Land‐use effects on soil moisture profile dynamics in a restrictive claypan soil

Abstract

Claypan soils of the Central United States are characterized by restricted drainage and a sharp increase in clay content with depth. This results in soil moisture profiles that vary in total water content and in how moisture is distributed across depths. Because the depth of the restrictive clay layer varies across the landscape, comparing moisture at a single fixed depth can misrepresent these profiles. Each profile was therefore characterized as a whole using two metrics. These were moisture level (overall profile wetness) and moisture stratification (the relative distribution of water between shallow and deeper soil layers). Differences in moisture level and moisture stratification, together accounting for 89.3% of the total variance, were evaluated among four land‐use systems at the Ross Jones Research Farm in northeast Missouri. Volumetric water content was measured daily at 10, 20, 30, and 60 cm under corn ( Zea mays L.)–soybean ( Glycine max (L.) Merr.) rotation, Kernza ( Thinopyrum intermedium (Host) Barkworth & D.R. Dewey), alfalfa ( Medicago sativa L.), and pin oak ( Quercus palustris Muenchh.) during 2023 and 2024. Both dimensions varied among land‐use systems and interacted with year ( p  < 0.05). During the drier year (2023, soybean phase), corn–soybean rotation exhibited higher moisture levels than alfalfa, while Kernza and pin oak did not differ significantly from either system. Differences diminished under wetter conditions in 2024 (corn phase). Differences in moisture stratification were most evident under moisture‐limited conditions. Corn–soybean profiles were characterized by greater shallow moisture dominance, whereas pin oak maintained relatively greater moisture at depth. Kernza and alfalfa showed intermediate patterns. Mean shallow–deeper coordination did not differ among systems. Following rainfall events, systems diverged in their reorganization dynamics. Corn–soybean rotation showed a significant negative shift in moisture stratification ( p  < 0.05), indicating progressive separation between shallow and deeper soil moisture during drying. In contrast, Kernza and pin oak maintained stable or positive reorganization patterns. Alfalfa exhibited a weaker, nonsignificant negative response. These findings indicate that land‐use effects in restrictive claypan soils are expressed more strongly through differences in moisture stratification and post‐rainfall redistribution dynamics than through persistent changes in overall moisture level.