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Revista mexicana de ciencias agrícolas

versão impressa ISSN 2007-0934

Rev. Mex. Cienc. Agríc vol.8 no.4 Texcoco Jun./Jul. 2017 


Fossil fuels and CO 2 e in traditional milpa and monoculture maize systems in Tlaxcala, Mexico

Primo Sánchez-Morales1 

Omar Romero-Arenas1  § 

1Centro de Agroecología-Instituto de Ciencias-Benemérita Universidad Autónoma de Puebla (BUAP). 14 sur 6301. Ciudad Universitaria, Puebla, Puebla. CP. 72570. Tel. 01(222) 229550.


A comparative study was carried out between two management systems in maize production in Tlaxcala: traditional milpa system (SMT) versus monoculture maize system (SMo). The objective was to determine the amount of fossil fuel energy that is used during the production process and the emission of carbon dioxide equivalent (CO2e). The efficiency of each system and the emission of the main greenhouse gas (GHG) was estimated. To generate primary information, a mixed methodology was applied: a semi-structured interview was conducted with 20 producers and a sample size for the survey application was calculated from data from the Proagro Productivo 2014 program, where N= 29 828 and n= 379. After collecting the information, a database was prepared in Excel, coded and processed with the SPSS-16 program. The results show that the highest expenditure of fossil energy in both groups occurs during the harvest and is lower in tillage tasks. However, in this item the energy expenditure derived from oil is twice as great in the SMo. Moreover, energy expenditure calculated and CO2e emission are 30.8% higher in the SMo versus the SMT for the same amount of maize produced in each system. It was concluded that although the SMT requires more labor and animal traction force, it is more efficient in the use of fossil energy and the calculated GHG emissions are lower.

Keywords: agriculture; efficiency; energy; productivity


Se realizó un estudio comparativo entre dos sistemas de manejo en la producción de maíz en Tlaxcala: sistema milpa tradicional (SMT) versus el sistema de maíz en monocultivo (SMo). El objetivo fue conocer la cantidad de energía de origen fósil que se emplea durante el proceso de producción y la emisión de dióxido de carbono equivalente (CO2e). Se estimó la eficiencia de cada sistema y la emisión del principal gas de efecto invernadero (GEI). Para generar información primaria se aplicó una metodología mixta: se realizó entrevista semiestructurada con 20 productores y se calculó un tamaño de muestra para la aplicación de encuesta a partir de datos del programa Proagro Productivo 2014, donde N= 29 828 y n= 379. Después de la colecta de información, se elaboró una base de datos en Excel, se codificó y procesó con el programa SPSS-16. Los resultados evidencian que el mayor gasto de energéticos fósiles en ambos grupos se da en la cosecha y es menor en labores culturales. Sin embargo, en este rubro el gasto de energía derivada de petróleo es dos veces mayor en el SMo. Además, el gasto de energéticos calculado y la emisión de CO2e son 30.8% mayor en el SMo versus el SMT para la misma proporción de maíz producido en cada sistema. Se concluyó que a pesar de que el SMT requiere mayor cantidad de mano de obra y fuerza de tracción animal, es más eficiente en el uso de energéticos de origen fósil y las emisiones de GEI calculados son menores.

Palabras clave: agricultura; eficiencia; energía; productividad


Maize is the world’s most widely grown cereal, production in 2014 was 982 million metric tons (tm) worldwide (USDA, 2014; IGC, 2015). In México, it is the grain that is most intended for human consumption and it is estimated that on average 343 g per day per capita (CEDRSSA, 2014) are consumed. Beans are a grain that globally has less importance than maize, according to the USDA, during 2014 were harvested about 16 million tm, but in México its importance for human consumption is higher, with an estimated of 11 kg per capita at year, although in rural areas and in lower income strata it increases to more than 13 kg (SE, 2012).

Maize in México was traditionally cultivated in association with some type of bean and squash, occasionally also associated with chili pepper and tomato among others. This type of polyculture is known as the traditional milpa system (SMT) and is considered as a viable alternative that combines ingenious peasant and indigenous practices and integrates products for diet diversification. In addition, the Food and Agriculture Organization (FAO) recognizes it as an Important System of World Agricultural Heritage (FAO, 2011). According to Hernández and Aguirre (1998), traditional agriculture is characterized by better use of local resources, is produced more for self-consumption and is low-entropy. Less polycultures are being sown, due to the application of the Green Revolution (RV) technological package, designed in México from the 40’s of the last century and implemented in the 60’s (Hewitt, 1985).

