Pedogenic and climatic controls on tillage-induced hydro-structural dynamics in eurasian mollisols

Abstract Mollisols of the Eurasian steppe belt are highly productive soils whose hydraulic functioning depends on aggregate hierarchy and management-induced structural dynamics. This study compared the hydro-structural properties of two pedogenic endmembers: the Chinese Isohumusol (monsoon-influenced) and the Ukrainian Chernozem (continental-influenced). Field experiments quantified aggregate size distribution, aggregate stability indices (Mean Weight Diameter, MWD; Geometric Mean Diameter, GMD), bulk density, and seasonal infiltration dynamics to evaluate hydro-structural resilience under contrasting tillage. The Isohumusol exhibited a coarse, depth-stratified architecture with a high proportion of very coarse > 10 mm aggregates and high surface stability under No-Till (MWD = 2.84), supporting peak initial infiltration rates (> 700 mm h⁻1). However, this structure was susceptible to seasonal densification with surface bulk density increasing by 16% from spring to summer and significant degradation under conventional tillage. In contrast, the Chernozem displayed a more homogeneous structure dominated by stable 2–10 mm aggregates, maintaining high stability across the profile (MWD up to 3.01). Its matrix-dominated pore system resulted in lower infiltration rates (< 600 mm h⁻1) but greater resistance to structural collapse, as reflected by a stable fractal dimension (D ≈ 2.47). Reduced tillage systems in the Chernozem increased subsoil bulk density (> 1.35 g cm⁻3), signaling compaction risks. These findings demonstrate that infiltration dynamics and structural stability are fundamentally governed by soil-specific pedogenic templates and seasonal abiotic drivers, necessitating regionally tailored conservation tillage strategies.