CO₂ emission affected by moisture content and aggregate sizes in a calcareous soil of Comarca Lagunera, Mexico

ABSTRACT

Soil CO₂ emissions are formed from biotic and abiotic processes related to organic carbon (SOC) and inorganic carbon (SIC), respectively. Calcareous soil has a high amount of SIC and occurs mainly in arid areas, and little is known about CO₂ emissions from aggregates of this soil. This study aims to evaluate the emission of CO₂ of aggregates from calcareous soil in the Comarca Lagunera, Mexico. Soil samples were taken from the layers of 0.00-0.15 and 0.15-0.30 m, and soil physical and chemical properties were determined. Aggregates distribution was obtained using the dry-sieving method. Macro (0.25–0.149 mm), meso (0.149–0.074 mm) and microaggregates (<0.074 mm) were selected for incubation in a dynamic closed system for 30 days under two moisture contents (15 and 30 %, dry weight basis). The CO₂ emissions were quantified using a non-dispersive infrared gas analyzer (IRGA). From total carbon measured, 97 % were found to be SIC. Soil texture is a sandy clay loam with a field capacity and a permanent wilting point of 27 and 17 %, respectively. From whole soil aggregates, 60 % were distributed in fractions lower than 0.25 mm diameter, which are highly erodible by the wind. Soil moisture content had a significant effect on the emission of CO₂. The highest accumulated CO₂ emission was registered in the superficial layer (0.00-0.15 m) within 0.25 mm aggregates (29.4 g m^-2 h^-1), which turned out higher than reported for similar areas. The CO₂ emissions were attributed to the dissolution - reprecipitation process of high concentrations of SIC present in soil, involving a considerable contribution of CO₂ to the atmosphere.

soil respiration; soil incubation; soil carbonates; soil moisture