Greenhouse gas emissions from a chinampa soil or floating gardens in Mexico

 

Emisión de gases de efecto invernadero de un suelo de chinampa o jardines flotantes en México

 

Nadia Livia Ortiz-Cornejo¹, Marco Luna-Guido², Yadira Rivera-Espinoza¹, María Soledad Vásquez-Murrieta¹*, Víctor Manuel Ruíz-Valdiviezo³ and Luc Dendooven²

 

¹ Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Prolongación de Carpió y Plan de Ayala S/N, México, D.F., México, C.P. 11340 *Corresponding author: murrieta@hotmail.com

² Laboratorio de Ecología del Suelo, Centro de Investigación y de Estudios Avanzados, Instituto Politécnico Nacional. Avenida Instituto Politécnico Nacional 2508, México D.F., México, C.P. 07360

³ Laboratorio de Biotecnología, Instituto Tecnológico de Tuxtla Gutiérrez, Carretera Panamericana km 1080, Colonia Juan Crispin, Tuxtla-Gutiérrez, Chiapas, México, C. P. 29050

 

Received January 2015;
accepted April 2015

 

Abstract

Agriculture in chinampas or 'floating gardens', is still found on the south of Mexico City, it is a high yield pre-Columbian cultivation system, which has soils enriched with organic matter. The objective of this research was to determine the greenhouse gas (GHG) emissions from a chinampa soil cultivated with amaranth (Amaranthus hypochondriacus L.), maize (Zea mays L.) or uncultivated. The soil was characterized and fluxes of GHG (CO₂, N₂O and CH₄) were monitored for one year. The chinampa soil was alkaline saline with an organic C content that ranged from 21.7 t/ha in the 0-20 cm layer of the soil cultivated with amaranth to 28.4 t/ha in the 20-40 cm layer of the uncultivated soil. The cumulative GHG emissions (kg CO₂-equivalents/ha/y) were 395, 376 and 258 for N₂O, and 44, 30 and 26 for CH₄ in the uncultivated, amaranth cultivated and maize cultivated soil, respectively. No significant effect of cultivated crop or soil characteristics on GHG emissions over one year was found. In general, N₂O contributed 91 % and CH₄ 9 % to the global warming potential of the GHG. The organic C was high and distributed equally over the soil profile, because it is an anthropic soil.

Key words: GHG, fluxes of carbon dioxide, methane and nitrous oxide, global warming potential, C sequestration.

 

Resumen

La agricultura en chinampas o "jardines flotantes", todavía la podemos encontrar al sur de la Ciudad de México, este es un sistema de cultivo de alto rendimiento pre-colombino con suelos ricos en materia orgánica. El objetivo de esta investigación fue determinar la emisión de gases de efecto invernadero (GEI) del suelo de chinampas cultivadas con amaranto (Amaranthus hypochondriacus L.), maíz (Zea mays L.) y sin cultivo. Se caracterizó el suelo y se monitorearon los flujos de gases de efecto invernadero (CO₂, N₂O y CH₄) durante un año. El suelo de la chinampa fue salino alcalino con un contenido de C orgánico que varió de 21.7 t/ha en la capa de 0-20 cm del suelo cultivado con amaranto a 28.4 t/ha en la capa de 20-40 cm del suelo sin cultivar. Las emisiones de gases de efecto invernadero acumuladas (kg de CO₂ equivalente/ha/año) fueron 395, 376 y 258 para el N₂O y 44, 30 y 26 para el CH₄, en el suelo sin cultivo, en el cultivado con amaranto y en el cultivado con maíz, respectivamente. No se encontró un efecto significativo del cultivo o de las características del suelo sobre las emisiones de gases de efecto invernadero durante un año. En general, el N₂O aportó el 91 % y el CH₄ aportó el 9 % del potencial de calentamiento global de los GEI. El C orgánico fue elevado y se distribuye por igual en el perfil del suelo, debido a que es un suelo antrópico.

