenhouse gas (GEI) emissions, mainly through nitrogen fertilization that emits an important greenhouse gas: nitrous oxide (N2O), which contributes 50.4% of all emissions in the sector.
Nitrous oxide emissions (N2O) are generated by natural processes and by the leaching, volatilization and runoff of nitrogen fertilizers, as well as the decomposition of crop and animal waste. According to the Food and Agriculture Organization (FAO, 2002), China is the largest consumer of nitrogen fertilizers in the world and loses 57.5% of all nitrogen applied in agriculture, due to 50% volatilization and 7.5% % to infiltration. In Mexico, nitrous oxide emissions N2O in 2014 were 22 860.1 t. The contribution of the different emitting sources is: agricultural soils 67.2% (mainly from the application of nitrogen fertilizers), transport 18.2%, manure management 9.3%, treatment and disposal of wastewater 2.8% and other sources 2.5 % (SEMARNAT-INECC, 2013). Globally, the use of nitrogen fertilizers in agriculture has grown very rapidly, so it is expected that the corresponding emissions will increase 50% by the year 2030.
Despite the importance of nitrous oxide emissions produced by chemical fertilization in Mexican agriculture, there is no reliable estimate of its magnitude.
Ruiz (2011), used the input-output matrix of Mexico in 2003 and the information from the National Inventory of Greenhouse Gases 1990-2002 of SEMARNAT-INE (2006) to estimate the costs of greenhouse gas emissions of each of the 79 economic branches. With this information, it calculated the vector of the emission coefficients by branch, normalizing the emission values with respect to the gross value of the 2003 production based on the method suggested by the Intergovernmental Panel on Climate Change (IPCC). This percentage structure was applied to the total emissions of 2003, reported by the Institute of Ecology. Thus, it obtained the GEI emissions for each sector or sub-sector. Then, the categories of the IPCC classification were made compatible with the branches of the input-output matrix, by distributing the emissions in each branch by their relative share in the gross value added within the corresponding sector in the same year (2003).
Another procedure based on average coefficients is the one used to obtain the estimates contained in the national inventory of greenhouse gases 1990-2010 SEMARNAT (2013a). Table A.3.3 of annex A of the National Inventory of Greenhouse Gas Emissions 1990-2010 of SEMARNAT (2013a), which presents estimates of nitrous oxide emissions produced by the application of such fertilizers in Mexico, is based on the assumption that nitrogenous synthetic fertilizers have 34.5% active nitrogen, “which is the value of the national average”. That coefficient is wrong and consequently, the estimates in Table A.3.3 based on it are also wrong. This statistical error also distorts the estimates that appear in the FAOSTAT database (2016). In the case of nitrous oxide emissions produced by the application of nitrogenous chemical fertilizers, this error produces estimates with considerable errors. The source of these estimation errors is that coefficients based on a simple average of the nitrogen content in the different nitrogen fertilizers (34.5%) were used, instead of using a weighted average of the apparent national consumption of the same, as it would have been the right thing.
After taking into account the aforementioned statistical errors, and aware of the importance of contributing to the fulfillment of emission reduction targets at national and global levels, this research proposed the objective of estimating, with greater rigor and precision , the annual emissions of nitrous oxide (N2O) produced by nitrogenous fertilization in Mexican agriculture during the period 1980-2014, taking into account the most recent versions of the equations used to estimate nitrous oxide emissions.
Materials and methods
Reference parametric base
The main cause of global warming is the concentration in the atmosphere of greenhouse gases that maintain infrared radiation from the earth’s surface, which increases the air temperature. The greenhouse gases are: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), chlorofluorocarbons (CFC), water vapor and others. The first three gases together accounted for 99% of emissions and the last three 1%, in 2002. The role played by carbon dioxide is very important for life, because if it did not exist, the average temperature on Earth would be -18 °C and, on the contrary, a higher concentration at a certain point will warm the atmosphere in a very significant way (Uzawa, 2010). The latter is what has been happening.
