Soil structure and aggregate stability are critical soil properties affecting water infiltration, root growth, and resistance to soil and wind erosion. Changes in aggregate stability may be early indicators of soil degradation, pointing to low organic matter content, reduced biological activity or poor nutrient cycling. Hence, efficient and reliable aggregate stability measurement techniques are essential for detection, management, and remediation of degraded soil resources. Here we quantify soil aggregate stability by developing a novel proximal sensing technique based on shortwave infrared (SWIR) reflectance measurements. The novel approach is similar to the well-documented high energy moisture characteristic (HEMC) method, which yields a stability ratio (SR) derived from comparison of hydraulic and structural characteristics of slowly- and rapidly-wetted soil samples near-saturation. We rapidly wetted aggregated soil samples (i.e., high energy input) and hypothesized that an aggregate stability index can be derived from SWIR surface reflectance spectra due to differences in post-wetting surface roughness that is intimately linked to aggregate stability. To test this hypothesis, surface reflectance spectra from a wide range of structured soil textures under both slowly and rapidly-wetted samples, were measured with a SWIR spectroradiometer (350-2500 nm). The ratio between pre- and post-wetting spectra was determined and compared with the HEMC method’s volume of drainable pore ratio (VDPR). We found a strong correlation (R2 = 0.87) between the VDPR and the SWIR-derived reflectance index (RI) and also between the SR (R2 = 0.90) and the RI for all soils. These results point to the feasibility and appeal of quantifying aggregate stability using the newly proposed and more time-efficient proximal sensing method.

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