Land-use and tillage contrasts in soil aggregate stability and near-surface shear resistance in a subtropical headwater catchment

Aggregate stability and near-surface shear resistance represent complementary expressions of soil structural condition, yet it remains unclear whether they respond similarly to land use and tillage or are associated with different soil properties across heterogeneous headwater catchments. We evaluated 69 georeferenced surface-soil locations (0–0.05 m) under natural forest (NF), grassland forage (GF), conventional tillage (CCT), no-tillage (CNT), and minimum tillage (CMT) in southern Brazil. Soil organic carbon in the selected 1–2 mm aggregate fraction (SOC 1–2 ), clay flocculation in the 1–2 mm fraction (FD 1–2 ), aggregate stability (AS), particle-size fractions, gravimetric soil water content (GSWC), and a Torvane index of near-surface field shear resistance were evaluated using a priori contrasts, Spearman correlations, and principal component analysis (PCA). Relative to the mean of permanent-vegetation land uses, cultivated land had 49% lower SOC 1–2 , 27% lower FD 1–2 , 8% lower AS, and 70% lower shear-resistance. SOC 1–2 was strongly associated with AS (Spearman r = 0.73) but was essentially unrelated to the Torvane index (r = 0.04). In contrast, the shear-resistance index was more closely associated with GSWC (r = 0.48) and silt in the 1–2 mm fraction (r = 0.34). Differences among tillage systems within cultivated land were generally small, except for greater AS under CNT than CMT. The first two principal components explained 53.7% of the standardized multivariate variation. Overall, land use was more strongly associated with near-surface soil structural condition than tillage system, while AS and field shear resistance captured complementary, non-interchangeable aspects of soil structural organization. AS was more closely related to SOC 1–2 and FD 1–2 , whereas near-surface shear resistance was more closely associated with contemporaneous GSWC and particle-size and soil-class conditions. These findings show that land use is a stronger determinant of near-surface soil structural condition than tillage system, and that aggregate stability and field shear resistance provide complementary, non-interchangeable information for assessing soil structural organization and supporting land-management decisions in heterogeneous headwater catchments.