## Materials and Methods
### Soil Pre-Incubation  
Collected soil was sieved to <2 mm particle size and thoroughly homogenized by hand. Biochar, air-dried composted manure, and an inorganic fertilizer were applied to the soil as one-time applications at the beginning of a pre-incubation period, resulting in three \"soil + amendment\" treatments (BIOC, COMP, and INF, respectively), plus an unamended control soil (UNAM). Table 2 summarizes the chemical properties of the amendments. The biochar was obtained from High Plains Biochar in Laramie, WY, produced via pyrolysis of urban tree waste, primarily _Populus deltoides_ L. (Plains Cottonwood), at 760-815 \({}^{\circ}\)C for 10-15 min. The biochar was further treated with an EM-10 microbial inoculant produced by Teraganix, along with worm casting tea and humic acid. The compost consisted of cow and horse manure mixed during stockpiling and aged outdoors for at least one year. It was sourced from the Livestock Unit of the University of Wyoming Laramie Research and Education Center. The inorganic fertilizer applied was commercially available water-soluble Miracle-Gro All Purpose Plant Food(tm).  
Biochar and compost were both added at a rate equivalent to 7.5% of the total weight of the soil + amendment mixture (925 g soil: 75 g amendment). The treatments were thoroughly mixed by hand and, together with the unamended control, tap water was added to increase the moisture content to about 23% total moisture by weight, with native soil averaging about 4% moisture (_w/w_) prior to amendment. Inorganic fertilizer was applied at a rate of 0.0075% crystals to soil (_w/w_), or 0.75 g crystals: 10,000 g soil. A level tablespoon of crystals was weighed six times, establishing an average weight of 12.40 g of crystals per tablespoon. The crystals were dissolved in tap water at the manufacturer's recommended rate of one tablespoon per gallon for outdoor plants, or 12.40 g per 3785.41 mL, then incorporated into soil to achieve 23% total moisture by weight.  
The treatments were stored in plastic trays loosely covered with plastic wrap to reduce evaporation and kept in a dark room at 21 \({}^{\circ}\)C for a pre-incubation period of 22 weeks. Soil moisture was monitored twice a week and additional tap water was added as needed to bring the moisture to about 23%. No drainage was allowed in order to avoid leaching of nutrients or metals during pre-incubation.  
\begin{table}
\begin{tabular}{c c} \hline
**Soil Metrics** & **Soil Measurement** \\ \hline Texture & Sandy Clay Loam \\ Moisture (g g g\({}^{-1}\)) & 0.04 (0.01) \\ pH (1:2 soil: water) & 7.4 (0.1) \\ EC (\(\mu\)S cm\({}^{-1}\)) & 553 (3) \\ Total Organic Carbon (TOC) (mg kg\({}^{-1}\)) & 36,793 (1638) \\ Inorganic Carbon (IC) (mg kg\({}^{-1}\)) & 17,573 (248) \\ Total Nitrogen (mg kg\({}^{-1}\)) & 2123 (15) \\ Inorganic Nitrogen (INN) (mg kg\({}^{-1}\)) & 9.90 (0.4) \\ Potentially Mineralizable Nitrogen (PMN) (mg kg\({}^{-1}\)) & 1.53 (0.29) \\ Dissolved Organic Carbon (DOC) (mg kg\({}^{-1}\)) & 282 (12) \\ Dissolved Organic Nitrogen (DON) (mg kg\({}^{-1}\)) & 2.09 (0.55) \\ Available Phosphorus (AP) (mg kg\({}^{-1}\)) & 0.27 (0.01) \\ Total Pb (mg kg\({}^{-1}\)) & 733 (29) \\ Available Pb (mg kg\({}^{-1}\)) & 111 (8) \\ Total Fe (mg kg\({}^{-1}\)) & 20,703 (386) \\ Available Fe (mg kg\({}^{-1}\)) & 8.87 (0.48) \\ \hline \end{tabular}
\end{table}
Table 1: Characteristics of native soil collected at beginning of pre-incubation. Data presented as average values with standard error in parentheses (_u_ = 3).