## 3 Results
### Variations in Soil Variables after Biochar Application  
Figure 4a shows the map of soil moisture content in the three groups BC1, BC2, and C. The UAV-derived average soil moisture content was significantly higher in biochar amended soils BC1 by 17.7 \(\pm\) 0.1% and BC2 by 10.8 \(\pm\) 0.1% compared with the control (Table 1). The soil moisture content measured by in-situ sensors also showed overall higher values in biochar groups than in the control, but the spatial variations within the group were large (Figure 4b,c, Supplementary Figure S3) and those changes were not statistically significant (Supplementary Table S1). UAV-derived soil matric potential was significantly higher in BC1 biochar by 44.8 \(\pm\) 0.7% and lower in BC2 biochar by \(-\)66.9 \(\pm\) 0.7% than the control (Table 1, Figure 5, Supplementary Figure S4). The soil matric potential measured by in-situ sensors did not vary across treatments (Supplementary Table S1) and the range of spatial variation was also large, from \(-\)1.4 to \(-\)0.2 MPa (Supplementary Figure S4), contrasting to the UAV-derived soil matric potential of about \(-\)0.45 to \(-\)0.06 MPa. The fitted soil water retention curves of biochar groups shifted towards higher soil water content at a given water potential compared to the control (Supplementary Figure S5). \begin{table}
\begin{tabular}{c c c c} \hline \multicolumn{1}{c}{**Variables**} & \multicolumn{1}{c}{\
\begin{tabular}{c} **Bamboo Biochar** \\ **BC1 (\%)** \\ \end{tabular} } &
\begin{tabular}{c} **Sugarcane Biochar** \\ **BC2 (\%)** \\ \end{tabular} \\ \hline \multirow{4}{*}{Soil variables} & Soil moisture content from UAV & 17.7 \(\pm\) 0.1 & 10.8 \(\pm\) 0.1 \\ \cline{2-4}  & Soil matric potential from UAV 1  & 44.8 \(\pm\) 0.7 & \(-\)66.9 \(\pm\) 0.7 \\ \cline{2-4}  & Soil albedo & 0.5 \(\pm\) 0.1 & 1.4 \(\pm\) 0.1 \\ \cline{2-4}  & Soil surface temperature & \(-\)0.7 \(\pm\) 0.2 & \(-\)1.4 \(\pm\) 0.2 \\ \hline \multirow{4}{*}{Leaf and canopy variables} & Gross primary productivity & 41.9 \(\pm\) 3.4 & 17.5 \(\pm\) 3.4 \\ \cline{2-4}  & Normalized difference vegetation index & 10.0 \(\pm\) 1.4 & 7.4 \(\pm\) 1.4 \\ \cline{2-4}  & Canopy chlorophyll content & 32.0 \(\pm\) 3.0 & 10.1 \(\pm\) 3.0 \\ \cline{2-4}  & Water use efficiency & 40.8 \(\pm\) 3.5 & 13.4 \(\pm\) 3.5 \\ \cline{2-4}  & Leaf area index & 6.0 \(\pm\) 1.3 & \(-\)4.9 \(\pm\) 1.3 \\ \hline \multirow{4}{*}{Land surface energy components} & Net radiation & \(-\)0.2 \(\pm\) 0.3 & 2.3 \(\pm\) 0.3 \\ \cline{2-4}  & Latent heat flux (evapotranspiration) & 1.1 \(\pm\) 1.0 & 4.0 \(\pm\) 1.0 \\ \cline{2-4}  & Evaporative fraction & 3.7 \(\pm\) 1.0 & \(-\) 0.2 \(\pm\) 1.0 \\ \cline{2-4}  & Ground heat flux & \(-\)1.8 \(\pm\) 0.6 & 3.5 \(\pm\) 0.6 \\ \cline{2-4}  & Sensible heat flux & \(-\)0.4 \(\pm\) 0.7 & \(-\)0.4 \(\pm\) 0.7 \\ \hline \end{tabular}
\end{table} 
Table 1: Average changes (%) in key variables of biochar groups compared with the control (marginal mean \(\pm\) SE) derived from UAV-derived data. Bold fonts indicate the variations significant at \(p\) < 0.05. The average soil surface albedo values were significantly higher in the two biochar groups, and the soil surface temperature decreased by \(-0.7\)\(\pm\) 0.2% in BC1 and \(-1.4\)\(\pm\) 0.2% in BC2. Measurements of soil samples revealed non-significant changes in soil total nitrogen concentration (Supplementary Table S1). Figure 4: (**a**) Map of volumetric soil water content (\(\theta\)) of three experimental groups from UAV on 14 November 2018. The circle (\(\Circle\)) denote sensor locations. (**b**) Violin plots of the \(\theta\) from UAV in each plot and each treatment. The shaded areas of the violin plot denote the distribution of the day’s measurement, the white dots denote the median values, and the bottom and top edges of the black bars denote the 25 th and 75 th percentiles respectively. The circles (\(\Circle\)) denote sensor measurements during flight.