The most important greenhouse gases produced by human activities are: carbon dioxide CO2, emitted by the consumption of fossil fuels and industrial activities represents 65% of total emissions, methane CH4, represents 16%, carbon dioxide CO2, produced by agriculture, livestock and forestry 11%, nitrous oxide N2O 6%, and fluorinated gases or F gases (6%) (IPCC, 2014a). In terms of emissions by sector, measured in units equivalent to carbon dioxide (CO2 eq), electricity and heat production contributed 25%, agriculture, livestock and forestry 24%, industry with 21%, transportation 14 %, commercial and residential buildings with 6% and other emissions from the energy sector 10% (IPCC, 2014a).
According to the IPCC (2014a), the concentration in the atmosphere of greenhouse gases (GEI) produced by nature has fluctuated in the last 650 000 years, as periods of warming and cooling of the land alternate. In the 1 000 years prior to 1750 CO2 levels never increased beyond 30 parts per million (ppm). However, in the last two decades the increase was greater. At the beginning of the industrial revolution in 1750, the concentration of carbon dioxide in the atmosphere was 280 parts per million (ppm). However, in 1960 it was 315 and in 2010 it was 380 (Sachs, 2008). Half of the accumulated emissions of CO2 between 1750 and 2012 have occurred in the last 42 years.
That process of growth of emissions continues to accelerate. From 1970 to 1999, the emissions of these gases, measured in giga tonnes of carbon dioxide equivalent (Gt CO2 eq), grew at an annual rate of 1.64%, while from 2000 to 2012 they grew at a rate of 2.69% per year (IPCC, 2014). These data contrast sharply with all the rhetoric used by most countries to highlight their GHG emission control programs and society today is acting very irresponsibly.
In 2012, the productive and social activity of humanity produced 52.76 gigatons of carbon dioxide equivalent (Gt CO2 eq) (ORNL, 2015). The countries with the highest emissions are: China (23.6%), USA (12%), India (5.7%), Brazil (5.7%), Russian Federation (5.3%), Arab Countries (4.9%), Japan (2.8%), Germany (1.8%) and Mexico (1.3%). China produces almost a quarter of global emissions. Note that China, India, Brazil, the Russian Federation, the Arab World and Mexico contribute 46.4%.
Between 1970 and 2012 the country increased its greenhouse gas emissions from 210.5 to 663.4 million tons in units of carbon dioxide equivalent. This last number is equivalent, simply, to 0.6634 Gt CO2 eq. According to SEMARNAT-INECC (2013), emissions in 2010 were 748.3 million tons and not 663.4. In just 42 years, emissions multiplied 3.15 times in relation to the base year. According to the World Bank database (World Bank, 2013), emissions per capita in Mexico of carbon dioxide alone, CO2, were 1.64 t in 1960, 2.2 in 1970, 3.7 in 1990 and 3.9 t in 2013 , which means that between 1960 and 2013, emissions in Mexico multiplied 2.38 times, at an average annual rate of growth of 4.59%. However, total greenhouse gas emissions were 7.1 t of CO2 eq.
According to the National Inventory of Greenhouse Gases 1990-2010 (SEMARNAT-INECC, 2013), of the total national greenhouse gas emissions, converted to equivalent units of carbon dioxide, CO2 eq, the energy sector contributed 21.8%, transportation 22.2%, agriculture and livestock 12.3%, fugitive emissions 11.1%, industry 8.2%, manufacturing and construction industry 7.6%, land use, changes in land use and forestry 6.3%, waste 5.9% and the commercial and residential sector 4.6%.
Emissions of nitrous oxides (N 2 O), in terms of carbon dioxide equivalent (CO 2 eq), produced by the application of nitrogen fertilizers
In order to quantify the nitrous oxide emissions (N2O) produced by nitrogen fertilization in Mexican agriculture, information was first gathered on the annual application of the different types of nitrogen fertilizers in the Mexican Republic. Subsequently, the equivalent nitrogen content was calculated for each of the fertilizer classes applied. Afterwards, the N2O emissions were estimated for the consumption of nitrogen fertilizers. Finally, these emissions were expressed in units of carbon dioxide equivalent (CO2 eq).
