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Straw management effects on CO2 efflux and C storage in different Mediterranean agricultural soils

Badía, David, Martí, Clara, Aguirre, Angel J.
The Science of the total environment 2013 v.465 pp. 233-239
agricultural soils, barley straw, calcareous soils, carbon, carbon dioxide, carbon sequestration, carbon sinks, correlation, emissions, gypsum, humus, microbial activity, organic matter, saline soils, salts, seasonal variation, semiarid soils, soil organic carbon, soil water, spring, summer
The crop residues buried in semiarid soils as a carbon sink are evaluated. Both C–CO2 evolved and C sequestered from agricultural soils amended with barley straw were measured seasonally over 2 farming seasons in a semiarid environment (NE Spain). Six experimental soils with low organic matter content and contrasted properties were selected.The CO2 efflux, as a result of soil microbial activity, showed a significant seasonal variation according to changes in both soil moisture and temperature being the spring and early summer when respiration rates get higher. On annual average, more organic, calcareous soils, evolved higher carbon dioxide efflux (up to 53mg CO2/kg and day) than soils with high levels of gypsum or more soluble salts (up to 25mg CO2/kg and day), which have a lower percentage of organic carbon. Straw residue incorporation increases these CO2 emissions significantly for each soil type. Although CO2 emissions are significantly and negatively correlated with the C storage, straw addition increases soil organic C content, at the end of the period of study. In calcareous soils were stored up to 550kgC/ha and year, gypseous soils up to 1135kgC/ha and year and saline soils up to 1450kgC/ha and year. According to the amount of stored C in the different soil types, the isohumic coefficient of barley straw ranges from 0.087 to 0.259 (kg of humus formed from 1kg of dry straw).