Currently, the main form of maize cultivation is monoculture (SMo) with some negative consequences for soils such as high erosion levels, fertility loss, aquifers contamination and in general to the environment; due to the intensive forms of agroindustrial production in the country. The technological RV package has fostered a great dependence on pesticides, seeds, machinery and equipment produced by large transnational corporations through techno-scientific systems (Álvarez-Buylla, 2013).

This hegemonic production model implies high costs of the technological package that are not accessible to peasants and indigenous people and use large amounts of fossil fuels in the production and application of agrochemicals, as well as in the manufacture and operation of agricultural machinery and equipment such as tractors, combine harvesters, balers, mowers, etc. Non-renewable fuel reserves are consumed, propitiating the production of biofuels from human food and generating large amounts of GHG which, according to the Intergovernmental Panel on Climate Change (IPCC), agriculture accounts for 14% of Global emissions of GHG, although if the manufacture of machinery, agrochemicals and their use are taking into account the proportion exceeds 30% of global emissions in the agricultural sector (Martínez and Fernández, 2008; Bermejo, 2010; IPCC, 2013).

Several authors like Altieri (1999); Altieri and Nichols (2000): Gliessman (2002); Pimentel and Pimentel (2005); Damian et al. (2013); among others, agree that modern agroecosystems have in recent years intensified the use of energy of fossil origin, that depend on two main energy flows: the natural one that corresponds to solar energy and an auxiliary flow controlled by the farmer through the use of fossil fuels, basically, either directly or indirectly. Fossil energy sources correspond to a type of “stored” energy, its existence is finite, relatively expensive and generally not environmentally friendly, because its use causes pollution through the emission of various harmful gases, CO2 among them for its GHG effects (Pimentel and Pimentel, 2005). The objective of this research was to know the efficiency of fossil energy use in SMT and SMo and the emission derived from GHG for the state of Tlaxcala, México.

Materials and methods

The state of Tlaxcala is located in the central Mexican plateau between 19° 44”-19° 06” north latitude and 97° 37”-98° 44” west longitude, at an average altitude of 2 230 m. It borders to the southwest, south, east and a north section with the state of Puebla; to the north and northwest with the state of Hidalgo and in a small strip of the northwest with the state of México. It is the smallest entity in the country; is divided into 60 municipalities, it has an area of 3 997 km2 and in 2010 there were 1 169 936 inhabitants, of which 20% were located in rural areas (INEGI, 2010). The climate is temperate sub-humid C(w) in 92% of the territory; the annual average temperature is 14.5 °C and the average annual rainfall is 720 mm with summer rains.

In order to obtain primary information, a mixed methodology was used through the survey and semi-structured interview. In the survey, data from the Federal Proagro Productive program of 2014 for Tlaxcala was used. The universe of beneficiaries producing maize was 29 828 (N) (Proagro Productivo, 2014). The sample size was calculated with maximum variance values; accuracy of 5%; value of the normal distribution of 1.96; probability of error of 5%; and 95% confidence level. The following formula was used.


Calculations were performed to determine the sample size n= 379 and an equal number of maize producers were chosen ramdomly for the application of the survey. With the collected data the producers were classified in two systems of interest for this paper, being as follows: 1) SMT nμ= 59; and 2) SMo nμ= 320. Twenty semi-structured interviews were also conducted with key informants to corroborate and supplement the survey information. Then captured and sorted in Excel for Windows, coded and analyzed in the Statistical Package for the Social Sciences (SPSS) version 16 program.

