Gypsum Amendment to Soil and Plants Affected by Sodic Alkaline Industrial Wastewater Irrigation in Urban Agriculture of Ouagadougou, Burkina Faso Juliane Dao & Désiré Jean-Pascal Lompo & Kathrin Stenchly & Volker Haering & Bernd Marschner & Andreas Buerkert Received: 28 June 2019 /Accepted: 16 October 2019 # Springer Nature Switzerland AG 2019 Abstract Low-quality water such as sodic alkaline in- dustrial wastewater is often used to irrigate crops of intensively managed urban gardening systems in the semi-arid tropics to help meet the fresh food demands of a rapidly increasing city population. An on-farm ex- periment was established to examine the effects of sodi- um (Na) and bicarbonate (HCO 3− )-loaded industrial wastewater on soil and crops on the one hand, and to determine melioration effects on soil condition and plant development on the other hand. To ameliorate the sodified soil, fine-powdered gypsum (CaSO 4 ) was ap- plied as soil amendment onto the upper soil (0–20 cm) before sowing of crops. Depending on soil pH and ex- changeable sodium percentage (ESP), which reflected the level of soil degradation (SDL), two different amounts of gypsum were applied: 6.8 t ha −1 in moderate and 10 t ha −1 in high SDL plots. Subsequently rainfed maize (Zea mays L.) and irrigated spinach (Spinacia oleracea L.) under two irrigation water qualities (clean and wastewater) were cultivated. Chemical and physical soil parameters, as well as plant root density (RLD), crop yield and concentrations of major plant nutrients and Na were determined. The results showed that gypsum appli- cation reduced soil pH on average below 8 and reduced ESP below 18%. Furthermore, gypsum-treated soils showed a significant reduction of sodium absorption rate (SAR) from 14.0 to 7.9 and aggregate stability was increased from 44.2 to 51.2%. This in return diminished Na concentration in plant tissues up to 80% and signifi- cantly increased RLD of maize. Overall, calcium (Ca) addition through the gypsum amendment changed the soil cation balance by increasing the Ca:Mg ratio from 3.5 to 7.8, which likely influenced the complex interac- tions between competing cations at the exchange surfaces of the soil and cation uptake by plant roots. Keywords Bicarbonate . Sodification . Soil amelioration . Spinacia oleracea . West Africa . Zea mays 1 Introduction West African cities are facing rapid urbanisation such as in Ouagadougou, the capital city of Burkina Faso. At an average annual growth rate of 9.2%, it reflects a likely doubling of the urban population of Burkina Faso by Water Air Soil Pollut (2019) 230:282 https://doi.org/10.1007/s11270-019-4311-x Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11270-019-4311-x ) contains supplementary material, which is available to authorized users. J. Dao : K. Stenchly (*) : A. Buerkert Organic Plant Production and Agroecosystems Research in the Tropics and Subtropics (OPATS), Universität Kassel, Steinstrasse 19, 37213 Witzenhausen, Germany e-mail: stenchly@uni-kassel.de D. J.<P. Lompo Institut de l’Environnement et de Recherches Agricoles (INERA), BP 8645, Ouagadougou 04, Burkina Faso D. J.<P. Lompo l’Institut des Sciences de l’Environnement et du Developement Rural (ISEDR), Université de Dédougou, Souri, Burkina Faso V. Haering : B. Marschner Department of Soil Science - Soil Ecology, Ruhr-Universität Bochum, Universitätsstrasse 150, 44801 Bochum, Germany