Improving Crop Yield and Water Productivity by Ecological Sanitation and Water Harvesting in South Africa Jafet C. M. Andersson, †,‡, * Alexander J. B. Zehnder, § Bernhard Wehrli, ‡,∥ Graham P. W. Jewitt, ⊥ Karim C. Abbaspour, † and Hong Yang † † Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dü bendorf, Switzerland ‡ Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, 8092 Zurich, Switzerland § Alberta Innovates − Energy and Environment Solutions, Edmonton, Alberta, Canada, and Nanyang Technological University (NTU), Singapore ∥ Eawag, Swiss Federal Institute of Aquatic Science and Technology, 6047 Kastanienbaum, Switzerland ⊥ School of Bioresources Engineering and Environmental Hydrology, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, South Africa * S Supporting Information ABSTRACT: This study quantifies the potential effects of a set of technologies to address water and fertility constraints in rain- fed smallholder agriculture in South Africa, namely in situ water harvesting (WH), external WH, and ecological sanitation (Ecosan, fertilization with human urine). We used the Soil and Water Assessment Tool to model spatiotemporally differentiated effects on maize yield, river flow, evaporation, and transpiration. Ecosan met some of the plant nitrogen demands, which significantly increased maize yields by 12% and transpiration by 2% on average across South Africa. In situ and external WH did not significantly affect the yield, transpiration or river flow on the South Africa scale. However, external WH more than doubled the yields for specific seasons and locations. WH particularly increased the lowest yields. Significant water and nutrient demands remained even with WH and Ecosan management. Additional fertility enhancements raised the yield levels but also the yield variability, whereas soil moisture enhancements improved the yield stability. Hence, coupled policies addressing both constraints will likely be most effective for improving food security. 1. INTRODUCTION How shall we make undernourishment history in a world of increasing human population, ecosystem degradation, and stress on water resources? 1 A number of strategies exists and contextual variability calls for tailored solutions. 2 Effective management of water and nutrients is often emphasized because of their key role in crop production and in biogeochemical cycles of the environment. 3 The challenges of undernourishment, poverty, sanitation and water scarcity converge in Sub-Saharan Africa, where livelihoods primarily depend on smallholder rain-fed farming. 4,5 High rainfall variability and low soil fertility are two critical challenges facing smallholder farmers in several parts of Sub- Saharan Africa (SSA). Lack of financial capacity typically constrains smallholder farmers from addressing the low soil fertility with conventional synthetic fertilizers. 6 A potential alternative is low-cost ecological sanitation (Ecosan): the recycling of nutrients from human excreta to agriculture. By turning waste into a resource, the Ecosan strategy aims to simultaneously improve sanitation, prevent pollution and enhance soil fertility. 7,8 One strategy to enhance the crop water availability, and thereby minimize the impact of dry-spells on smallholder food production, is to use water harvesting and conservation technologies (WH). 9 The principal hydrological functions of WH are to reduce surface runoff in favor of enhanced infiltration and soil moisture, and to reduce soil evaporation in favor of enhanced crop transpiration. 10 Agriculturally aimed WH can be classified as in situ WH and external WH. In situ WH refers to technologies that capture surface runoff and enhance infiltration on the agricultural fields themselves. External WH refers to technologies that capture runoff from uncultivated areas (e.g., roads and grasslands), store water in Received: November 9, 2012 Revised: March 2, 2013 Accepted: March 26, 2013 Published: March 26, 2013 Article pubs.acs.org/est © 2013 American Chemical Society 4341 dx.doi.org/10.1021/es304585p | Environ. Sci. Technol. 2013, 47, 4341−4348