Comparison of groundwater recharge under conservation agriculture and conventional practice

Up to 70% of the populations in the sub-Saharan countries of Malawi, Zambia and Zimbabwe rely on groundwater resources. Under the pressure of demand for agricultural production in already water scarce regions, and further threatened by drought events, it is important to effectively select agricultural practices that minimize negative effects on groundwater recharge and availability. Over the last two decades, conservation agriculture has been promoted by many sub-Saharan governments and NGOs as a tool to obtain reliable crop yields while increasing soil fertility. Key principles of conservation agriculture comprise minimum tillage and mulching, and previous studies indicate positive effects of these practices on soil moisture balance. However, only limited studies have been undertaken on the effects on groundwater recharge in general, and none of these in the sub-Saharan context. In this study, we introduce a plot-scale approach with a combination of different measurement techniques to identify differences in recharge patterns between sites under conventional and conservation agricultural practice. By combining these different methods, we want to answer the question if increased infiltration of water into the soil promotes recharge, or if improved water retention in the root zone of the soil increases losses in groundwater recharge in the sub-Saharan environment. The presented setup comprises three experimental sites in Zambia, Zimbabwe and Malawi on which both conventional and conservation agriculture is practiced. Each site is instrumented with soil moisture monitoring probes, automated pressure transducers to log groundwater level fluctuations over time, and time-lapse electrical-resistivity tomography equipment to track soil moisture changes. Environmental isotopes, residence time tracers (such as CFCs and SF6) and water chemistry will be analysed to estimate groundwater age and chemical signatures at different depths.