Palabras clave: GEI, flujos de dióxido de carbono, metano y óxido nitroso, potencial de calentamiento global, secuestro de carbono.

 

INTRODUCTION

In Mexico, Xochimilco's chinampas are also known as floating gardens, they are high yield agricultural systems since pre-Columbian times. They are a system of small plots (500-1000 m²) surrounded by channels (Morehart and Frederick 2014). Swamps were reclaimed by digging channels by hand, creating small plots, chinampas are typically narrow, around 4 m wide, but may extend in length up to 400-900 m (Arco and Abrams 2006). Lake sediment was added constantly to the gardens and trees were planted at the borders to strengthen them and to protect the banks from erosion (Leszczynska-Borys and Borys 2010, Morehart 2012). An intensive agricultural system that provided food to Tenochtitlan the whole year was created. Currently, flowers, maize (Zea mays L.), vegetables and amaranth (Amaranthus hypochondriacus L.) are still cultivated there in a more or less traditional way, although more and more modern techniques with extensive use of inorganic fertilizers, pesticides and herbicides prevail (Clauzel 2009).

The main contribution to anthropic GHG emissions after the burning of fossil fuels is from agricultural soils. Agriculture contributes up to 30 % of the anthropic GHG emissions that drive climate change (Smith and Gregory 2013). Agricultural activities are responsible for approximately 50 % of the global atmospheric CH₄ emissions and agricultural soils for 75 % of the global N₂O (Wang et al. 2012). Management practices, such as irrigation, tillage, cropping system, and N fertilization, can alter soil GHG emissions substantially. The GHG are produced as a result of some microbial processes in the soil, but the flux between soil and the atmosphere depends largely on physical factors and soil conditions (Sanford et al. 2012).

If the GHG emission occurs in conventional agricultural soils, then it would be expected higher emission from a chinampa soil due to the content of organic matter and humidity that could affect the GHG emission. However, no information exists about how chinampas contribute to global GHG emissions, so the objectives of this research were to characterize a chinampas soil, to monitor the GHG fluxes (CO₂, CH₄ and N₂O) for one year from an uncultivated soil and two cultivated soils with maize and amaranth (these two plants were used due to their food and farm importance in the chinampas zone), and also to calculate the global warming potential (GWP) emitted from these systems.

 

MATERIAL AND METHODS

Experimental site

The experimental site is located to the south of Mexico City in Xochimilco (19° 16' 27.05'' N, 99° 05' 33'' W) at an altitude of 2240 masl. The climate is temperate with precipitation 600-1000 mm/year mostly from June to October. Mean annual temperature is 16 ^oC. The soils of the chinampas are of anthropic origin.

Recently, the remaining chinampas are fertilized with low-grade sewage and many of the channels have become stagnant and contaminated with garbage and domestic waste runoff. Increasingly, insecticides and chemical fertilizers are being used to cultivate new and "improved" plant varieties (Chapin 1988).

Experimental design

Three plots (6.5 x 28 m) covered mostly with grasses were cultivated with maize, amaranth or left fallow to monitor GHG. A systematic sampling was performed similarly in each plot. Maize and amaranth were planted on beds 40 cm wide with a 60 cm spacing between the rows on July 8^th 2012 and then harvested in January 2013. The crops were unfertilized and no herbicides or pesticides were applied. Weeds were removed when required and during the dry season, from September 2012 to January 2013 (harvest), once a week, 1.2 L of water from the channel was used to irrigate each plant. The plots with grass were left undisturbed and served as control.

