Aggregate Stability of Soils in Central Spain and the Role of Land Management

Abstract

The paper examines the relationships between soil aggregate stability, selected soil properties and land use in central Spain.Aggregate stability indices derived from three procedures were found to be significantly (p > 0.01) correlated with each other as well as with clay content, organic carbon and a range of water-soluble salts. Soils with a higher clay content have a lower aggregate stability. It appears that the presence of expandable clays has a major negative influence, although this impact is strongly modified by recent land-use history and contemporary land-management practices. Agricultural land, abandoned in the 1940s, was subsequently invaded by Cistus matorral or planted with Pinus. The most stable aggregates occur under matorral and may represent a lag of more resistant aggregates surviving past land-use-related erosional processes. Comparisons with aggregates under Pinus however suggest that hydrophobic substances from the Cistus may have increased aggregate stability. Aggregates from areas remaining in cultivation are the least resistant although the stability envelope overlaps with areas under Pinus. These differences may be related to cultivation practices whereby clay-rich subsurface horizons characterized by higher proportions of expandable clays are drawn to the surface, and to enhancement of aggregate stability under forest by fungal hyphae.

Soil structure and management: a review

“…Hydrophobic molecules cause water repellency in soil aggregates and decrease wettability, which may result in increased cohesiveness, decreased dispersivity and reduced SOC decomposition rates. Long-term aggregate stability can be enhanced by the addition of hydrophobic organic materials such as organic wastes containing hydrophobic materials and SOC from plant types such as Cistus rather than Pinus (Ternan et al, 1996). No-till (Hallett et al, 2001) and burning (Poulenard et al, 2001) affect soil hydrophobicity.…”

“…Fungi, arbuscular mycorrhizal fungi (AMF) and glomalin. Fungal hyphae improve aggregate stability (Ternan et al, 1996) by reorientation of clay particles, binding particles with extracellular polysaccharides, and enmeshing particles. Hyphae also enmesh microaggregates to form macroaggregates, suggesting that aggregation increases with hyphal density (Haynes and Beare, 1997).…”

Wildfire impacts on hillslope sediment and phosphorus yields

“…Twenty-five air-dried aggregates of 4.0-5.6 mm diameter were selected from pooled samples from each site burn severity and placed on a 2.8-mm sieve and equilibrated for 24 h at 50% relative humidity. Aggregate stability was assessed using a laboratory-based spray-type rainfall simulator following the standardized techniques described by Ternan et al (1996). Rainfall was simulated at approximately 45 mm h -1 with a mean drop size of 580 μm.…”

Soil aggregate stability under different landscapes and vegetation types in a semiarid area in northeastern Syria

“…It was suggested that wetting by rapid immersion for the measurement of DAS had led to aggregate breakdown by slaking, while the slaking process may not occur in the measurement of WAS. As Ternan et al (1996) and Unger (1997) suggested, the slaking process played a major role in the breakdown of surface soil aggregates in a semiarid area including the study area where intermittent rainfall causes rapid wetting of the relatively dry soil surface (Shinjo et al 2000). Thus, the determination ofDAS was considered to be more suitable than that of WAS for the analysis of soil erodibility.…”