To obtain data on fuel consumption in each system, information was generated from producers in each group who used machinery and equipment for soil preparation, planting, till work and harvesting. Simultaneously owners of tractors and machines were interviewed to know how many liters of fuel they require for each job. These data were converted to Mega Joules (MJ) of energy used. The conversion was made depending on the type of energy used: in the case of diesel, the calculated liters were multiplied by 36.7 to convert to MJ; for gasoline, the conversion factor was 32 and for electricity 3.6 MJ kW-1 h-1. Subsequently, the partial data were added to meet the total consumption of fossil energy and then CO2e was calculated, first calculating the amount of CO2, CH4 and N2O generated by ignition of fossil fuel, then multiplied by 21 and 310 respectively data on CH4 and N2O to calculate CO2e and based on one hundred years. Finally this data was added to the calculated amount of CO2 (Pimentel and Dazhong, 1990). In order to calculate the total fossil energy, the following formula was used.


Where: efTotal= calculated total fossil energy; efprep= fossil energy used in soil preparation; efsowing= fossil energy used for sowing activities; eftilwor= fossil energy for tilling work (weeding, tillage, asegunda, fertilization and fumigation); efharvest= fossil energy used to harvest grain and grass.

At the same time, a formula was used to calculate the fuel used and the energy derived for each of the phases of the agricultural cycle per hectare.The following formula is used to calculate fossil fuels used in soil preparation.


Where: efprep= calculated fossil energy for soil preparation; nµ= Stratum size (applies to all partial formulas); barbecho= number of producers fallow (multiplied by 14.3 L ha-1); dredge= number of producers that track (multiplied by 8 L ha-1).

To calculate the energy used in activities related to planting, the following was applied.

efsowing=Furrowing with tractornμ+Seeding with tractornμ

Where: efsowing= fossil energy used for planting; Furrowing with tractor= number of producers that forrows with tractor (multiplied by 7 L ha-1); seeding with tractor= number of producers who sow with tractor (multiplied by 8 L ha-1).

The formula used to calculate energy used for tilling work is the following.


Where: eftilwor= fossil energy calculated for fertilization, cultivation and spraying; fertilization= number of producers who fertilized with tractor (multiplied by 3 L ha-1); escarda= number of producers weeding with tractor (multiplied by 7 L ha-1); labra= number of producers tilling with tractor (multiplied by 7 L ha-1); Asegunda= number of producers asegundan with tractor (multiplied by 7 L ha-1); fumigation= number of producers fumigating with tractor (multiplied by 3 L ha-1 or, if gasoline engine sprayer was used it was multiplied by 2 L ha-1).

Formula raised to calculate energy used for harvesting grain and dry grass.

eftharvest=Combinadanμ+Empacadoranμ+Desgran a gasolinanμ+Fletenμ+Desgran elecnμ

Where: efharvest= fossil energy used to transport and harvest grain and grass; combinada= number of producers harvesting with combined (multiplied by 35 L ha-1); empacadora= number of producers who packaged its dry grass (multiplied by 20 L ha-1); desgran a gasolina= producers using gasoline shelling machine (multiplied by 1.8 h ha-1 and by 2 L gasoline ha-1); flete = producers who transport their harvest (multiplied by 20 L of gasoline); desgran elec= producers using electric sheller (multiplied by 1.8 h ha-1 and 1.5 kW h-1).

In addition, the Student’s t-test for independent samples was applied to the values for the fuel quantity for each set of agricultural activities in the two systems (SMT and SMo). In this process, the Kolmogorov-Smirnova Normality test was first performed because the samples were larger than 30 units in each group with a value of α≤ 0.05. Once verified that the data of both groups behave within Normality, we proceeded to apply the test of equality of variance (Levené test) to later apply the bilateral significance test.

Results and discussion

Traditional milpa system (SMT)

The SMT is a polyculture that has different variants according to biophysical and cultural conditions. In the case of Tlaxcala, various types of associations were found in all of them, maize (Zea mays L.) with one or more of the following species and varieties: beans (Phaseolus vulgaris L.); ayocote (Phaseolus coccineus L.); broad bean (Vicia faba); and pumpkin (Cucurbita sp). The SMT is a result of the preservation of traditional Mesoamerican practices that, in this zone, receives different names like “milpa” or “Traditional Milpa System” (Sánchez and Castro, 2011; Sánchez and Hernández, 2014). The SMT ranked 20% of the total producers surveyed (59 people); however, only 5% are peasants who were found at random, the rest were placed in a targeted manner, due to the low proportion of peasants still planting milpa.

