Regional Study of No‐Till Impacts on Near‐Surface Aggregate Properties that Influence Soil Erodibility

Abstract

The extent to which tillage systems modify the near‐surface soil aggregate properties affecting soil's susceptibility to erosion by water and wind is not well understood. We hypothesized that an increase in soil organic carbon (SOC) content with conservation tillage systems, particularly no‐till (NT), may improve near‐surface soil aggregate properties that influence soil erodibility. This regional study assessed changes in aggregate resistance to raindrops, dry aggregate wettability, and dry aggregate stability as well as their relationships with changes in SOC content. Four long‐term (>19 yr) tillage systems including moldboard plow (MP), conventional till (CT), reduced till (RT), and NT were chosen across the central Great Plains at Hays and Tribune, KS, Akron, CO, and Sidney, NE. The kinetic energy (KE) of raindrops required to disintegrate 4.75‐ to 8‐mm aggregates from NT soils equilibrated at −0.03 and −155 MPa matric potential was between two and seven times greater than that required for MP and CT soils in the 0‐ to 2‐cm depth in all soils. At the same depth, the water drop penetration time (WDPT) in aggregates from NT soils was four times greater at Akron and Hays and seven times greater at Sidney and Tribune compared with that in plowed soils. Aggregates from NT soils were more stable under rain and less wettable than those from plowed soils particularly in the surface 0 to 5 cm, but RT had lesser beneficial effects than NT management. The SOC content increased with NT over MP and CT and explained 35% of the variability across soils in aggregate wettability and 28% of the variability in resistance to raindrops in the 0‐ to 2‐cm depth. Aggregate wettability explained 47% of the variability across soils in KE of raindrops required for the disintegration of aggregates. No‐till management did not affect dry aggregate‐size distribution and stability except at Akron where mean weight diameter (MWD) in RT and NT was 50% lower than in MP management in the 0‐ to 2‐cm depth. Aggregates in MP and CT soils were either stronger or equally strong when dry but less stable when wet than in NT soils. Overall, NT farming enhanced near‐surface aggregate properties affecting erosion by water but had small or no effects on dry aggregate stability.