Macroaggregate persistence: Definition and applications to describe soil surface dynamics

Abstract

Macroaggregates (diameter > 0.25 mm) help the soil surface to resist erosive forces, but their contribution to soil surface stability changes with time because macroaggregate formation and disintegration is a dynamic process. Surface macroaggregates can be visualized by advanced image analysis, a non-invasive method to track aggregates. The objective of this study was to develop a mathematical method to describe the spatial and temporal dynamics of surface macroaggregates observed in digital images. We define aggregate persistence as the ability of aggregates to remain in a pre-determined spatial unit throughout a given time span. The first index explains how many aggregates with the same size distribution remain on a soil surface area through time, which we call the Grouped Aggregate Persistence Index (GAPI). The proportion of individual aggregates with the same size, shape and location at the beginning and end of a measurement period is the Individual Aggregate Persistence Index (IAPI). We calculate the GAPI and IAPI for macroaggregates on the surface of a clay agricultural soil, as an example. Photographs of the soil surface (55 cm2) are analyzed with a customized MATLAB program that uses the watershed method to calculate the macroaggregate size distribution for the GAPI and identify the size, shape and location of macroaggregates for the IAPI. These persistence indices are a non-destructive way to describe dynamic changes in macroaggregates at the soil surface, which is complementary to other methods that visually evaluate the soil structure.