The application of nitrogenous chemical fertilizers produces direct (ED) and indirect (EI) emissions of nitrous oxide. The direct emission of nitrous oxide is produced by two microbiological processes: nitrification, which is an oxidation of ammonium to nitrate and denitrification, which is a reduction of nitrate to the gaseous forms of nitrogen, N2O and N2. Then, indirect emissions are produced through the processes of volatilization/redeposition and leaching. In order to estimate the direct emissions (ED) of N2O associated with the application of nitrogen fertilizers in agriculture, the method developed by the Environmental Protection Agency (EPA, 1992) of the USA, FAO ( 2014) and the Intergovernmental Panel on Climate Change (Klein, 2006), which is summarized in the following conversion equation.
Where: CF is the fertilizer consumption in tons of applied active nitrogen, CE represents the coefficient or emission factor and the fraction (44/28)= 0.01571429 represents the molecular weight of N2O in relation to the nitrogen molecules contained in the nitrous oxide (N2O/N2O-N); that is, this expression represents the molecular weight ratio of N2O: the number 44 is the total sum of molecular weights of its two nitrogen molecules which is 28 and oxygen, which is 16, and the number 28 is the molecular weight of N2
The agricultural research service of the US Department of Agriculture estimated in 1990 that 100 kg of nitrogen applied as fertilizer emit 1.84 kg of N2O. The US Environmental Protection Agency. (EPA, 1992) estimated an emission coefficient (CE) equal to 0.0117 t of N2O per ton of nitrogen applied, which means that 1.17% of the nitrogen applied as fertilizer is released to the atmosphere as N2O. The coefficient of emissions used by FAO (2012) is 0.0125. The estimate by Davidson (2009) is 0.01458. According to Shcherbak et al. (2014) the average emission coefficient of 1000 measurements in the field is equal to 0.01. The estimator used here is CE = 0.01, which was obtained by Klein (2006) and reported in the guidelines for the greenhouse gas inventory of the Intergovernmental Panel on Climate Change.
Nitrous oxide is a very powerful greenhouse gas (GEI) and its global warming potential (GWP) is 310, which means that each tonne of nitrous oxide equals 310 tonnes of carbon dioxide (SEMARNAT, 2013a). According to the EPA (1992), the formula for transforming direct emissions of nitrous oxide into carbon dioxide equivalent (CO2 eq) is as follows.
On the other hand, the indirect emissions (EI) of nitrous oxide produced by nitrogen fertilizers are determined as follows, according to the guidelines of the Intergovernmental Panel on Climate Change (Klein, 2006).
Where: FraccGASF is the fraction of applied nitrogenous fertilizer that is volatilized in the form of ammonia (NH3) and in different forms of nitric oxide (NOX); CE4 is the coefficient of indirect emissions from volatilization; FraccLEACH represents the amount of active nitrogen applied that is leached, and CE5 is the coefficient of indirect emissions from leaching. According to the parameters contained in Tables 24-28 of (FAO, 2014), the previous expression is transformed into the following.
The formula used to transform the indirect emissions of nitrous oxide into carbon dioxide equivalent (CO2 eq)is as follows.
Finally, the total emissions (ET) of nitrous oxide, in units of CO2 eq produced by the application of nitrogen fertilizers, are the sum of direct and indirect emissions. That is to say:
Statistical sources
The calculation of N2O emissions in terms of CO2 eq for Mexico was based on the apparent national consumption dynamics of nitrogen fertilizers expressed in tons of active nitrogen, during the period 1980-2014, for which the base of data FAOSTAT (2016). The following statistical sources were also reviewed: 1) the National Inventory of greenhouse gas emissions (INEGEI) for the period 1990-2010; 2) the greenhouse gas (GEI) inventory of agriculture 1990-2010; 3) the reports of the fourth national communication; 4) the reports of the Environmental Protection Agency of the United States (EPA, 1992); 5) the Statistical Yearbook of the Economic Commission for Latin America (CEPAL, 2011); 6) the agrifood information system for consultation (SIACON) (1980-2012); and 7) the statistics of carbon market facilitators, such as Thomson Reuters Point Carbon, among others.
