Long-term impacts of topsoil depth and amendments on soil physical and hydrological properties of an Alfisol in central Ohio, USA

Soil hydrological properties and aggregate stability are strongly impacted by erosion and management practices. However, magnitudes of the erosion-induced changes in topsoil depth and the attendant alterations in soil properties are not well understood. Therefore, the present study was conducted on a long term (20 years) simulated study of topsoil depth and use of soil amendments to monitor changes in soil hydrological properties, and aggregate stability of an Alfisol at the Waterman Farm of The Ohio State University, Columbus, Ohio. The aim of the study was to compare long-term effects of soil amendments (synthetic fertilizer and organic compost) on soil physical and hydrological properties at varying soil depth. The experimental plots, comprising of five treatments, were laid out in Randomized Block Design and replicated thrice. Treatments were: (1) topsoil removed (20 cm deep), (2) undisturbed topsoil (intact topsoil); with two soil amendments: (a) synthetic fertilizer 150 kg nitrogen (N) ha⁻¹ yr⁻¹, (b) organic compost at 20 Mg ha⁻¹ yr⁻¹, and (3) a permanent grass field (as a benchmark plot). Soil properties, measured for 0–10 cm and 10–20 cm depth, were: texture, aggregate stability, geometric mean diameter (GMD) of aggregates, water retention properties, hydraulic conductivity (Ks), pore size distribution, and plant available water capacity (PAWC). Aggregate stability was the highest (87.9 and 84.7%) in the permanent grass at 0–10 cm and 10–20 cm depths, respectively. Among the cultivated treatments, compost- amended undisturbed plots (87.6 and86.9%) had the highest proportion of water stable aggregates (WSA) at 0–10 cm and 10–20 cm depths, respectively. However, the GMD of aggregates was the highest 4.1 mm (0–10 cm) and 3.5 mm (10–20 cm) for the topsoil removed and compost-amended treatment. Soil texture was silty clay loam in topsoil removed treatments, clay loam in the undisturbed treatment, and loam in permanent grass treatment, probably due to artificial removal of topsoil. Plant available water content was more in the disturbed and undisturbed compost-amended plots for both the 0–10 and 10–20 cm depths, respectively. The highest soil water volumetric content ranged from 0.37 to 0.25 m³ m⁻³ in the topsoil removed fertilizer added compared with 0.34 to 0.24 m³ m⁻³ in undisturbed compost added plots, respectively. However, the pore size distribution was not affected by treatments at the 0–10 cm depth. For the10-20 cm depth, an overall greater pore size distribution range of 0.04 to 0.33 m³ m⁻³ was observed in the permanent grass, and undisturbed compost amended treatments. Soil Ks (cm day⁻¹) for 0–10 cm depth did not differ significantly across treatments. The data obtained enhances the understanding of the impacts of long-term use of amendments on soil water retention and aggregate stability of simulated topsoil removed and undisturbed field under no-till (NT) in corn (Zea mays)–soybean (Glycine max L. Merr.) rotation in the Eastern Corn Belt of the U.S.