Water repellency prediction in high-organic Greenlandic soils: Comparing vis–NIRS to pedotransfer functions

Soil water repellency (SWR) is a common phenomenon across agricultural soils of South Greenland that can negatively affect soil functions. Existing methods to measure SWR as a function of water content (w) are laborious. This study was conducted to compare the potential of visible–near-infrared spectroscopy (vis–NIRS) as an alternative method to pedotransfer functions (PTFs) for predicting four SWR indices in 143 agricultural soils from South Greenland (clay, 0.016–0.172 kg kg^–1; organic carbon (OC), 0.009–0.241 kg kg^–1). Pedotransfer functions were established by multiple linear regression based on OC, clay, and pH. Partial least squares regression (PLS-R) and interval PLS-R were applied to build vis–NIRS prediction models (vis–NIR range 400–2,500 nm). The area under the SWR–w curve (SWR_area) and the critical soil water content (w_non) were accurately predicted by PTFs (R² =.90; R²_adj =.91) while the SWR after 60 °C pretreatment (SWR₆₀), and the integrative repellency dynamic index (IRDI) were predicted less accurately (R²_adj =.36; R²_adj =.27). Vis-NIRS models with variable selection performed at a better or close to the same level of accuracy as PTFs (SWR_area, R² =.88; w_non, R² =.90; SWR₆₀, R² =.63; IRDI, R² =.54). This study demonstrated vis–NIRS as a valuable alternative to PTFs for rapid assessment of SWR and as a tool for SWR mitigation for farmers in South Greenland. The results may well apply to other regions with similar texture and OC ranges, but further testing is required.