Myths of slash and burn on physical degradation of savannah soils: impacts on Vertisols in north Cameroon

A study was conducted to assess the impact of agricultural land use history on macro‐aggregate (4.0–4.8 mm) stability in the 0–5 cm layers of Chromic and ‘Hydromorphic’ Vertisols in north Cameroon. Macroaggregate stability to water drop impact was determined and the ASI 50 index calculated. Macroaggregates from fallow and zero‐tilled cropped soils disaggregated in a stepwise manner. Macroaggregates from ploughed cropped soils collapsed in one step into semi‐liquefied microaggregates and primary particles. On both soil types, the ASI 50 index of samples from ploughed land was 10.0 mJ, compared to 16.4– 21.9 mJ from zero‐tilled slash and burn land use. The stepwise disintegration of macroaggregates indicated the existence of a hierarchy of aggregation within the size range 2–5 mm. Slash and burn land use on zero‐tilled Vertisols significantly increased sand‐sized organic carbon content and the stability of macroaggregates to water impact.