Russell Swift

and 25 more

Southern Africa is facing unprecedented strains on its agriculture, including a rapidly increasing population and demand for cereals. The global issues of climate change, water scarcity, and soil erosion are also affecting southern Africa, which expects a drier climate in the future. A promising tool in the fight for food security is Conservation Agriculture (CA), a technique based on minimum soil disturbance, mulching using crop residues, and crop rotation and/or intercrops. CA is promoted by organisations including the United Nations due to its potential to increase crop yields in arid/semi-arid climates; increase drought resilience; and increase infiltration of rainwater, reducing flooding and erosion. Despite its benefits and promotion, little is understood of the hydrodynamics of soils under CA cultivation. In order to investigate these hydrological processes, we installed Electrical Resistivity Tomography (ERT) monitoring systems (PRIME, developed by BGS) at three agricultural research sites in southern Africa (Zambia, Malawi, & Zimbabwe) under CA and conventional tillage systems. The sites are also instrumented with soil temperature, moisture, and matric potential sensors, as well as monitored groundwater boreholes, enabling comparison between monitoring techniques and the tracking of water from the ground surface to depth. ERT deployments for the respective sites include surface 2D, shallow cross-borehole 3D, and surface 3D electrode arrays. Each PRIME system is configured for twice daily data collection, and uses data telemetry for remote data retrieval. ERT monitoring allows us to monitor the hydrodynamics from the root zone, through the soil profile and vadose zone, to the aquifer. Initial results show variability between the sites, and heterogeneous nature of the vadose zone within the sites. This heterogeneity has been shown to influence preferential fluid flow pathways in the vadose zone. Monitoring over rainfall events has shown a strong, rapid response of pronounced, shallow wetting fronts, with limited changes at depth. We are beginning the process of comparing the hydrodynamics between CA and conventional plots, and the procedure of optimising data processing to enable better imaging of soil moisture changes at depth in the presence of rapid near surface changes.