Organic matter in bare soils of the mediterranean region with a semiarid climate

Bare soils, with different textures, from different areas of the Spanish Mediterranean area with a semiarid climate were studied. Because of the important role that the organic matter plays in these soils, the different C fractions were determined and the dynamics of mineralization of the organic matter was followed by means of soil respiration experiments. Total organic C (TOC) content of these soils was low, as was the extractable C × 100/TOC ratio. Very high overall mineralization rates were observed in those soils of a loam or sandy loam texture. Bare soils having silty‐clayey loam or clayey loam texture had the lowest rate of extractable C mineralization. The lowest values for basal respiration and k × m (microbiological activity) corresponded to soils with high electrical conductivity or low TOC content. The process of C mineralization in these soils occurred in two stages of differing first‐order kinetics, the sandy loam soils showing the highest values. Values for electrical conductivity in the soils were negatively correlated with k × m and basal respiration, while these last two parameters showed a high positive correlation with the water‐soluble carbohydrate content. This parameter, however, was not correlated with the kinetics of organic matter mineralization, although the overall mineralization rate was so related. The potential fertility of these soils (determined by plant growth experiments) was correlated with their water‐soluble carbohydrate content and their microbiological activity.