## 3 Results  
### Physicochemical Characteristics of Soil and Organic Amendments  
The gob spoil soil was near-neutral with a measured pH of 7.36 \(\pm\) 0.07. While the pH of the compost was 7.81 \(\pm\) 0.02, the pH of the biochar was basic at a pH of 9.70 \(\pm\) 0.01 (Table 1). The OM content of the soil was \(\sim\)28%. Both the organic amendments had higher organic contents, \(\sim\)86% and \(\sim\)49% for the biochar and the compost, respectively. Gob spoil soil was loamy sand in texture with 72% sand, 25.5% silt, and 2% clay (Table 1) with only \(\sim\)40% water-holding capacity. The total P content of the soil was 131.78 mg/kg, but the plant-available P content of the soil was low, at 37.34 mg/kg. On the other hand, the total and plant-available P content of the biochar and the compost were comparatively much higher. For biochar, the total and plant-available P contents were 528.22 mg/kg and 251.79 mg/kg, respectively. For compost, the total and plant-available P were 3167.78 and 1770.80 (mg/kg soil), respectively (Table 1). The total carbon content of the soil was 14.5%, whereas for biochar and compost, the total carbon contents were 50.7% and 25%, respectively (Table 1). The RCRA 8 metal contents in the soil were low. Both the organic amendments showed comparatively low levels of RCRA 8 metal content and hence were considered suitable for use as amendments for the gob spoil soil.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Properties** & **Gob Spoil Soil** & **Biochar** & **Compost** \\ \hline pH & 7.36 \(\pm\) 0.07 & 9.70 \(\pm\) 0.01 & 7.81 \(\pm\) 0.02 \\ \hline EC (dS/m) & 3.78 \(\pm\) 0.01 & 3.29 \(\pm\) 0.09 & 10.05 \(\pm\) 0.34 \\ \hline Organic Matter Content (\%) & 27.75 \(\pm\) 0.83 & 86.43 \(\pm\) 0.58 & 49.31 \(\pm\) 2.11 \\ \hline Moisture Content (\%) & 3.79 \(\pm\) 0.09 & 9.37 \(\pm\) 0.27 & 39.27 \(\pm\) 0.80 \\ \hline Clay (\%) & 2.11 \(\pm\) 0.24 & - & - \\ \hline Slit (\%) & 25.51 \(\pm\) 1.03 & - & - \\ \hline Sand (\%) & 72.38 \(\pm\) 0.80 & - & - \\ \hline Water-Holding Capacity (\%) & 40.00 \(\pm\) 4.00 & - & - \\ \hline Total C (\%) & 14.50 \(\pm\) 1.80 & 50.70 \(\pm\) 7.90 & 25.00 \(\pm\) 4.20 \\ \hline Total N (\%) & 0.30 \(\pm\) 0.03 & 0.20 \(\pm\) 0.02 & 1.80 \(\pm\) 0.22 \\ \hline Total P (mg/kg) & 131.78 \(\pm\) 33.29 & 528.22 \(\pm\) 72.28 & 3167.78 \(\pm\) 227.94 \\ \hline Plant-Available P (mg/kg) & 37.34 \(\pm\) 6.20 & 251.79 \(\pm\) 21.59 & 1770.80 \(\pm\) 21.31 \\ \hline As & 2.43 \(\pm\) 0.29 & 0.64 \(\pm\) 0.14 & 1.22 \(\pm\) 0.08 \\ \hline Ba & 192.35 \(\pm\) 22.50 & 15.35 \(\pm\) 2.61 & 49.76 \(\pm\) 0.68 \\ \hline Cd & 0.65 \(\pm\) 0.09 & BDL 2 & 0.19 \(\pm\) 0.01 \\ \hline RCRA 8 metals (mg/kg, total) 1 & Cr & 4.83 \(\pm\) 1.08 & 0.51 \(\pm\) 0.08 & 2.63 \(\pm\) 0.08 \\ \hline Pb & 7.76 \(\pm\) 2.08 & 0.39 \(\pm\) 0.12 & 0.59 \(\pm\) 0.18 \\ \hline Hg & 0.28 \(\pm\) 0.09 & 3.97 \(\pm\) 0.38 & 3.89 \(\pm\) 0.46 \\ \hline Se & BDL & BDL & 0.38 \(\pm\) 0.26 \\ \hline Ag & 0.17 \(\pm\) 0.11 & BDL & BDL \\ \hline Cu (mg/kg, total) & 14.09 \(\pm\) 2.78 & 4.99 \(\pm\) 0.36 & 12.85 \(\pm\) 1.04 \\ \hline Fe (mg/kg, total) & 7467 \(\pm\) 1217 & 546 \(\pm\) 105 & 2202 \(\pm\) 122 \\ \hline Al (mg/kg, total) & 5414 \(\pm\) 1411 & 745 \(\pm\) 154 & 1803 \(\pm\) 71 \\ \hline Mn (mg/kg, total) & 111 \(\pm\) 21 & 17 \(\pm\) 3 & 130 \(\pm\) 2 \\ \hline \end{tabular} \({}^{\dagger}\) RCRA 8 metals are a group of eight heavy metals that are monitored and regulated by the U.S. Environmental Protection Agency (EPA) as hazardous waste under the Resource Conservation and Recovery Act (RCRA). \({}^{2}\) BDL = Below Detection Limit.  
\end{table}
Table 1: Properties of the gob spoil soil, biochar, and compost samples used in this study.