## 3 Results
### Remote Sensing Responses  
For illustrative purposes Figure 4 displays spectra from soybean and maize plants, comparing both crops among soil water levels (Figure 4A,B) and days of measurements (DoM) (Figure 4C,D). The seasonal average reflectance of soybean was about 10% higher than maize in near infrared (NIR) bands (760-950 nm), which could indicate higher seasonal LAI for soybean than maize [42]. In the red-edge and NIR regions, reflectance was slightly lower for wet plants (100% WHC) for both crops (Figure 4A). In the VIS, wet maize plants also showed lower NIR reflectance, while soybean plants showed the opposite (Figure 4B). Over time, there was a marked increase in reflectance, especially for maize plants and in NIR wavelengths (Figure 4C,D). Analysis of seasonal responses to soil drought and phenology responses on remote sensing variables is shown in Table 4, Figure 5, and Figure S1. Soybean \(\mathrm{T_{L,Rad}}\) was significantly lower between dry (40% WHC) and wet (100% WHC) plants, while \(\mathrm{T_{L,Rad}}\) was not sensitive to water changes in maize  
Figure 4: **(A) Seasonal average reflectance of soybean (blue continuous line) and maize (red dashed line) plants for the three water holding capacity (WHC) groups: Wet/control (100% WHC), Mid (70% WHC), and Dry (40% WHC) shown with different line thickness. Shaded area shows the 95% confidence intervals. (B) Zooming of region between 500 and 680 nm of (A). (C) Reflectance comparison between soybean (blue continuous line) and maize (red dashed line) for three days of measurement (DoM) shown with different line thickness. Shaded area shows the 95% confidence intervals. (D) Zooming of region between 500 and 680 nm of (C). **(Figure 5 and Table 4). T\({}_{\rm{L,Rad}}\) of both crops was also sensitive to phenology and its interaction with soil water stress (Table 4). Since the air temperature (T\({}_{\rm{air}}\)) was practically constant, \(\Delta\)T showed similar outcome to T\({}_{\rm{L,Rad}}\) for both crops (Figure S1 and Table 4). Mean differences due to soil drought for some VIs are displayed in Figure 5, while the rest are in Figure S1. VIs used to predict structural changes such as changes in LAI (e.g., NDVI, EVI, OSAVI, and REIP) were statistically significant between wet and dry soil water stratus for maize, but not for soybean. In addition, they changed significantly with phenology for both crops, with higher variation on maize as they showed notably higher F-values compared to other VIs (Table 4). rNDVI, a suitable index used to detect water stress [76], showed significant increase with soil drought (Figure 5). VIs used to detect concentrations of chlorophyll pigments (e.g., TCARI and R\({}_{\rm{(700)/670)}}\)), carotenoids (PSNDc), and anthocyanins (mARI), and VIs related to photochemical efficiency (e.g., sPRI and PRI\({}_{\rm{(570^{-}515)}}\)) significantly decreased with soil water stress in soybean plants (Figure 5 and Figure S1), whereas in maize they showed higher variability along time (Table 4). In addition, it is worth noticing that soybean R\({}_{\rm{(700)/670)}}\) and sPRI (calculated from 560 and 510 nm) did not significantly change over time (Table 4). Scatterplots shown in Figure 6 and Figure S4 between VIs with leaf physiology, h\({}_{\rm{c}}\) and chl can provide extra information about type of relation, the direction of change, linearity, and saturation of VIs. For instance, both crops presented weak positive linear relations (R\({}^{2}\) < 54%) between VIs with leaf A, T\({}_{\rm{r}}\), and g\({}_{\rm{s}}\) (Figure 6 and Figure S4) and negative relationships between \(\Delta\)T and leaf physiological parameters (Figure 6). \(\Delta\)T was not sensitive to changes in maize g\({}_{\rm{s}}\), T\({}_{\rm{r}}\), or A, while it was negatively correlated with soybean g\({}_{\rm{s}}\) and T\({}_{\rm{r}}\), with a relatively high correlation for g\({}_{\rm{s}}\) (R\({}^{2}\) = 0.47 and \(p\)-value \(<\) 0.001) (Figure 6). However, maize g\({}_{\rm{s}}\), T\({}_{\rm{r}}\), or A were sensitive to most VIs, but not for soybean.