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

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 CH₄in 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.