Temporal monitoring of the soybean cycle using Sentinel-2 images and NDVI analysis

Abstract. This study aims to monitor the temporal dynamics of soybean crop development using Sentinel-2 multispectral imagery and the Normalized Difference Vegetation Index (NDVI). Five image acquisition dates were selected to represent key phenological stages of the crop: emergence, early vegetative stage, flowering, pod formation, and maturation. NDVI maps and difference analyses between consecutive dates were employed to assess changes in vegetation vigor over time. The results showed characteristic pattern for irrigated soybean: NDVI values increased during early growth and peaked during flowering, followed by a gradual decline toward maturation, consistent with the typical spectral responses across crop phenological stages. The spatial resolution of the images allowed the identification of field-level variations, including planting row differences and the effects of machinery tracks on plant development. A key contribution of this study is the establishment of a reference multitemporal NDVI pattern for soybean under irrigated conditions. This reference can serve as a baseline for comparing non-irrigated fields, supporting the detection of anomalies caused by stress factors such as water scarcity, pests, or diseases. The method stands out for being low-cost, accessible, and user-friendly, which makes it valuable for both large-scale and smallholder farmers. Although NDVI is effective in identifying variations in plant vigor, it does not indicate the health loss of plants compared to a good health one and should be complemented with additional agronomic information. The approach presented here reinforces the potential of NDVI-based temporal analysis as a practical tool for crop monitoring and precision agriculture.