The documents consulted to obtain statistics were the following: a) the distribution of climate change among the sectors of the Mexican economy (SEMARNAT, 2009a; 2013a), where the impact of polluting gas emissions on the production of 79 branches is evaluated economic and b) the economic estimate of the interrelations of climate change with agriculture and land degradation (SEMARNAT, 2009b; 2013).
Results
The estimators of the nitrous oxide emissions produced by the applications of nitrogenous chemical fertilizers in Mexican agriculture are presented in Tables 1 and 2.
Table 1 Apparent consumption of nitrogen fertilizers in tons of active N and emissions N2O in Mexico, 1980-1996.
Table 2 Apparent consumption of nitrogen fertilizers in tons of active N and nitrous oxide emissions (N2O) in Mexico, 1997-2014.
The estimates of nitrous oxide emissions expressed in units equivalent to carbon dioxide produced by the applications of nitrogenous chemical fertilizers in Mexican agriculture are presented in Tables 3 and 4.
Table 3 Apparent consumption of nitrogen fertilizers in tons of active N and nitrous oxide emissions (N2O) in units of CO2 eq in Mexico, 1980-1996.
Discussions
The results presented in Tables 1 to 4 on the consumption of active nitrogen are more credible, close to reality and reliable, than those reported by SEMARNAT (2013a) and by FAOSTAT (2016), due to the inadequate statistical procedures they applied. The assumption that nitrogenous synthetic fertilizers have an average of 34.5% of active nitrogen, is false, because it is a simple arithmetic mean of the N content in the different nitrogen fertilizers, being correct to calculate a weighted average of the N content of the national consumption apparent of the different nitrogen fertilizers, taking into account the different percentage of N that each of the nitrogen fertilizers has and the quantities consumed of each product. For this reason, the estimates in Table A.3.3 of SEMARNAT (2013a) are erroneous.
After applying the Hodrick-Prescott filter (1997) to the time series of apparent consumption of nitrogen based chemical fertilizers in Mexico, it was observed that the secular trend of that variable grew from 1980 to 1989 -this year in which the real beginning is considered. The most non-formal of the North American Free Trade Agreement (NAFTA)- and began to decrease from 1990, from the year 2012 began to grow again. It was also observed that the series of the apparent consumption of nitrogenous synthetic fertilizers fluctuates irregularly in relation to this secular trend. As expected, the corresponding time series of nitrous oxide emissions and that expressed in unit’s equivalent to carbon dioxide have an analogous behavior, as shown in the following Figure 1.
Conclusions
The use of nitrogenous chemical fertilizers in Mexican agriculture is inefficient economically, socially and environmentally. The costs of nitrous oxide emissions produced by nitrogenous chemical fertilizers must be quantified and, based on this, an efficient fiscal-environmental policy for abatement of emissions must be defined.
The Mexican government should include economic, social and environmental impact studies in its strategies and development programs to identify and quantify the costs of negative externalities, generated by the different productive activities, in order to implement optimum-economic solutions that are also efficient from the point of view of social welfare and the need to adapt to climate change.
In the last 30 years in the programs of high yields an excessive use of fertilizers has been promoted, beyond the optimum-economical dose of fertilization and in addition, the cost of nitrous oxide emissions produced by nitrogen chemical fertilizers has not been considered. In general, there is a process of over-intensification of agriculture in the most advanced regions of Mexico, which is not only evidence of inefficiency and waste, but also shows an irresponsible orientation towards society and its well-being.
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Received: October 2017; Accepted: November 2017
Este es un artículo publicado en acceso abierto bajo una licencia Creative Commons
