Determinants of soil field-saturated hydraulic conductivity across sub-Saharan Africa: texture and beyond

Abstract

Soil infiltration is a critical hydrological process governing water security and related ecosystem services. The infiltration capacity of soils is largely controlled by their hydraulic conductivity. Hence, understanding soil hydraulic conductivity is critical for effective soil and water management. Despite recent efforts in assembling measurements of soil hydraulic conductivity, global databases and derived pedotransfer functions lack coverage in the tropics. Africa, in particular, remains sparsely represented in these global databases, and representative observations of soil hydraulic properties are few and of mixed form and quality. In this presentation, we introduce a new dataset of soil infiltration measurements and accompanying indicators of soil and land health collected systematically using the Land Degradation Surveillance Framework (LDSF) in 3573 plots from 83 100 km2 sites across 19 countries in sub-Saharan Africa and present the results from a recent study* where we used these data to (a) determine field-saturated hydraulic conductivity (Kfs) and (b) explore which variables best predict variation in Kfs. Our results show that sand content, soil organic carbon (SOC), and woody cover had a positive relationship with Kfs, whereas grazing intensity and soil pH had a negative relationship. Our findings highlight that, despite soil texture being important, structure also plays a critical role. These results suggest significant opportunities to improve soil hydrological functioning through management and restoration practices that protect and enhance soil structure. Enhancing SOC content, limiting livestock stocking rates, promoting vegetation cover, particularly woody vegetation, and preventing and halting soil erosion can increase Kfs. This evidence can guide sustainable land management practices and restoration interventions across the region for improved soil health and water security. Our dataset expands existing regional and global databases of soil hydraulic properties, improving coverage for Africa and providing field data for underrepresented land uses and soils. As such, we envision that this dataset can contribute to improved understanding and prediction of soil hydraulic properties and to improved Earth system and land surface models for applications in Africa.   * Bargués-Tobella, A., Winowiecki, L.A., Sheil, D., and Vågen, T.G. Determinants of soil field-saturated hydraulic conductivity across sub-Saharan Africa: texture and beyond. Water Resources Research. DOI 10.1029/2023WR035510. In-press.