# 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
**Parameter** & **Loamy Sand** & **Loamy Sand + BC** & **Loam** & **Loam + BC** & **Clay** & **Clay + BC** \\ \hline \(U_{t}\) (g/g) & 0.000 a & 0.031 b & 0.000 a & 0.150 b & 0.000 a & 0.134 b \\ \(U_{s}\) (g/g) & 0.061 a & 0.491 b & 0.204 a & 0.717 b & 0.273 a & 0.347 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 \\ \(m\) & 0.239 & 0.358 & 0.131 & 0.331 & 0.084 & 0.239 \\ \hline \end{tabular}
\end{table} 
Table 3: Parameters of the Mualem-van Genuchten model estimated the three considered soils, with and without biochar (BC). \begin{table}
\begin{tabular}{c c c c c c c} \hline
**1**\#1 (cm)** & **Loamy-Sand** & **Loamy-Sand + BC** & **Loam** & **Loam + BC** & **Clay** & **Clay + BC** \\ \hline \(10.2\) & 0.061 a & 0.463 b & 0.204 a & 0.638 b & 0.272 a & 0.346 b \\ \(102\) & 0.058 a & 0.253 b & 0.202 a & 0.365 b & 0.270 a & 0.334 b \\ \(337\) & 0.051 a & 0.139 b & 0.202 a & 0.271 b & 0.261 a & 0.330 b \\ \(714\) & 0.050 a & 0.139 b & 0.189 a & 0.229 b & 0.254 a & 0.291 b \\ \(1020\) & 0.037 a & 0.074 b & 0.178 a & 0.217 b & 0.251 a & 0.268 a \\ \(3396\) & 0.031 a & 0.062 b & 0.168 a & 0.201 b & 0.243 a & 0.249 a \\ \(15\),296 & 0.018 a & 0.047 b & 0.132 a & 0.162 b & 0.203 a & 0.197 a \\ \hline \end{tabular}
\end{table} 
Table 2: Experimental pairs, pressure head, \(\left\lvert\,h\,\right\rvert\) (cm) and gravimetric water content, \(U\) (g/g), obtained for soils loamy sand, loam and clay with and without biochar, by using the [PERSON] pressure plate apparatus. Values followed by the same letter are not significantly different per a two-tailed \(t\)-test (\(p<0.05\)). Soil water retention curves represented as \(\left\lvert\,\left\lvert\,h\,\right\rvert\,\right\rvert\) vs. \(\theta\) were also represented (Figure 1d-f). Since the measured soil shrinkage was negligible both in the BC amended soils and in the soils without BC, constant \(\rho_{\beta}\) values (Table 4) were used to convert \(U\) into \(\theta\) (Equation (4)). The \(\theta\) values of the loamy sand + BC retention curve were systematically higher than those obtained for the loamy sand, with significant differences in the \(\theta\) values that increased at the lowest \(\left\lvert\,h\,\right\rvert\) and at saturation (Figure 1d). This indicated that BC improved the soil water retention at all the considered \(\left\lvert\,h\,\right\rvert\). Instead, the \(\theta\) values of the loam + BC retention curve (Figure 1e) were lower than those obtained for the loam, except for the \(\theta\) values measured at \(\left\lvert\,h\,\right\rvert>180\) cm as well as for \(\theta_{s}\), (Table 4), indicating an increase in the amount of macropores, and a decrease in the amount of micropores. This result indicated a partial improvement in the retention properties of the loam after BC addition. The \(\theta\) values of the clay + BC (Figure 1f) were significantly lower than those obtained for the clay, indicating a non-positive effect of BC, due to formation of a larger number of aggregates or particles leading to smaller inter-aggregate pores than the original ones.