## 5 Conclusions  
This study demonstrated that the joint use of hyperspectral and thermal imagery from a UAV is promising to provide a wide range of indicators for quantifying upland rice productivity and water usage after biochar application. We showed that the indicators derived from the imagery using physical models were useful in exploring biophysical information behind indirect measurements, and in explaining the mechanisms from the observed changes after biochar application. The integration of direct and indirect measurements allows for the identification of relative changes in plant biophysical variables, soil water availability, and surface energy fluxes. Drone-based remote sensing provided spatially explicit information without disturbing the measurement target, densifying ground point measurements from sensors or laboratory samples, enabling a wide range of applications that can benefit precision agriculture and crop management in general. The results show relatively large increases in GPP, chlorophyll content, and soil moisture content after the biochar amendments. In addition, non-significant or significant but small changes in energy fluxes and evapotranspiration were revealed, suggesting increases in WUE after biochar application. However, the biochar feedstock and application management might have influenced the outcomes as in our case the increment in bamboo biochar amended soil was larger than in sugarcane biochar amended soil. This study motivates a larger scale experiment so that other aspects related to the impact of the amendment for WUE, GPP, and soil fertility can be tested at a full crop scale. The results demonstrate the potential of biochar for agricultural water management to withstand dry spells by allowing rice plants to efficiently use water and nutrients use. A noteworthy result is that potential climate feedbacks derived from high temperatures and dark soils might not be as significant as previously thought, based on the detected changes in the surface energy balance components affecting radiative forcing such as the land surface temperature, albedos, or sensible heat fluxes after limited biochar application in our experiment. Biochar amendment is therefore promising as part of the strategies to improve the resilience of crops under rainfall reduction scenarios associated with the impacts of climate variability and change. The implementation of biochar to improve WUE, soil quality, and likely carbon uptake can also represent an innovative solution to the treatment of agricultural residues and foster good agricultural practices. The following are available online at [[https://www.mdpi.com/article/10.3390/rs13101866/s1](https://www.mdpi.com/article/10.3390/rs13101866/s1)]([https://www.mdpi.com/article/10.3390/rs13101866/s1](https://www.mdpi.com/article/10.3390/rs13101866/s1)), Figure S1. Unsupervised classification using k-means clustering method. Sunlit soil pixels are separated from others for albedo analysis. Figure S2. (a) R\({}^{2}\) and (b) root mean squared difference (RMSD) between the UAV-measured and the Pro4 SAIL-modeled hyperspectral reflectance using the parameters from the model inversion outputs. Histograms show the frequencies of these values over three groups of rice canopy. Figure S3. (a) The comparison of plot-averaged soil moisture content (\(\emptyset\)) in three groups BC1, BC2, and C from UAV over the period Nov 14 to 21, 2018 and during the four UAV campaigns. Whiskers denote the 95% confidence interval of each group on each day. Violin plots of \(\theta\) from UAV in each plot and each treatment on (b) Nov16, (c) Nov 19, and (d) Nov-21. The shaded areas of the violin plot denote 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 red circle '\(\bigcirc\)' denotes sensor measurements during flight. Figure S4.