Soil physical quality varies among contrasting land uses in Northern Prairie regions

Conversion of native grassland to other agricultural land uses can alter soil properties such as organic matter, but little is known about how this impacts soil physical quality indicators in the mixedgrass and aspen parkland natural subregions of the Canadian prairies. This study evaluated soil physical properties in three land use systems (native grasslands, introduced pastures and annual croplands) at seven sites across south-central Alberta, Canada. Hydraulic conductivity (K), pore size fractions and S-index were derived from moisture retention curves measured using a HYPROP system. Fractal aggregation was determined from the mass-diameter relationship of soil aggregates (0.25-8 cm diameter) using 3D laser scanning. All our results, except for K, showed a consistent trend of soil quality differences in the following ranking: native grassland > introduced pasture > annual cropland. Relative to croplands, introduced pastures led to an increase from 9 to 12% in medium-size pores (as median volume fraction of 9-50 μm diameter), whereas this pore fraction in native grassland was 19% (Ps < 0.001). The S-index also detected clear differences in soil quality among land uses, ranging from very low values in annual cropland (0.020), to intermediate in introduced pasture (0.033), and the greatest in native grassland (0.048). Similarly, native grassland had the most frequent and significant fractal aggregation results, indicating a well-developed hierarchical soil structure under native grassland. Certain dynamic soil properties were associated with inherent soil properties; for example, water content at saturation and K were both correlated with clay content (correlation coefficients ≥ 0.89*). Our results suggest that S-index, fractal aggregation and medium-size pore abundance are robust soil physical quality indicators sensitive to contrasting agricultural land uses in northern temperate prairies.