Estimating Nitrogen and Biomass Interactions as an Indicator of Forage Condition in Rangelands with Remote Sensing-Derived Variables

Forage nitrogen (N) and biomass measure rangeland quality and quantity. The N and biomass interactions (N*Biomass) are critical in understanding rangeland conditions, especially when deriving grazing or browse-carrying capacity indicators. Conventional methods have been used to measure N and biomass; their main shortcoming is labour intensiveness and time-consuming, especially when covering larger areas. Using remote sensing, limited studies focused on estimating the N*Biomass in the context of understanding rangeland conditions. This study, however, provides significant insights. It aims to understand the N*Biomass using vegetation indices and spectral bands in the Golden Gate National Park, South Africa. Stepwise Multiple Linear Regression (SMLR) and Random Forest modelling were performed to develop N*Biomass predictive models based on vegetation indices such as leaf area index (LAI), canopy chlorophyll content, and Sentinel-2’s spectral bands. The parsimonious SMLR model consisted of four variables, including LAI, spectral band 2 (Blue), 4 (Red) and 8a (Vegetation Red Edge), explaining 63% of N*biomass, whilst RF explained 41%. The study's findings indicate that the N*Biomass is explained by variables associated with the structure and the quality of the vegetation, providing valuable insights for future research and practical applications.