Aggregate breakdown mechanisms as affected by soil texture and organic matter in soils dominated by primary minerals

Abstract

Soil aggregates breakdown mechanisms depend on soil properties such as texture, clay mineralogy and organic matter content. Little is known about the effect of soil properties on aggregate breakdown mechanisms in South African soils. The objective of this study was to establish the relationship between aggregate breakdown mechanisms and selected soil properties in some South African soils dominated by primary minerals. Soil samples with varying properties were collected from the surface 0–0.2 m from 14 ecotopes in Eastern Cape province. Aggregate stability was determined following the fast wetting (FW), slow wetting (SW) and wet stirring (WSt) methods. Soils with high quartz were the least stable due to its inability to bond with other clay minerals or soil organic matter (SOM). In contrast, soils with high kaolinite were the most stable. Slaking was the dominant aggregate breakdown mechanism in most of the studied soils. Aggregate stability was significantly correlated with particulate organic matter (POM) for FW (r² = 0.74, P < 0.05) and SW (r² = 0.64, P < 0.05). It was concluded that increasing POM content in soils through SOM inputs and farming methods that reduce POM mineralisation can reduce slaking during rapid wetting by raindrops.

Keywords: fast wetting, slow wetting, vulnerability coefficient, wet stirring

South African Journal of Plant and Soil 2014, 31(4): 213–218