The age of the producers of this group varies from 35 to 86 years (with average and median of 58 years), they possess on average 3.7 ha, although the range fluctuates between 0.5 and 9 ha. The group of respondents is made up of 14% women and the rest are men. In general, average schooling is almost five years, and 6.8% of the total do not know how to read or write. In addition, 28% of producers have another job for the generation of complementary income, and the average number of members per family is five, although 57% of families are made up of two to four people and the rest are made up of five to 11.

Soil preparation

According to the collected information, in order to prepare the soil before sowing, fallow and dredge are basically carried out, depending on the economic conditions of the producers. Occasionally dredge is not carried out, due to its high costs and soil is only traced; in other cases, up to two dredges and three or four pre-sowing trawls are carried out when the producer has his own tractor. For dredging the rental cost of tractor varies between $600.00 and $1 200.00 ha-1, and for harrow $400.00 to $1 200.00 ha-1 varying on every State region. The proportion of producers that dredge with tractor is 57.6%, while 76.4% harrows once and 8.3% twice. To calculate the amount of fuel used in the soil preparation, a factor of 36.7 was used to convert the liters of diesel (Ld) to MJ.

efprepSMT=3414.3Ld ha-159+458Ld ha-159=14.34Ld ha-136.7=526.3MJ ha-1


Here two possibilities were placed in the use of tractor: through the furrow (to later plant using shovel, a tapapié or a yunta planter) and planting with tractor equipment. In the SMT 40.7% of producers use tractor for furrowing; 45.7% planted with yunta seeder and 13.6% used tractor seeder. By replacing the data in the formula the following results were obtained.

efsiembraSMT=247Ldha-159+88Ldha-159=3.94Ld ha-136.7=144.6MJ ha-1

Tillage work

In this area the fertilization, weeding, tillage, asegunda and fumigation were considered. In the SMT only four producers fertilize with tractor at the time of sowing. In addition, 11.9% of peasants weed, 8.5% worked the soil and 15.3% asegundan with tractor; the rest use yunta and some do not perform these tasks. Finally, 11.9% apply some insecticide; however, only 3.4% use gasoline engine sprinkler and the rest, manual backpack. To convert the liters of gasoline (Lg) to MJ, it was calculated with a factor of 32.

eftilworSMT=77Ld ha-159+57Ld ha-159+97Ld ha-159+22Lg ha-159=(2.49Ld ha-1)36.7+0.07Lg ha-132=93.62MJ ha-1


In the SMT, the proportion of producers that use combined is 6.8% and 94.9% grind or threshes their grass, for the purpose of selling or saving it for their livestock. In these activities the fuel used was diesel. The proportion of peasants that threshed with gasoline machines was 28.8% and 83% used freight. Finally, producers using electric motor thresher represent 8.5%. The calculated energy is shown below.

efharvestSMT=435Ld ha-159+5620Ld ha-159+173.6Ld ha-159+4920Lg ha-159+51.8h ha-11.5kW h-159=(2.37+19LDha-1)36.7+ 1.04+16.61Lg ha-132+ 0.23kWha-136.7MJ = 1349.9MJ ha-1

With these results the total energy used per hectare in the STM was calculated, being as follows.

efTotalSMT=526.MJ ha-1+144.6MJ ha-1+93.62MJ ha-1+1349.9MJ ha-1=2114.42MJ ha-1

The results show that 2 114.42 MJ ha-1 are used, corresponding to 57.62 liters of diesel equivalent (Lde) per hectare among members of the SMT. Harvested dry biomass (BSC) was calculated by adding the yield per hectare of maize, bean and pumpkin seed, dry maize grass, bean and pumpkin thatch. Maize yield was 978 kg ha-1 and 140 pieces of bales per hectare (21 354 kg each). The average BSC was 5 638 kg ha-1, and 29.13 Lde are used to produce a tm of maize. With these data direct emissions were calculated, and the result for the SMT was 163.3 kg of CO2e ha-1.

