Effects of subsistence farming system on soil surface CO2–C flux on Cofre de Perote volcano slopes, Veracruz (Mexico)

Mountainous parts of the eastern slope of the Mexican Cofre de Perote volcano have suffered great ecological disturbance due to the conversion of forest to subsistence corn (Zea mays) cropland. This research was conducted in order to evaluate the response of surface soil CO2–C flux to land use modification, specifically the adoption of subsistence farming in this mountainous forest–cropland setting. The treatments consisted of a corn plot (CP), recently abandoned cropland (RA), old abandoned cropland (OA), and coniferous (Pinus species) forestland (CF). For an 8-month period (August 1999–June 2000), CO2–C flux concentration was measured monthly using the static chamber method. CO2–C flux ranged from 1.80 to 5.22 g C m^-2/day in the CF treatment, 2.76–8.45 g C m^2/day in the CP treatment, 3.24–7.48 g C m^-2/day in the RA treatment, to 2.99–8.84 g C m^-2/day in the OA treatment. Results showed that the conversion of coniferous forest to corn cropland leads to a significant increase in CO2–C flux concentration from the soil surface to the atmosphere. There were few differences between current and former agricultural plots, demonstrating that crop abandonment did not lower CO2–C flux from the soilʹs surface. Soil temperature and moisture content were poorly correlated with CO2–C flux; however, soil moisture data did show greater scattering. This indicates that soil temperature had a major effect on CO2–C flux concentration. To offset some of the organic carbon depletion from soil caused by land use change, it is recommended that the subsistence farming system subject corn crop residue to a composting process. This can improve short-term soil fertility and increase corn crop yield, playing a central role in converting abandoned cropland into permanent cultures that facilitate forest conservation.