## 4 Discussion
Therefore, intense Chlab absorption in the red band leads to saturation of red reflectance at lower Chlab concentrations, rendering NDVI less sensitive to Chlab fluctuations in moderate to high concentrations. This highlights a potential NDVI intrinsic limitation in detecting vegetation variations in pistachio tree orchards. Finally, it is worth noting that Figure 5 revealed clusters that distinguish between different treatments and geographical locations. The location of the plots demonstrated a pronounced influence on the differences observed between the variables. This suggests that environmental factors related to location, such as local climate, soil composition, or micro-environmental conditions, might have a more prominent role in shaping these characteristics in pistachio trees. This insight could be instrumental in future research and management strategies, underscoring the importance of considering the specific context of each location when managing pistachio cultivation. Contrastingly, at first sight, the PCA revealed that the irrigation treatments we applied did not significantly differentiate the data points representing individual pistachio trees in our study. However, in the biplot of Figure 6, a difference is observed in the treatment due to the irrigation applied in the \"Moraleja\" plot, but not in the \"La Seca\" plot, indicating that in the second orchard, the irrigation treatment did not have a substantial impact on the characteristics we measured. This difference could be attributed to various factors, such as variations in water supply between the plots or differences in tree age [64]. This finding suggests that increasing water supply beyond a certain threshold may not result in changes in VIs. Therefore, it emphasizes the importance of optimizing water resource management practices. In fact, irrigation doses had a negative influence on the quality and nutritional parameters of the nuts, which can be observed in aspects such as non-split nuts, caliber, calcium, magnesium, potassium, and protein, as well as various fatty acids, such as stearic and oleic. On the other hand, a positive influence was observed in the case of the percentage of split nuts, iron and carbohydrate content, and certain fatty acids, such as palmitoyl, linoleic, and linolenic (Figure 7). However, analyzing the interrelationship between factors unrelated to the VIs generated by remote sensing falls outside the scope of the current paper. The significance of this research is underscored by the fact that it represents the first established correlation between vegetation indices derived from UAV multispectral and thermal imagery and the crucial agronomic and quality parameters for pistachio cultivation. Furthermore, we found that this relationship exhibits variations throughout the year. As the quality of pistachios is notably impacted by harvest timing [2], remote sensing techniques that account for variations in VIs could aid in determining the optimal harvest time. Hence, further investigation is necessary to fully comprehend the intricate association with quality characteristics, as it appears to be more complex. Additionally, future research endeavors could greatly benefit from exploring the integration of multiple indices in time series analysis. This approach would facilitate a more comprehensive understanding of pistachio trees' yield and stress and the development of nut quality in agricultural settings.