Utilization of sewage sludge to manage saline–alkali soil and increase crop production: Is it safe or not?

Saline-alkali soil has become significant problem for global agriculture and food security as these soils have poor physicochemical conditions and reduce crop production by causing a wide range of physiological and biochemical changes in plants. More than 800 million hectares (Mha) of land throughout the world affected by saline-alkali soil, which accounts for 6% of the world total land area and about 62 Mha or 20% of the world’s irrigated land is affected by saline-alkali soil. Numerous studies on saline-alkali soils have been conducted throughout the years in an attempt to reduce plant productivity losses. Utilizing sewage sludge (SS) is an efficient way to improve saline-alkali soil and its physiochemical properties for plant productivity and improve soil’s health and crop yield. However, the in-depth mechanisms for the utilization of sewage sludge, their nutrient levels, toxic and harmful substances such as heavy metals, pathogenic microorganisms, antibiotics, and resistant genes that affect crop yield, groundwater quality, and ecological risks are still uncertain. This review enhances the awareness and knowledge to explore the sustainable mode of SS utilization in saline-alkali soil for the crop growth with crop rhizosphere effect, saline-alkali soil micro-ecology, carbon and nitrogen cycle enhancement. The potential future perspectives and research limitations for the utilization of SS for the crop production in saline-alkali soil are also discussed in review article.