Wet Aggregate Stability of Some Botswana Soil Profiles

Abstract

During intense and short rainfall events, important losses of fertility are expected as a result of erosion in drylands because the nutrient pools are concentrated in the topsoil. Therefore, we evaluated the kinetics of aggregate stability in some Haplargids and Torripsamments in Botswana as it represents a resistance factor against losses of materials, measuring also the release of organic matter and phosphorus during wet sieving. We found very low contents of 1-2 mm aggregates in both soil typesalthough the Haplargids had higher levels of this size aggregate (19%) compared with the Torripsamments (10%)-and no differences between the topsoil and the deeper horizons. The total losses of aggregates were similar in topsoils and deep soil horizons and independent from soil order, but the Entisols had a greater proportion of aggregate breakdown, 38% on the average, when the sample was water-saturated. Only clay and silt content, and cation exchange capacity showed good correlations with aggregate stability. Organic matter or iron oxides had no effect, suggesting that aggregation is the result of cation bridging between mineral particles. Up to 97% of the organic matter released into water was lost at the beginning of the wet sieving, but the amounts were not related to aggregate breakdown, indicating that organic matter, besides not influencing the stability of macroaggregates, had little effect on the stabilization of microaggregates. Phosphorus was also released during the wet sieving, and was related to soil available P (r ¼ 0.713 after 5 min). With no effect of organic matter on aggregate stability, and nutrients concentrated in the topsoil, the vulnerability of these soils to fertility losses is therefore extremely high.

Variation of Soil Physical Properties and Moisture Content Along Toposequences in the Arid to Semiarid Area

“…The increase in clay content increases the stability of soil aggregates and hence decreases its erodibility. Bonifacio et al (2006) reported that clay and silt content showed good correlations with aggregate stability. The analyses indicated a consistent relationship between clay and silt content and land position, slope, and curvature.…”

Effects of freeze–thaw on aggregate stability and the organic carbon and nitrogen enrichment ratios in aggregate fractions

“…The > 0.25 mm water stable aggregate (WSA) fraction, obtained by fractionating the soil into aggregate classes by wet sieving, is considered to be an important index of aggregate stability (Yoder, 1936;An et al, 2009). Therefore, the percentages of macroaggregates (>0.25 mm WSA fraction) can reflect the ability of a soil to resist erosion (Bonifacio et al, 2006;Huang et al, 2010). Some climatic conditions, such as erosive rains and freezethaw, cause the breakdown of macroaggregates, leading to increasing percentages of microaggregates (Barthes & Roose, 2002;Oztas & Fayetorbay, 2003) and a greater tendency for erosion after macroaggregates are disrupted (De Gryze et al, 2007).…”

Contents of soil organic carbon and nitrogen in water-stable aggregates in abandoned agricultural lands in an arid ecosystem of Northwest China

“…Soil aggregate stability is influenced by land use change (e.g. agricultural abandonment) in the way that changes the proportion of WSA sizes (John et al, 2005;Ashagrie et al, 2007) and mean weight diameter (MWD) (Bonifacio et al, 2006). Microaggregates, however, seem to be less influenced by land use change (Puget et al, 2000).…”