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The effects of fire and the conversion to vineyard on soil organic carbon (SOC), and soil aggregate size distribution and stability were studied in a forest of Iran. For this purpose, topsoil was sampled in an unburned area, a portion of the forest burned three years earlier, and a vineyard, all three contiguous and showing similar topographic features. In the burned forest, soil was sampled in areas undergone high, moderate, or low severity. Air-dried soil samples were sieved to obtain four aggregate size classes, which were subsequently wet sieved. Soil aggregate distribution index, mean weight diameter, geometric mean diameter, and aggregate stability index were determined on both dry and wet specimens. No significant differences in SOC between burned and unburned forest were found, most probably because of the supply of charred biomass to soil, while in the vineyard thirty years of cultivation had removed half of initial SOC. Both severe fire and cultivation had decreased the stability of aggregates and the relative amount of the biggest ones (8 to 2-cm diameter). However, aggregate stability was significantly lower in the vineyard than in the burned forest, which points out to a stronger impact of prolonged cultivation than a single fire, although severe. Cultivation and severe fire had decreased the proportion of C in macroaggregates, to the advantage of meso (1 to 0.25 mm) and micro (<0.25 mm) aggregates. A hierarchical cluster analysis of all investigated properties and indices demonstrated that cultivation and highly severe fire both were causes of soil degradation. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The number of spores of vesicular-arbuscular mycorrhizal (VAM) fungi occurring in the rhizospheric soil of 14 crops was investigated using traditional wet-sieving/decanting methods. The aim of the study was to determine the effect of some agronomy species (Gramineae, Leguminosae, Solanaceae, Labiatae, Cruciferae, Umbellifera, and Alliaceae) on VAM spores numbers in the rhizosphere. The agronomy species were planted under greenhouse conditions in pots containing semiarid soil. The number of spores in the rhizosphere of each species was studied at the middle and end of vegetative plant growth. In the middle of vegetative growth the number of spores increased significantly in the rhizosphere of some species compared to the control (152 spores 10 g-1 dry soil). The number of spores was lower in Raphanus sativa rhizospheric soil (115 spores 10 g-1 dry soil) and higher in Zea mays rhizospheric soil (255 spores 10 g-1 dry soil). At the end of vegetative growth the number of spores increased only in the rhizosphere of Triticum aestium, Zea mays, Trifolium repens, Solanum tuberosum, Satureja hortensis, and Allium cepa, and this increase was significant. In this stage of plant growth the number of spores was lowest in Raphanus sativa rhizospheric soil (126 spores 10 g-1 dry soil) and highest in A. cepa rhizospheric soil (453 spores 10 g-1 dry soil). [ABSTRACT FROM AUTHOR]