Use of satellite imagery for crop water status monitoring: a case study on soybean with Planet and Sentinel-2 satellites

This study evaluates the use of satellite data to monitor soybean water status under different irrigation regimes - Full irrigation (FI) and Regulated Deficit Irrigation (RDI) – across varying climate conditions of 2022 and 2023. Three key objectives guided this research: (1) assessing the potential of vegetation indices (NDVI, GNDVI, ENDVI, NDRE, and LAI) in providing real-time insights into crop health and irrigation needs; (2) comparing high-resolution PlanetScope (3 m, daily revisit time) imagery with Sentinel (10 m, 5 days) data for agricultural monitoring; and (3) examining the trade-offs between water savings and crop performance under FI and RDI strategies. Planet vegetation indices (VIs) respond promptly to changes in water availability, capturing the immediate effects of irrigation and rainfall on plant physiological processes and effectively tracking stress conditions, reflecting the in-situ physiological data (stomatal conductance , transpiration , leaf temperature ) measured with porometer/fluorometer LI-600. Comparative analysis between PlanetScope and Sentinel imagery found PlanetScope’s high resolution advantageous, but Sentinel provided highly correlated results although underestimations in most indices, suggesting it can be a cost-effective alternative for large-scale agricultural monitoring, but less trustworthy for precision agriculture purposes. The comparison between FI and RDI revealed that RDI, particularly in soils with higher water-holding capacity, can maintain crop yields with reduced water input, offering a sustainable alternative to FI without significantly compromising crop performance. This research concludes that RDI presents a viable strategy for water-scarce regions, providing significant water savings without drastically affecting crop productivity. Furthermore, remote sensing technologies offer practical, accessible tools for global irrigation management, supporting the sustainable intensification of agriculture in the face of climate change and resource limitations.