Maize monoculture system (SMo)

In the SMo only maize is sown. In this way, the crop conditions for the mechanization in terms of planting, tillage tasks, irrigation, herbicides application and harvest are adapted.This type of cultivation is a result of the RV technological package. 80% of the sampled producers belong to this group in the state of Tlaxcala (320 people), ranging in age from 23 to 93 years and an average of 62 years. The amount of land they cultivate is 5.5 ha on average, however, the range fluctuates between 0.5 and 60 ha. Of the people surveyed, 15% are women; the illiteracy level is 6.2% and each family has five members on average. The practices carried out are mentioned below.

Preparation of soil

The proportion of peasants who plough using a tractor is 85.3%, and 6.9% do not plough prior to planting due to the high costs involved. In the case of the dredge, when these activities are carried out using animals, the peasants call it “contlapanear”; occasionally it is carried out at the time of harvest and then before planting, even, a biga is passed over to undo the lumps and seal the soil so that it does not lose much moisture. In this group 8.8% uses a yunta and 90.9% use tractor for this purpose. Below is the calculation of fuel and energy used.

efprepSMo=27314.3Ld ha-1320+2918Ld ha-1320=19.5Ld ha-136.7=715.65MJ ha-1


In the SMo, 29.7% furrows with tractor and 12.8% with yunta; the rest (57.5%) does not furrow previously, precisely because they sow with tractor equipment. In addition, 18.4% do so with sowing machine pulled by yunta; 23.1% sows using shovel and 1% sows to tapapié. The fuels use is as follows.

efsiembraSMo=957Ld ha-1320+1848Ld ha-1320=6.72Ld ha-136.7=246.63MJ ha-1

Tillage work

In this group 10% of producers fertilize maize with a tractor; 83.4% do it manually and the rest does not fertilize. Regarding weeding, 38.1% performed it with tractor, 20.9% tillage and 33.4% asegunda with machinery; the rest does it with yunta or does not carry out these tillage works. In addition, 67.5% used herbicides and 12.8% apply some insecticide; however, most of them do it with a manual backpack, 8.4% apply it with a backpack and 4% do so with a tractor. The calculations are as follows.

eftilworSMO=323Ld ha-1320+1227Ld ha-1320+677Lg ha-1320+=1077Lg ha-1320+133 Ld ha-1320+272 Lg ha-1320= 6.93Ld ha-136.7+ 0.17Lg ha-132= 259.33MJha-1


For the harvest, in this group the mechanization is more feasible than in the SMT. The proportion of producers using a combined machine to harvest their maize is 13.4% and the rest do it manually and the grass is packed by 89.1% of peasants. In addition, producers using gasoline engine grinders represent 62.8%, with a 12.5% electric motor and 77% used freight to move their harvest. The energy calculated for the harvest in this group is shown below.

efharvestSMo=4335Ld ha-1320+28520 Ld ha-1320+2013.6Ld ha-1320+24620Lg ha-1320+401.8 h ha-11.5k W ha-1320= 22.5 Ld ha-136.7+ 17.7Lg ha-132+(108 kW ha-1)(3.6 MJ) = 1780.95 MJha-1

The concentration of the above parameters allowed to calculate the total energy used per hectare in the system of maize production in monoculture, being as follows.


SMO uses about 81.8 Lde ha-1; for calculating the average BSC performance, the average maize yield 1 942.8 kg ha-1 and 142 bales ha-1 were contemplated. The average BSC was 4 975 kg ha-1 and for this group 41.35 L of diesel are used per ton of maize grain. Regarding the calculation of direct emissions of CO2e, the results were 231.9 kg of CO2e ha-1.

Fossil energy use and CO 2 e production of compared cultivation systems

Student’s t-Test was applied to data related to the use of fossil fuels (and consequent generation of CO2e) from agricultural activity, the results for soil preparation were F= 6.464, p= 0.116, this situation indicates that there is no significant difference between the groups (SMT and SMo). For sowing cases (F= 223, 615, p= 0.001) and tillage tasks (F= 34 928, p= 0.002) there is a highly significant difference which shows that SMo uses more fuel and generates more CO2e than the SMT in these activities (Doménech et al., 2012; Guevara, 2013). However, the task that used more fuel was harvesting, where F= 3.068, p= 0.255, no significant difference exists (Table 1).

Table 1 Comparison of energy use and emissions of CO2e between production systems. 

