# 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  
The \(U\) value measured at the considered \(\mid\!h\!\mid\) values increased when BC was added to the three soils, with the differences being significantly different (\(p<0.05\)), except for the \(U\) values measured for the clay soil at \(\mid\!h\!\mid\geq 1020\) cm. The average gravimetric water contents, \(U\) (g/g), corresponding to the applied pressure head values, \(\mid\!h\!\mid\), for the soils loamy sand, loamy sand + BC, loam, loam + BC, clay and clay + BC has been evaluated (Table 2). For the three soils, BC significantly increased both the water content at saturation (\(U_{s}\)) and the residual water content (\(U_{I}\)), also increasing \(\alpha\) and \(n\). The Mualem-van Genucthen parameters obtained by fitting Equation (6) to the (\(U\), \(\left\lvert\,h\,\right\rvert\)) pairs of the three BC-amended and non-amended soils were considered to explain the BC activities (Table 3). PAW\({}_{\text{U}}\) (g/g) significantly increased from 0.033 to 0.092 for the loamy sand, from 0.0705 to 0.109 for the loam and from 0.0573 to 0.133 for the clay, after BC application (Table 4). Differences (%) between the PAW measured in the BC amended soils and in the original soils were equal to 178%, 54.7% and 131.6% for the loamy sand, loam and clay respectively, showing that the effect of BC was in the order loamy sand \(>\) clay \(>\) loam. The bulk density, \(\rho_{b}\) obtained for the non-amended and for the BC amended soils shows has the values of bulk density is a multivariate parameter affect by the mineral and organic material in which no linear definition is considerable (Table 4). The lower bulk densities in clay + BC originate from mixing the lower density material in the clay soil, is consistent with a no significant changes in aggregate structure. The phenomenon has been previously reported in a field study conducted by [PERSON] et al. (2018) on clay soil also by using forest biomass BC. Therefore, appear more considerable from the reported laboratory experiment result that demonstrate as changes in the soil's physical properties due to BC addition depend on soil type, instead of BC's capacity to store water in its internal structure is immutable parameter. The \(\rho_{b}\) measured for the BC, equal to 0.173 g/cm\({}^{3}\) (Table 1) was considerably lower than that measured in the non-amended soils, equal to 1.38 g/cm\({}^{3}\), 1.11 g/cm\({}^{3}\) and 1.20 g/cm\({}^{3}\) for the loamy sand, for the loam and for the clay, respectively. As a consequence of BC addition, \(\rho_{\beta}\) (g/cm\({}^{3}\)) significantly decreased from 1.38 to 0.828 in the loamy sand + BC, from 1.11 to 0.726 in the loam + BC, and from 1.208 to 0.757 in the clay + BC, with ratios equal to 1.67, 1.53 and 1.60, respectively, between the \(\rho_{\beta}\) of the non-amended soils and the \(\rho_{\beta}\) of the BC-amended soils. The decrease in \(\rho_{\beta}\) due to BC application ([PERSON] et al., 2018) agrees with the results of previous investigations ([PERSON] et al., 2018; [PERSON] et al., 2019; [PERSON] et al., 2020), and it is due to a mixing or dilution effect ([PERSON] et al., 2019) determined by the difference between the \(\rho_{\beta}\) of the non-amended soils and of BC. The soil water retention curves, expressed as \(\left\lvert\,h\,\right\rvert\) vs. the gravimetric water content \(U\) (g/g), evidencing that the considered standard soils were characterized by a very poor water retention before BC application (Figure 1a-c).