Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee Long-term performance of flue gas desulfurization gypsum in a large-scale application in a saline-alkali wasteland in northwest China Yonggan Zhao a,b,c , Shujuan Wang a,b,c, ⁎ , Yan Li a,b,c , Jia Liu a,b,d , Yuqun Zhuo a,b,c , Wankuan Zhang d , Jing Wang e, ⁎⁎ , Lizhen Xu a,b a Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China, China b Beijing Engineering Research Center for Ecological Restoration and Carbon Fixation of Saline-alkaline and Desert Land, Beijing 100084, China c Key laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China d Tsinghua Agriculture Co., Ltd., Beijing 100084, China e Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China ARTICLE INFO Keywords: FGD gypsum Soil salinity Soil sodicity Heavy metals Saline-alkali soils ABSTRACT Flue gas desulfurization (FGD) gypsum has been used as an amendment to reduce soil salinization and alkali- nization worldwide. However, the effective and safe use of FGD gypsum in agricultural land is still debatable in some countries, although many studies have reported its beneficial effects on soil management. Therefore, a study was conducted on wasteland (600 ha) close to the Yellow River in Inner Mongolia, China. The main aim of this research was to evaluate the long-term effects of FGD gypsum application on soil salinity and sodicity, crop production and heavy metals in soils and crops. The results showed that soil pH and exchangeable sodium percentage (ESP) in topsoil (0–20 cm) decreased dramatically during the first year, while a substantial reduction of electrical conductivity (EC) occurred during the second year after FGD gypsum application. Four years later, the EC, pH and ESP levels in reclaimed soils were 58.3%, 92.2% and 95.2% lower, respectively, than those in the initial soils. In addition, the FGD gypsum application altered the major water-soluble ion composition of dis- solved salts, showing high Ca 2+ and SO 4 2- concentrations and low concentrations of HCO 3 - , CO 3 2- and other water-soluble ions. After reclamation, the crop yields gradually increased over time, and the sunflower and corn yields reached more than 90% of the levels of local production of these crops. Moreover, the heavy metal (Cd, As, Pb, Hg and Cr) contents of the FGD gypsum-reclaimed soils and crops was far lower than the established standards and below detectable limits. This study provides convincing evidence of the benefits of the large-scale use of FGD gypsum to reclaim saline-alkali soils. 1. Introduction Flue gas desulfurization (FGD) gypsum is a by-product of the wet FGD process of coal-fired power plants (Chen et al., 2001). Its main content is CaSO 4 or a mixture of CaSO 3 and CaSO 4 . To meet clean air standards, almost all coal-fired power plants are required to be equipped with a desulfurization facility to remove SO 2 from the flue gas (Wang et al., 2017). As a result, large amounts of FGD gypsum are being produced and stored in landfill plots and/or mountains (Clark et al., 2001). In China, for example, the annual production of FGD gypsum was 6.5 Mt in 2005 and increased to 75.5 Mt in 2013, according to the China Electricity Council (Pan et al., 2015). As regulations of SO 2 emissions limits become increasingly strict (SEPA, 1997), increasingly greater quantities of FGD gypsum will be produced in the future. This solid waste is able to create environmental problems and undesirable legacies for future generations (Clark et al., 2001). However, a rea- sonable utilization of FGD gypsum may shift the value of this waste material and harness and improve its surroundings (Wang et al., 2017). FGD gypsum can be used as a substitute for mined gypsum in many applications, e.g., construction, food and agriculture (Clark et al., 2001; Wang et al., 2008), due to its relatively high content of CaSO 4 and smaller particle size (Dontsova et al., 2005). Surveys conducted an- nually by the American Coal Ash Association on coal combustion pro- ducts and use showed that 60% of FGD gypsum was being used bene- ficially in 2008 (Baligar et al., 2011). In the US, approximately 98% of FGD gypsum was used in wallboard products for residential and com- mercial buildings, as an ingredient in Portland cement, and as a filler ingredient in some foods and toothpaste; in contrast, only https://doi.org/10.1016/j.agee.2018.01.009 Received 16 October 2017; Received in revised form 12 December 2017; Accepted 4 January 2018 ⁎ Corresponding author at: Address: No. 1 Tsinghua Yuan, Zhongguan Village, Haidian District, Beijing 100084, China. ⁎⁎ Corresponding author at: Address: No. 12 South Street, Zhongguan Village, Haidian District, Beijing 100081, China. E-mail addresses: wangshuj@tsinghua.edu.cn (S. Wang), wangjing02@caas.cn (J. Wang). Agriculture, Ecosystems and Environment 261 (2018) 115–124 Available online 24 April 2018 0167-8809/ © 2018 Elsevier B.V. All rights reserved. T