Nitrogen-phosphorous-potassium (NPK) fertiliser dominates the market and the base chemical for nitrogen is ammonia. In Asia, ammonia is produced from hydrogen obtained from coal and subsequently combined with nitrogen, a by-product of oxygen separation. Ammonia may either be combined with carbon dioxide (CO2) to provide urea or converted to nitric acid which in turn is partially used to upgrade lignite at a significant scale.
However, the application of NPK fertiliser can cause nitrogen pollution, gaseous emissions of ammonia are a respiratory irritant, and nitration of water systems is associated with algal blooms; less than half of applied fertiliser nitrogen is absorbed by plants.
Lignite-based fertilisers are in development and gaining commercial success, especially with farmers who avoid applying NPK fertilisers. The largest commercial product is the conversion of lignite to potassium humates which also offer slow-release nitrogen. In newer technologies, ammonolysis converts lignite to a ‘peat’ like humate mineral, and biotreatments can extract a liquid humate fertiliser. This technology group offers more efficient use of chemical fertiliser.
Coal ash products also have a role in agriculture. Fly ash is deployed extensively in China and India; it can be beneficial in adjusting both chemical and physical soil properties. However, the ash-forming process concentrates metals and care must be taken to avoid biotoxicity by certain elements. Given appropriate safeguards agriculture offers an outlet for reclaimed ash pond wastes.
The study considers different solutions offered by coal and coal technologies, how they influence soil properties associated with erosion and desertification resistance, enhance carbon sink attributes and soil fertility. There is an established niche market for humic products, and low rank coal products can augment resources and offer a means to lower chemical fertiliser use.