Compaction of a sandy loam soil not impacted by long-term biosolids applications

Abstract

Soil compaction and soil organic matter (SOM) are critical factors influencing crop growth and soil health, yet their interaction and impact on plant-available water (PAW) remain underexplored. To address this, we investigated a 26-year field experiment on fine sandy loam soil in Washington State, USA, involving three biosolids application rates (0, 4.7, and 10.0 Mg ha⁻¹) applied every four years in a winter wheat-fallow rotation. Compacted and uncompacted strips were created using field-traffic, with additional intact soil cores from uncompacted strips compacted in the laboratory. Intact cores from uncompacted, field-compacted and lab-compacted treatments were analyzed for saturated hydraulic conductivity (K_sat), soil moisture release curves, and bulk density (ρ_b). The change in ρ_b after compaction (Δρ_b) and rebound (Δε) were assessed for lab-compacted cores. Disturbed soil samples were analyzed for Proctor maximum bulk density (ρ_bmax), critical water content (CWC), and contact angle (α). Biosolids application generally reduced ρ_b and ρ_bmax, increased CWC, volumetric water content at saturation (θ_SAT), K_sat, and α but did not affect volumetric water content at field capacity (θ_FC), permanent wilting point (θ_PWP), or PAW. Compaction reduced θ_SAT and K_sat while increasing ρ_b, θ_FC, θ_PWP, and PAW. While compaction impacted soil physical and hydraulic properties, biosolids had limited effects under the study conditions. Contrary to our expectations, no interaction between biosolids application and compaction treatments was observed. Despite numerous benefits of increased SOM with biosolids application, increased resistance to and recovery from soil compaction does not appear to be one of them in this study.