Fly ash in agriculture: A global perspective on utilization, benefits, and challenges

Fly ash (FA), a major byproduct of coal-fired power plants, has become a growing environmental concern due to its large-scale generation and underutilization. Globally, over 1 billion tonnes of fly ash are produced annually, with India alone generating near about 232 million tonnes, out of which only approx. 70% was utilized much of it still unused or landfilled. With rising energy demands and industrial activity, Fly ash management has emerged as a burning issue at the interface of waste disposal and sustainable agriculture. This review synthesizes global and regional data on FA generation, utilization patterns, and its agronomic potential. Scientific studies reveal that fly ash, when applied appropriately, can increase soil pH, improve nutrient availability (e.g., K, Ca, Mg, Zn), and enhance crop yield across a range of crops including rice, wheat, maize, and legumes. Experimental findings also indicate improvements in soil structure, organic matter content, and microbial biomass, particularly when FA is integrated with organic amendments like compost, vermicompost, and biochar. However, concerns over the presence of heavy metals such as arsenic, lead, and cadmium sometimes exceeding FAO and WHO permissible limits underscore the need for regulated application rates and long-term monitoring. The review highlights successful state-level applications in India and documents international case studies from China, USA, Poland, and Australia, where FA use has demonstrated both agronomic and environmental benefits. Despite this, barriers such as lack of awareness, inconsistent quality, absence of subsidies, and regulatory gaps continue to hinder widespread adoption. Cost-benefit analyses show that FA, when used as a partial fertilizer substitute, is economically viable, especially for acidic and marginal soils. This review identifies critical research gaps, including insufficient long-term field data, lack of standardized protocols, and limited farmer-centric extension models. It concludes with policy recommendations and best practices for promoting the safe, science-based, and integrated use of FA in agriculture, aligning with circular economy goals and the broader agenda of sustainable soil management and climate-resilient agriculture.