Value-added products as soil conditioners for sustainable agriculture

Due to the intensive use of fertilisers, soil degradation has become a global problem, leading to the depletion of organic matter and soil fertility. Meanwhile, the intensification of agriculture accompanied by urbanisation and industrialisation has drastically accelerated the waste generation rate. For instance, coal mining produces wastes in a large quantity globally, the majority of which end up in landfills or dump into storage dams. Accordingly, sustainable food production is driving global innovations to better utilise various waste materials to make value-added products, such as soil conditioners. Nowadays, soil conditioners are of great importance to improve plant growth and soil health and reduce chemical fertiliser use. This paper comprehensively reviews the soil conditioners derived from various agro-wastes and coal by-products. The process of producing soil conditioners and their sustainable applications in agriculture are also reviewed. Furthermore, sustainable approaches to recycle coal wastes are gaining increasing interest, and co-pelletisation of coal waste with agro-waste as a value-added soil conditioner to supplement soil nutrients in the agro-ecosystem has been proposed to improve the productivity of lands towards sustainable agricultural applications. This review highlights the possibility of turning coal wastes and organic wastes into revenue-earning products of environmental and economic values in the form of pellets for soil conditioning. But a multidisciplinary approach should be adopted to utilise the natural resources eco-friendly and cost-effectively, contributing to the United Nations Sustainable Development Goals.