Spectral Characterization of Soils Under Crop–Livestock–Forest Integration Using Portable NIR Technology

Agricultural and livestock management systems strongly influence soil attributes, soil organic matter dynamics, soil functions, and long-term sustainability. Thus, detecting variations in soil properties is essential for evaluating land-use systems. Rapid and cost-effective analytical approaches are increasingly required to monitor soil variability across management gradients. Near-infrared (NIR) spectroscopy is a repeatable, non-destructive technique that enables fast soil assessment with minimal sample preparation, making it suitable for field-scale evaluations. This study evaluated spectral measurements obtained with a portable BUCHI ProxiScout™ spectrometer (1350–2550 nm) from air dried fine soil samples collected at multiple soil depths (0 to 100 cm) under contrasting livestock management systems: extensive pasture, intensive pasture, integrated crop-livestock, integrated livestock-forest and integrated crop–livestock–forest. Spectral data were subjected to preprocessing procedures, including Savitzky–Golay smoothing, standard normal variate (SNV) correction, and first-derivative transformation. Principal component analysis (PCA) was used as an exploratory tool to access patterns and sample clustering. The results revealed spectral differentiation of management systems, demonstrating the sensitivity of NIR spectroscopy to land-use effects. The integrated crop–livestock–forest system showed the most distinct spectral pattern  among the systems. PCA loading analysis revealed contributions from spectral bands associated with soil organic matter, such as C–H and N–H bonds, and bands related to both soil organic matter and water, particularly O–H bonds. These findings indicate that portable NIR technology is a promising tool for expeditious, cost-effective, and low-residue discrimination of soil management conditions and supports efficient soil monitoring strategies. Acknowledgment: Fapesp (2023/02444-5 and 2025/06887-4).