Comportamento espectral da cultura da soja em diferentes estágios de desenvolvimento

Abstract

The soybean crop plays an important role in Brazilian and world agriculture, being the most produced grain in Brazil and contributing significantly to rural income. Technological advances in the agricultural sector, together with the use of remote sensing (SR), have optimized grain production and quality, increasing international competitiveness. NDVI (Normalized Difference Vegetation Index) and NDRE (Normalized Difference Red Edge) are vegetative indexes obtained by SR that provide valuable information about crops. The objective of this work was to evaluate the spectral behavior of soybean crops at different stages of development using the NDVI and NDRE vegetation indexes and the spectral bands that compose them. The research was carried out in a 37-hectare area in Dourados, MS, Brazil, during the 2022/2023 harvest. Using the PlanetScope imager, images were collected at 15-day intervals throughout the crop cycle. The results showed that the average NDVI and NDRE values varied ccording to soybean development. NDVI performed better during crop development, while NDRE proved to be more sensitive during the soybean's maturation phase. The spectral data indicated a good and uniform development of the plot under study. In the red range, reflectance was low from the start of cultivation, decreasing further as the phenological stages progressed. In the red edge region, reflectance was slightly higher in the early and late stages of the cycle, with lower values in the periods of maximum vegetative development. The opposite behavior occurred in the near infrared, with higher reflectance, especially in the middle of the cycle. The NDVI and NDRE vegetation indexes showed lower values at the beginning and end of the cycle, with values increasing as the crop developed. Low variability was observed in the plot, with coefficient of variation values below 10%.