Greenhouse gas emissions

CO₂, CH₄ and N₂O fluxes were monitored simultaneously from February 1^st 2012 to January 28^th 2013. Three chambers (25 cm length x 20 cm, internal diameter) were placed in the three plots of each treatment. They were designed as reported by Parkin et al. (2003) with a coated top and a sampling port fitted with a butyl rubber stopper. The chambers were inserted 5 cm into the soil. Gas sampling was done between 10:00 and 12:00 h. The covers were placed on the chambers and sealed airtight with Teflon tape. A 15 cm³ air sample was collected from the PVC chamber at 0, 20, 40 and 60 min after it was closed. The gas in the headspace was mixed by lushing 5 times with the air inside the chamber followed by gas collection for analysis. The 15 cm³ air sample was injected into 15 cm³ evacuated vials closed with a butyl rubber stopper and sealed with an aluminium cap pending analysis.

The headspace of the vials was analyzed for CO₂, CH₄ and N₂O on two Agilent Technologies 4890D gas chromatographs (GC) according to Serrano-Silva et al. (2011).

Soil characterization

Each plot used to measure GHG fluxes was sampled by drilling 20 times the 0-20 cm layer. The soil samples from each plot were pooled (n = 9), sieved separately and characterized. The features measured to the soils were: pH, electrolytic conductivity (EC), water holding capacity (WHC), total N, organic C and soil texture, as described by Serrano-Silva et al. (2011).

Additionally, at the onset (February 2012) and end (January 2013) of the GHG monitoring, soil samples were taken from the 0-20, 20-40 and 40-60 cm layers in each plot to determine the total carbon (C_tot) and bulk density. Calculation of the net GWP was based on Robertson et al. (2000) and Thelen et al. (2010), taking into account soil C sequestration (Δ soil C GWP), emissions of GHG from the soil (soil N₂O flux + soil CH₄ flux), emissions of GHG from the fuel used for farming operations (which in this case were not used) (operation GHG flux) and the production of fertilizer and seeds (input GHG flux, were not used). The net GWP was calculated as:

Net GWP = Δ soil C GWP + soil N₂O flux + soil CH₄ flux + operation GHG flux + input GHG flux.

The overall GWP of the gasses emitted was calculated considering the GWP of 298 and 25 CO₂-equivalents for N₂O and CH₄, respectively (IPCC 2007).

Statistical analysis

Emissions of CO₂, CH₄ and N₂O were regressed on elapsed time, i.e. 0, 20, 40 and 60 min, using a linear model forced to pass through the origin, but allowing different slopes (production rates). The sample at time 0 accounted for the atmospheric CO₂, CH₄ and N₂O, and was subtracted from the measured values.

The C content in the 0-20, 20-40, 40-60 and 0-60 cm layers were subjected to a two-way analysis of variance using Proc GLM (SAS 1989) to test for a significant effect from layer, treatment and their interaction. Significant differences between treatments for CO₂, CH₄ and N₂O emission rates were determined using Proc Mixed considering repeated measurements (SAS 1989).

The total CO₂, N₂O and CH₄ emissions over the one-year period were calculated by linear interpolation of data points between each successive sampling event (Ussiri et al. 2009) and numerical integration of underlying area using the trapezoid rule (Whittaker and Robinson 1967).

RESULTS

Soil characteristics

The pH of the sandy clay loam soil was alkaline and EC ranged from 2.79 to 6.64 dS/m (Table I). The WHC of the soil ranged from 1888 to 2190 g/kg and total N from 5.92 to 6.17 g/kg, while the C_tot was considered high and ranged from 45.8 to 48.6 g/kg soil. None of the soil characteristics was significantly different between treatments.

Greenhouse gas emissions

The CO₂ emission did not show a clear pattern, but was higher by the end of 2012, and in the beginning of 2013 it ranged from 0.0012 to 6.0306 kg/ha/d (Fig. 1a). The emission of N₂O was considered low and ranged from -0.0065 to 0.0118 kg/ha/d (Fig. 1b). Sometimes negative values were obtained, i.e. reduction of N₂O was larger than its production. The emission of N₂O did not show large changes over time. The emission of CH₄ was low without a clear pattern (Fig. 1c). The flux of CH₄ ranged from -0.0249 to 0.0259 kg/ha/d and was mostly positive, so production prevailed over oxidation. The CO₂, N₂O and CH₄ emission rate was not affected significantly by treatment (Table II).

