## 3 Results and Discussion
### Phase I: Greenhouse Column Study
#### 3.2.4 Mass Balance of Cu in Greenhouse Column Study  
As shown in Table 3, there was no increase in Cu content in pods and seeds of camelina grown with increasing compost rates. However, the total Cu content in camelina plants increased with the increasing compost rate. Stem and leaves showed increasing Cu content with increase in the compost rate (Table 3). In the case of field pennycress, the overall Cu content (\(\mu\)g) in roots, stems, and leaves increased with the increase in compost rate (except a decrease in stem and leaves, at 10% compost rate). In seeds, Cu content increased at 10% and 20% compost rates. In both camelina and field pennycress, leaves had the highest Cu content, followed by stems, roots, pods, and seeds (Table 3). Seeds had the least amount of Cu in both camelina and field pennycress. Total plant Cu content in all treatments combined was 1.30 mg and 1.31 mg, respectively. Cu content (mg) in leachates increased with increasing compost rate in both camelina and field pennycress planted columns (Table 3). However, the total amount of Cu leached was small. The total amount of Cu in leachates in all compost rates combined was 203 mg and 165 mg, respectively. As shown in Table 3, the majority of the Cu remained in the stamp sand, although small amounts of Cu loss occurred in the leachate. Several studies have demonstrated that compost generated from biomass can be successfully used to improve soil nutrient levels and water holding capacity. Composts may bind heavy metals in soil by changing the pH and providing more sorption sites for binding heavy metals [23]. There are also reports of composts mobilizing metals, due to the presence of dissolved OM that can form soluble complexes with metals [24]. Increase in microbial population, due to increased nutrients and carbon, due to compost amendment and plant growth, may result in the degradation of OM, resulting in the mobilization of metals. Previous reports have shown that the amendment of soils with organic compost having high dissolved organic carbon (DOC) resulted in increased metal leaching [25]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Plant Species** & **Roots** & **Stem** & **Leaves** & **Pods** & **Seeds** & **Total Biomass** \\ \hline Camelina & & & & & & \\ Compost–2.5\% & 0.08\({}^{\mathrm{c}}\) & 0.96\({}^{\mathrm{c}}\) & 0.47\({}^{\mathrm{c}}\) & 0.12\({}^{\mathrm{d}}\) & 0.09\({}^{\mathrm{c}}\) & 1.72\({}^{\mathrm{e}}\) \\ Compost–5\% & 0.14\({}^{\mathrm{c}}\) & 0.97\({}^{\mathrm{c}}\) & 0.58\({}^{\mathrm{c}}\) & 0.05\({}^{\mathrm{d}}\) & 0.04\({}^{\mathrm{bc}}\) & 1.78\({}^{\mathrm{e}}\) \\ Compost–10\% & 0.12\({}^{\mathrm{c}}\) & 2.10\({}^{\mathrm{b}}\) & 0.85\({}^{\mathrm{c}}\) & 0.51\({}^{\mathrm{b}}\) & 0.37\({}^{\mathrm{bc}}\) & 3.96\({}^{\mathrm{cd}}\) \\ Compost–20\% & 0.44\({}^{\mathrm{bc}}\) & 3.53\({}^{\mathrm{a}}\) & 2.86\({}^{\mathrm{b}}\) & 0.18\({}^{\mathrm{cd}}\) & 0.19\({}^{\mathrm{bc}}\) & 7.21\({}^{\mathrm{b}}\) \\ Field Pennycress & & & & & & \\ Compost–2.5\% & 0.11\({}^{\mathrm{c}}\) & 0.50\({}^{\mathrm{c}}\) & 0.68\({}^{\mathrm{c}}\) & 0.24\({}^{\mathrm{cd}}\) & 0.21\({}^{\mathrm{bc}}\) & 1.74\({}^{\mathrm{e}}\) \\ Compost–5\% & 0.11\({}^{\mathrm{c}}\) & 0.81\({}^{\mathrm{c}}\) & 1.31\({}^{\mathrm{c}}\) & 0.35\({}^{\mathrm{bc}}\) & 0.30\({}^{\mathrm{bc}}\) & 2.89\({}^{\mathrm{de}}\) \\ Compost–10\% & 0.78\({}^{\mathrm{ab}}\) & 0.81\({}^{\mathrm{c}}\) & 2.76\({}^{\mathrm{b}}\) & 0.53\({}^{\mathrm{b}}\) & 0.65\({}^{\mathrm{b}}\) & 5.53\({}^{\mathrm{c}}\) \\ Compost–20\% & 1.03\({}^{\mathrm{ab}}\) & 2.26\({}^{\mathrm{b}}\) & 8.05\({}^{\mathrm{a}}\) & 1.40\({}^{\mathrm{a}}\) & 1.30\({}^{\mathrm{a}}\) & 14.0\({}^{\mathrm{a}}\) \\ \hline \hline \end{tabular} Data are reported as mean (n = 3). Means are compared by Tukey Kramer-HSD test (\(\alpha\) = 0.05). The treatment levels that are not connected by the same letter are significantly different from each other.  
\end{table} 
Table 2: Plant yield (oven dried; g) of camelina and field pennycress in the column study.