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.