Global warming potential of the greenhouse gasses The GWP of N₂O and that of CH₄ were similar in the different treatments and varied between 258 and 395, and between 26 and 44 kg CO₂-equivalents/ha/y, respectively (Table III). Consequently the GWP of the GHG was similar in the different treatments.

C content in the soil profile

The organic C content of the soils ranged from 21.7 t/ha in the 0-20 cm layer of soil cultivated with amaranth to 28.4 t/ha in the 20-40 cm layer of uncultivated soil (Table IV). Soil layer, treatment and their interaction had no significant effect on the soil C content.

 

DISCUSSION

Soil characteristics

Adverse effects of salinity and alkalinity on plants have been reported (Carrion et al. 2012). The high EC and pH found in the chinampas soil might inhibit growth of certain crops. The chinampas soil has a high organic matter content compared to arable soils of the regions, e.g. 7.2 g C/kg found in soil of Otumba (State of Mexico). Soils with high organic matter content do generally have a good fertility, and crop yields are high (Ball et al. 2007).

The constant application of sediment buries the organic material in the deeper soil layers. Consequently, the soil profile was organic rich, but with no clear gradient as normally found in arable soils (Table IV). The values found for C_tot in the 0-60 cm layer ranged from 73.9 in the maize cultivated soil to 81.7 t C/ha in the uncultivated soil, similar values have been reported in agricultural soils in the region. In the 0-60 cm layer of a conventional tilled soil with wheat and maize crop rotation and removal of residue in the valley of Mexico, the carbon content was 69.7 t C/ha (Dendooven et al. 2012).

Greenhouse gas emissions

Emissions of CO₂ were generally low in the first half of the year, but tended to increase towards the end of the year (Fig. 1a). During the dry season, i.e. mostly from November to May, channel water is used to irrigate the crops. The channel water is organic rich (Chavarría et al. 2010) and the mineralization of the applied organic material will increase CO₂ emissions.

Mineralization of the organic matter will provide nutrients for the crops, but this will also favour N₂O emissions, especially when an excess of mineralized N is present (Towprayoon et al. 2005). Additionally, frequent application of channel water will increase emissions of N₂O as the moisture content increases and denitrification is stimulated (Stewart et al. 2012). Cultivation of crops is also known to increase the emission of N₂O, as root exudates mineralization might stimulate denitrification (Kettunen et al. 2007).

In this study, N₂O emissions were generally low and occasionally even negative (Fig. 1b). Stewart et al. (2012) suggested that N₂O uptake can occur at relatively low soil moisture and temperature, and limited soil N. These conditions might be present in the chinampa soil, especially during dry spells in the rainy season.

In the chinampa soil, the CH₄ flux was mostly positive so the production of CH₄ was often larger than its oxidation. The high organic matter content (which stimulates microbial activity and oxygen consumption) and the regular irrigation with channel water, facilitate the creation of anaerobic microsites, and in consequence, methanogenesis.

CO₂, N₂O and CH₄ fluxes were not affected by crop. Management practices, such as irrigation, tillage and cropping system, as well as characteristics of the soils were similar in the study, so their effect on GHG emissions would be the same in the three treatments. The only different factor between treatments was the cultivated crop. It has to be considered, however, that crops-vegetables-lowers are regularly rotated in chinampa so it is very unlikely that crop will have an effect on GHG emissions.

Global warming potential of the greenhouse gases

N₂O contributed 91 % to the GWP of the GHG and CH₄ 9 %. N₂O is often the most important GHG from agricultural systems (Wan et al. 2012). It is only in rice-cultivation that CH₄ emissions are often more important than N₂O emissions (Horwath 2011). Cultivation of maize or amaranth had no significant effect on the GWP of the GHG. From this study, it can be assumed that the crop will have little effect on the GWP of the GHG emissions.

