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Monitoring of hydrodynamics under Conservation Agriculture in southern Africa using electrical resistivity imaging
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  • Russell Swift,
  • Jonathan Chambers,
  • Tongai Mtangadura,
  • Elijah Phiri,
  • Innocent Sandram,
  • Philip Meldrum,
  • Paul Wilkinson,
  • John Banda,
  • Joseph Chimungu,
  • Charles Chisanga,
  • Cornelia Inauen,
  • Ivy Ligowe,
  • Nellie Magwero,
  • Vengai Mbanyele,
  • Chawezi Miti,
  • Miyanda Moombe,
  • Patson Nalivata,
  • Pathias Lubinga,
  • Hatirarami Nezomba,
  • Keston Njira,
  • Willy Namaona,
  • Paul Mapfumo,
  • Florence Mtambanengwe,
  • Toga Mapangisana,
  • Frédéric Nguyen,
  • Murray Lark
Russell Swift
Université de Liège

Corresponding Author:[email protected]

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Jonathan Chambers
British Geological Survey
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Tongai Mtangadura
University of Zimbabwe
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Elijah Phiri
University of Zambia
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Innocent Sandram
Lilongwe University of Agriculture & Natural Resources
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Philip Meldrum
British Geological Survey
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Paul Wilkinson
British Geological Survey
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John Banda
University of Zambia
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Joseph Chimungu
Lilongwe University of Agriculture & Natural Resources
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Charles Chisanga
University of Zambia
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Cornelia Inauen
British Geological Survey
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Ivy Ligowe
Department of Agricultural Research Services (DARS)
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Nellie Magwero
Lilongwe University of Agriculture & Natural Resources
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Vengai Mbanyele
University of Zimbabwe
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Chawezi Miti
University of Zambia
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Miyanda Moombe
University of Zambia
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Patson Nalivata
Lilongwe University of Agriculture & Natural Resources
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Pathias Lubinga
University of Zambia
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Hatirarami Nezomba
University of Zimbabwe
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Keston Njira
Lilongwe University of Agriculture & Natural Resources
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Willy Namaona
Lilongwe University of Agriculture & Natural Resources
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Paul Mapfumo
University of Zimbabwe
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Florence Mtambanengwe
University of Zimbabwe
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Toga Mapangisana
University of Zimbabwe
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Frédéric Nguyen
Université de Liège
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Murray Lark
British Geological Survey
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Abstract

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.