# Soil health alterations via compost additions to natural and remediated heavy metal-contaminated mineland soils

## TL;DR

Adding compost to metal-contaminated soils improves soil health, but higher compost rates can cause excess phosphorus.

## Contribution

This study identifies optimal compost application rates to improve soil health while managing metal contamination.

## Key findings

- Compost-treated soils showed soil health comparable to native prairie soils.
- Higher compost rates caused excessive extractable phosphorus.
- Plant metal concentrations remained within safe limits for livestock.

## Abstract

The Oronogo-Duenweg mining belt in southwest Missouri is a United States Environmental Protection Agency (EPA) Superfund site due to Pb-contaminated soil and groundwater from historic mining and smelting. Remediation has removed Pb-contaminated overburden, uncovering nutrient-deficient C horizons containing elevated Cd and Zn concentrations, which impede natural revegetation. This study evaluated compost at rates of 180 and 360 Mg ha−1, monitoring changes in soil properties observed at naturally revegetated sites, native prairie locations (i.e., the soil health benchmark), and areas receiving compost treatments. The Soil Management Assessment Framework (SMAF) was employed to assess physical (bulk density (Bd)), water-stable aggregates (WSA)), chemical (pH, electrical conductivity (EC)), nutrient (plant-available P and K), and biological (soil organic C (SOC)), microbial biomass C (MBC), potentially mineralizable N (PMN), and β-glucosidase activity (BG)) soil health indicators and soil health scores. Soil metal concentrations were analyzed using Mehlich-3 and 0.01 M CaCl₂ extractions, while plant metals were extracted with HNO₃ and H₂O₂. Compost-treated soils exhibited overall soil health comparable to native prairie; both had greater overall soil health than the natural revegetation site. However, 360 Mg ha−1 rate led to excessive Mehlich-3 extractable P compared to 180 Mg ha−1. Mehlich-3 extractions revealed that the compost added Cd and Zn to the system, yet Cd and Zn concentrations from the 0.01 M CaCl2 extraction were negligible in the compost-treated soils. Plant heavy metal concentrations were below tolerable limits for livestock consumption. A target compost application rate of 180 Mg ha−1, or lower is suggested for balancing phosphorus and metal concentrations while improving overall soil health.