The GWP of the GHG was approximately 400 kg CO₂-equivalents/ha/y in a conventional agricultural system (tillage, maize monoculture, residue removal) in the valley of Mexico City in the year 2008-2009 and 230 kg CO₂-equivalents/ha/y in 2009-2010 (Dendooven et al. 2012). The values reported in this study were similar to those found in the arable soil mentioned above.

 

CONCLUSIONS

It was found that chinampa soils are saline-alkaline, rich in nutrients and organic matter as a result of application of lake sediment and plant residues.

N₂O contributed 91 % and CH₄ 9 % to the GWP of the GHG.

The GHG emissions were not affected significantly by cultivated crop or soil characteristics.

The organic C was equally distributed in the soil profile and large amounts of C were sequestered from the atmosphere.

 

ACKNOWLEDGMENTS

We thank the friendly collaboration of the family Medina, owners of the chinampa where the study was carried out, and CIBAC-UAM Xochimilco for its help in this work. The research was funded by CINVESTAV (Mexico), SIP-IPN 20090076 and 20120068, CONA-CyT project 98042. N.L.O-C, received grant-aided support from the 'Consejo Nacional de Ciencia y Tecnología' (CONACyT) and BEIFI-IPN. M.S.V.-M. and Y. R-E received grant-aided support of SNI-CONACyT and COFAA and EDI-IPN.

 

REFERENCES

Arco L.J. and Abrams E.M. (2006). An essay on energetics: the construction of the Aztec chinampa system. Antiquity 80, 906-918.         [ Links ]

Ball B.C., Watson C.A. and Baddeley J.A. (2007). Soil physical fertility, soil structure and rooting conditions after ploughing organically managed grass/clover swards. Soil Use Manage. 23, 20-27.         [ Links ]

Carrión C., Ponce-De León C., Cram S., Sommer I., Hernández M. and Vanegas C. (2012). Potential use of water hyacinth (Eichhornia crassipes) in Xochimilco for metal phytoremediation. Agrociencia 46, 609-620.         [ Links ]

Chapin M. (1988). The seduction of models: Chinampa agriculture in Mexico. Grassroots Dev. 12, 8-17.         [ Links ]

Chavarría A., González M.C., Dantán E. and Cifuentes J. (2010). Evaluación espacial y temporal de la diversidad de los ascomicetes dulceacuícolas del canal turístico Santa Cruz, Xochimilco, México. R. Mex. Biodivers. 81, 733-744.         [ Links ]

Clauzel C. (2009). Between urban pressure and heritage: Which place for agriculture in the Chinampas of Xochimilco (Mexico)?. Cah. Agric. 18, 323-328.         [ Links ]

Dendooven L., Patiño-Zúñiga L., Verhulst N., Luna-Guido M., Marsch R. and Govaerts B. (2012). Global warming potential of agricultural systems with contrasting tillage and residue management in the central highlands of Mexico. Agric. Ecosyst. Environ. 152, 50-58.         [ Links ]

Horwath W.R. (2011). Greenhouse gas emissions from rice cropping systems. In: Understanding greenhouse gas emissions from agricultural management (L. Guo, A.S. Gunasekara and L.L. Mcconnell, Eds.) ACS Symposium Series 1072, American Chemical Society-Oxford University Press Inc., Washington, D.C., USA, pp. 67-89.         [ Links ]

IPCC (2007). The physical science basis. Summary for Policymakers. Intergovernmental Panel on Climate Change WGI, Fourth Assessment Report, Climate Change. Geneva, Switzerland. [On line]. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_sp.pdf.         [ Links ]

Kettunen R., Saarnio S., Martikainen P.J. and Silvola J. (2007). Can a mixed stand of N₂-fixing and non-fixing plants restrict N₂O emissions with increasing CO₂ concentration?. Soil Biol. Biochem. 39, 2538-2546.         [ Links ]

Leszczynska-Borys H. and Borys M.W. (2010). Splendor of Mexican prehispanic gardens. II International conference on landscape and urban horticulture. Acta Hortic. 881, 891-898.         [ Links ]

