Moisture-dependent Water Repellency of Greenlandic Cultivated Soils

Abstract

The rapid warming of the Arctic is changing the conditions for agricultural activity in southwest Greenland markedly, which necessitates studies of the physical properties of the soil resource. Soil water repellency (SWR) is a soil property that changes soil functional behaviour across a soil-specific range in water-content (W). Although SWR occurs worldwide, it has not been studied in sub-arctic pasture and grass fields. Thus, the aim was to examine the prevalence of SWR in South Greenland and to establish pedotransfer functions for SWR on soil properties that are faster to measure than SWR, i.e. soil organic fractions, texture and soil water retention. This study included 145 soil samples from 22 sub-arctic agricultural fields distributed across three areas of South Greenland, with broad distributions in texture (clay: 0.017–0.194 kg kg−1) and organic carbon (OC) (0.009–0.241 kg kg−1) contents. The degree of soil water repellency (SWR) as a function of water content (SWR-W curve) was measured from oven-dry conditions to the water-content at which the soil became hydrophilic (WNON), and total SWR (SWRAREA) was calculated as the integrated trapezoidal area (SWRAREA) of the SWR-W curve. A total of 99% and 98% of the soil samples were water-repellent and extremely water repellent at their maximum SWR, respectively. Among the three soil organic fractions (OC, Loss-on-ignition at 550 °C, and 225 °C (LOI550 and LOI225)), LOI550 was the best predictor of SWRAREA and WNON (both with r2 = 0.93). Multiple linear regressions including clay content increased r2adj to 0.92 and 0.95 with OC and LOI550, respectively. The Campbell-Shiozawa (CS) model was fitted to the soil–water retention curves (pF 3.0–6.9), and the inverse slope (−α−1) of the CS model exhibited a high correlation to both SWRAREA (r2adj of 0.87) and WNON (r2adj of 0.93), thus suggesting that soil water retention governs SWR. Lastly, it was shown that the coefficient of proportionality between OC and both SWRAREA and WNON for these sub-arctic soils coincided with pasture soils from New Zealand.