# Biochar Amended Soils and Water Systems: Investigation of Physical and Structural Properties
## 3 Results and Discussion
### Bulk Density, Soil Water Retention and Plant Available Water
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Loamy Sand** & **Loamy Sand + BC** & **Loam** & **Loam + BC** & **Clay** & **Clay + BC** \\ \hline \(\theta_{s}\) (cm cm\({}^{-3}\)) & 0.084 a & 0.407 b & 0.226 a & 0.520 b & 0.329 a & 0.263 b \\ \(\theta_{r}\) (cm cm\({}^{-3}\)) & 0.000 a & 0.026 b & 0.000 a & 0.109 b & 0.000 a & 0.102 b \\ \(\alpha\) (cm\({}^{-1}\)) & 0.003 & 0.034 & 0.001 & 0.067 & 0.001 & 0.003 \\ \(N\) & 1.315 & 1.558 & 1.150 & 1.494 & 1.091 & 1.314 \\ \hline \(\theta_{\mathrm{app}}\) (cm cm\({}^{-3}\)) & 0.025 a & 0.039 b & 0.146 a & 0.117 b & 0.246 a & 0.149 b \\ \(\theta_{fc}\) (cm cm\({}^{-3}\)) & 0.071 a & 0.115 b & 0.224 a & 0.196 b & 0.315 a & 0.250 b \\ \(\rho_{b}\) (g cm\({}^{-3}\)) & 1.381 a & 0.828 b & 1.110 a & 0.726 b & 1.208 a & 0.757 b \\ PAW (cm\({}^{3}\)cm\({}^{-3}\)) & 0.0456 a & 0.0762 b & 0.0782 a & 0.0791 a & 0.0692 a & 0.1045 b \\ PAW\({}_{\mathrm{U}}\) (g g\({}^{-1}\)) & 0.0330 a & 0.0920 b & 0.0705 a & 0.1090 b & 0.0573 a & 0.1330 b \\ \hline \end{tabular}
\end{table} 
Table 4: Measured wilting point, \(\theta_{\mathrm{app}}\), field capacity, \(\theta_{fc}\), and bulk density, \(\rho_{b}\), for the three considered soils amended and not amended with biochar. Within each raw, values followed by the same letter are not significantly different per a two-tailed \(t\)-test (\(p<0.05\)). Figure 1: Experimental pairs (**a–c**) (\(U\), \(\left\lvert\,h\,\right\rvert\)) obtained by using the Richards pressure plate laboratory methods and (**d–f**) the corresponding pairs (\(\theta\), \(\left\lvert\,h\,\right\rvert\)) obtained for loamy sand, loam and clay soils with and without biochar (BC). Black dots refer to not amended soils, whereas white dots refer to BC-amended soils. Lines indicate the VG water retention curves. Also, the saturated water content, \(\theta_{s}\) obtained for the clay + BC was significantly lower than that obtained for the clay, indicating a decrease in the amount of macropores. Comparing the \(\theta\) and the \(U\) values measured at the fixed \(|h|\), (Figure 1) it appears evident that for the clay, the \(U\) values measured after BC addition were higher than those measured before BC addition (Figure 1c), but the opposite was found in terms of \(\theta\) values (Figure 1f). The loam shows the same trend, except for the \(\theta\) values at \(|h|\leq 180\) cm (Figure 1b,e). The loamy sand, instead, the same behaviour can be observed between the \(U(h)\) and the \(\theta(h)\) functions before and after BC addition (Figure 1a,d), with both the pairs (\(U,h\)) and (\(\theta\), \(h\)) increasing after BC addition, mainly near the low matric potentials (\(|h|\)). Reductions in the dry bulk density, \(\rho_{\beta}\), of the soil + BC mixtures, obtained for the loamy sand, for the loam and for the clay, expressed as ratios \(\rho_{b,\text{soil}}/\rho_{b,\text{soil+BC}}\), were equal to 1.67, 1.53 and 1.60, respectively. However, the \(\rho_{b}\) reduction did not determine an increase the \(\theta\) values in the BC-amended loam (except for the \(\theta\) values at \(|h|\leq 180\) cm) and in the BC-amended clay, compared to the increase observed on the \(U\) values, because for these two soils the ratios \(U_{\text{soil+BC}}/U_{\text{soil}}\) (average ratio \(U_{\text{soil+BC}}/U_{\text{soil}}=1.33\) for the loam and 1.11 for the clay) were lower than the ratios \(\rho_{b,\text{soil}}/\rho_{b,\text{soil+BC}}\). (1.53 and 1.60). Instead, for the loamy sand, the ratio \(U_{\text{soil+BC}}/U_{\text{soil}}\) was higher (average ratio = 2.73) than the ratio \(\rho_{b,\text{soil}}/\rho_{b,\text{soil+BC}}\), (1.67), and therefore the \(\theta\) values obtained after BC addition were higher than those measured in the non-amended loamy sand. This explains why BC had the effect of increasing the \(\theta\) values in the loamy sand, whereas \(\theta\) values lower than those obtained before BC addition were obtained for the clay and, partially, for the loam.