A practical, reproducible laboratory method for assessing soil aggregate stability

Abstract

Soil aggregate stability is an important soil physical measurement that is closely related to a range of soil health functions. It is defined by its analytical method and often within-method variability and inter-method comparability have not been addressed and quantified. The current Natural Resources Conservation Service Kellogg Soil Survey Laboratory (KSSL) method for analyzing aggregate stability uses non-standardized equipment and hand-sieving techniques and is not easily scalable. The objective of this study was to evaluate and modify an alternative method that uses a single sieve mechanical wet sieving apparatus (MWS method) to produce results comparable to the current KSSL method and evaluate another alternative method that uses multiple sieves in a custom-fabricated Yoder-type apparatus. The two methods were evaluated for efficiency, repeatability, and scalability. The MWS method uses standardized equipment and methods, which should be scalable and reproducible in different laboratories. Sample preparation, pretreatment, and sieving parameters of the MWS method were adjusted to produce analytical results which most closely matched the KSSL method. Repeated analysis of soil sample standards showed that within-method variability of the MWS method was slightly less than in the KSSL method. In a comparison of 90 samples of widely varying properties, Lin's concordance correlation coefficient was 0.927, indicating a moderate strength of agreement between the MWS method and KSSL method. Results from a modified Yoder method were not comparable to the KSSL method, and the greater time requirements, procedural complexity, and large equipment footprint were identified as practical limitations for use in large-scale laboratory applications.