Exploratory assessment of the SLAKES method to characterize aggregate stability across diverse soil types

Classical soil aggregate stability (AS) methods lack standardized protocols and require long measurement times. However, the fairly new SLAKES method purportedly allows for rapid AS estimation with minimal technical equipment. SLAKES has been tested on fine-textured soils but its suitability for other soil types is unknown. This study investigated SLAKES’ suitability for AS measurements on silty clay, silt loam, and sandy loam soils. For each SLAKES test, three aggregates were immersed in distilled water and imaged for 10 min. SLAKES output includes disaggregation data per aggregate and three coefficients from a Gompertz function that describe slaking dynamics. Four AS descriptors obtained from SLAKES output were investigated: the averaged maximum slaking from a test (a_SK), the maximum slaking for each measurement (aggregate) (a_FT, from fitting a Gompertz function to SLAKES raw data), the averaged a_FT for the measurements in a test (a̅_FT), and the slaking index at 10 min per measurement (SI₆₀₀). The a_SK is a direct descriptor included in the SLAKES output, while a_FT, a̅_FT, and SI₆₀₀ are indirect descriptors. The SI₆₀₀ was the most preferred SLAKES AS descriptor since it is a calculated parameter and due to its sensitivity in detecting AS status among all soil types. The sandy loam soil was the most stable from both the raw SLAKES data and fitting, albeit counterintuitive. SLAKES default measurement time was sufficient for the silty clay and silt loam soils but not for the sandy loam soil. Overall, SLAKES was a useful tool for AS measurements on fine-textured soils but was less suitable for AS measurements on the coarse-textured soil.