Impacts of biosolids application on soil quality under alternate year no-till corn–soybean rotation

Biosolids are a source of recycled organic matter and nutrients. To evaluate the impact of biosolids application (1984–2008) on soil quality, composite soils (Genesee silt loam, fine loamy, mixed, nonacid, and mesic typic udifluvent) were randomly sampled at geo-referenced sites from 0 (control), 2, 5, and 25 years of lime-stabilized anaerobically digested biosolid-applied fields. Results showed that microbial biomass C (Cₘᵢc), N (Nₘᵢc), and P (Pₘᵢc) contents were significantly higher at both depths of the 5 and 25 years of biosolid-applied fields compared to the control. Biosolid application significantly enlarged the biologically labile C (Cₘᵢc over total organic C, Cₘᵢc:Cₒᵣg) and N (Nₘᵢc over total N, Nₘᵢc:TN) pools with an associated decrease in metabolic C loss (20–53 %) by specific maintenance respiration (qCO₂) relative to the control. The Cₒᵣg, active (AC) and soluble C (SC), TN and reactive N (RN), and reactive P (RP) contents were significantly higher in the long-term biosolid-applied fields than in the control. However, there was an indication of leaching of SC, RN, and RP between depths. Years of biosolid application significantly increased soil moisture content (θ ᵥ at −0.03 MPa) by 20–40 %, macroaggregate stability (MaA) by 2–44 %, and mean weight diameter (MWD) of aggregates by 7–51 %, respectively. Consequently, there was a decrease in soil bulk density (ρ b) and microaggregate stability (MiA) at both depths. Results confirmed that biosolids application at rates recommended is a viable management option to improve soil quality for crop production. However, long-term and repeated biosolid applications above the recommended agronomic N and P rates may be responsible for accumulation and consequent leaching and runoff of SC, RN, and RP to cause groundwater and surface water pollution with environmental consequences.