Fuente: elaboración con datos de campo febrero-mayo 2015. nμSMT= 59; nμSMo= 320; ns= no significativo; **= altamente significativo.

Material and energy balances are important to know if there is a high or low efficiency in a system. According to Odum (1983), agricultural systems are open and dissipative, a situation that involves energy use for growing, maintaining and establishing a flow of matter and energy in its environment. This paper shows the results of SMT that employs 2 114.4 MJ ha-1 equivalent to 57.6 Lde ha-1 of efTotal and produces 82.6 kg of CO2e tm-1 of maize grain. The SMo used 3 002.6 MJ ha-1 corresponding to 81.8 Lde ha-1 that generates 119.4 kg of CO2e tm-1 of maize.

Guevara et al. (2013); Reyes-Muro et al.(2013) reported on a paper carried out in Frailesca Chiapas region, that for that maize area whose average yields were 3.47 tm ha-1 producers used 1 788.2 MJ tm-1 of maize approximately. However, the direct use of fuel (for tractor) represents 6% of the total, which involves the use of 108 MJ tm-1.The situation is that in that region 85.7% of producers use “improved” seeds that generate relatively high yields and only 11% use soil preparation machinery; the rest do the work manually. In this case, most of energy used for production systems is biological (human and yoke), which is why they emit only 8.1 kg of CO2e tm-1.

While in a research with different crops in La Rioja, Spain, the most similar for the point of comparison with maize are wheat and barley; according to Domenech et al. (2012) agricultural activities generate 1.42 tm of CO2e ha-1 for the concept of direct emissions; the sum of direct and indirect emissions exceeds 2 tm CO2e ha-1 for those crops.

In both cases, the results of reported CO2e emissions are extreme. While in Guevara et al. (2013) paper direct use emissions represent 6%, Doménech et al. (2012) report is 11 times higher (67%) in relation to the same concept. However, in the first one the crop is maize and in the second are barley and wheat. In addition, the context is very different between them, since the case of Chiapas is carried out in conditions of a high use of labor for maize cultivation, and in the case of La Rioja apparently it is of intensive use of machinery and equipment in barley and wheat crops.

Other references are Wayne (1990) and Pimentel and Pimentel (2005), which assert that in the United States of America 142.5 L of diesel are used for each tm of maize grain produced.This amounts to 7 425.8 MJ tm-1 maize, generating 437 kg of CO2e tm-1, which are higher values than those obtained in this paper. According to SIAP (2015), for 2014 in the state of Tlaxcala 115 603 ha of maize were sown and 114 453 ha were harvested with an average yield of 3.18 tm ha-1. The total amount of grain produced at state level was 364 450 tm during that year, considering rain-fed and irrigation conditions.

If all Tlaxcala maize had been produced in conditions of fossil energy use similar to that used in the United States of America in 2014, it would have been 2 706 332 810 MJ or 2 706 333 TJ of energy and 151 631 tm of CO2e would have been generated. But if all the tlaxcalteca maize production had been under similar conditions to SMT on the use of fossil fuels, the energy used must have been 389 582.5 TJ and 30 103.6 tm of CO2e would have been emited. However, making a calculation close to reality of how it occurred, and considering that only 5% of producers planted in SMT and 95% in SMo, the energy used was approximately 554 577.2 TJ and generated around 42 844.7 tm of CO2e.


Maize is a grass that has been domesticated in México for about nine thousand years and has been cultivated associated with various species such as beans, squash and chili peppers among others. In the state of Tlaxcala, the SMT is now almost extinct, since only five out of 100 maize farmers sow it associated with some legume. The use of fuels derived from petroleum is greater in the SMo, although there is only statistical difference in the areas of planting and tillage tasks. However, in soil preparation and harvesting the difference in fossil fuel use would be significant when it is taking into account that the SMT also harvests beans, broad beans, ayocote and occasionally pumpkin seed. However, in this paper the comparison was not performed considering its equivalences.Similarly, the CO2e emission is proportionally lower in the SMT than in SMo.Generally speaking, from a perspective of the use of fossil energy and GHG emissions, the SMT is more efficient, it also has positive implications for the agroecosystem, bringing benefits to the farmers’ economy as well as food diversity.

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Received: January 2017; Accepted: March 2017

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