Morehart C. T. (2012). Mapping ancient chinampa landscapes in the Basin of Mexico: a remote sensing and GIS approach. J. Archaeol. Sci. 39, 2541-2551.         [ Links ]

Morehart C.T. and Frederick C. (2014). The chronology and collapse of pre-Aztec raised field (chinampa) agriculture in the northern Basin of Mexico. Antiquity 88, 531-548.         [ Links ]

Parkin T., Mosier A., Smith J., Venterea R., Johnson J., Reicosky D., Doyle G., Mccarty G. and Baker J. (2003). Chamber-based trace gas flux measurement protocol, USDA-ARS GRACEnet. USDA, pp. 1-28 [online] http://www.usmarc.usda.gov/SP2UserFiles/person/31831/2003GRACEnetTraceGasProtocol.pdf.         [ Links ]

Robertson G.P. and Paul E.A., Harwood R.R. (2000). Greenhouse gases in intensive agriculture: contributions of individual gases to the radiative forcing of the atmosphere. Science 289, 1922-1925.         [ Links ]

Sanford R.A., Wagner D.D., Wu Q., Chee-Sanford J.C., Thomas S.H., Cruz-García C., Rodríguez G., Massol-Deyá A., Kishore K.K., Kirsti M.R., Konstantinos T.K and Lofflerg F.E. (2012). Unexpected non denitrifier nitrous oxide reductase gene diversity and abundance in soils. Proc. Nat. Acad. Sci. USA 27, 19709-19714.         [ Links ]

SAS (1989). Statistic guide for personal computers. Version 6.04. (Ed.). SAS Institute, Inc., Cary. NC, USA.         [ Links ]

Serrano-Silva N., Luna-Guido M., Luqueño-Fernández F., Ceballos J.M., Marsch R. and Dendooven L. (2011). Dynamics of carbon and nitrogen and the emission of greenhouse gases in an agricultural soil amended with urea: a laboratory study. Appl. Soil Ecol. 47, 92-97.         [ Links ]

Smith P. and Gregory P.J. (2013). Climate change and sustainable food production. J. Proc. Nutr. Soc. 72, 21-28.         [ Links ]

Stewart K.J., Brummell M.E., Farrell R.E. and Siciliano S.D. (2012). N₂O flux from plant-soil systems in polar deserts switch between sources and sinks under different light conditions. Soil Biol. Biochem. 48, 69-77.         [ Links ]

Thelen K.D., Fronning B.E., Kravchenko A., Min D.H. and Robertson G.P. (2010). Integrating livestock manure with a corn-soybean bioenergy cropping system improves short-term carbon sequestration rates and net global warming potential. Biomass Bioenerg. 34, 960-966.         [ Links ]

Towprayoon S., Smakgahn K. and Poonkaew S. (2005). Mitigation of methane and nitrous oxide emissions from drained irrigated rice fields. Chemosphere 59, 1547-1556.         [ Links ]

Ussiri D.A.N., Lal R. and Jarecki M.K. (2009). Nitrous oxide and methane emissions from long-term tillage under a continuous corn cropping system in Ohio. Soil Till. Res. 104, 247-255.         [ Links ]

Wan S., Ward T. L. and Altosaar I. (2012). Strategy and tactics of disarming GHG at the source: N₂O reductase crops. Trends Biotechnol. 30, 410-425.         [ Links ]

Wang J., Zhang X., Liu Y., Pan X., Liu P., Chen Z., Huang T. and Xiong Z. (2012). Modelling impacts of alternative practices on net global warming potential and greenhouse gas intensity from rice-wheat annual rotation in China. PLoS One 7, e45668.         [ Links ]

Whittaker E.T. and Robinson G. (1967). Trapezoidal and parabolic rules. In: The calculus observations: A treatise on numerical mathematics. 4th ed. Dover, New York, EUA. pp 156-158.         [ Links ]