Surface-soil properties and water contents across two watersheds with contrasting tillage histories

Soil properties and water contents (theta) vary spatially, but management effects on spatial patterns are poorly understood. This study's objective was to compare surface-soil properties and theta in two small watersheds (30-43 ha) in Iowa's loess hills. Both watersheds were in continuous corn (Zea mays L.) from 1972 through 1995, one (CW1) under conventional tillage and the other (RW3) under ridge tillage. In 1996, CW1 was converted to no-till. Surface-soil (0-0.2 m) samples were collected along hillslope transects during 2002 and 2003, including four dates with water-content measurements by gravimetry in both watersheds. Soil bulk density (rho(h), organic carbon (OC), and texture were determined, along with terrain attributes (elevation, slope, surface curvature, contributing area, and wetness index). After accounting for landscape-position effects, RW3 had more OC (2.1 versus 1.7%) and smaller rho(b) (1.16 versus 1.25 Mg m(-3)) than CW1 (P < 0.001). Larger theta values occurred in RW3 (P < 0.002) when 0 was > 33%. Landscape position and terrain attributes better explained variation in 0 in RW3 than CW1. Also, OC was correlated with 0 in RW3, but not in CWL Soil textures were similar (within 2%,) but finer in CW1 (P < 0.05). Pedotransfer functions confirmed that differences in soil properties between watersheds resulted in greater theta in RW3 than CW1, particularly at low soil-water potential, and that more distinct patterns of theta should occur in RW3. Results indicate long-term conventional tillage in CW1 affected soil properties and water-holding characteristics in ways that decreased water retention and muted spatial patterns of theta.