Changes in Soil Physicochemical Properties and Maize Production Following Improvement of Salt-Affected Soils Using Coal Bio-Briquette Ash in Northeast China

Soil degradation due to salinity and sodicity is one of the most important impediments to agricultural production. Coal bio-briquettes (CBB) made from coal, biomass, and desulfurizers have been proposed for use in desulfurization and usage of sustainable energy for coal and biomass in China. CBB ash contains calcium compounds such as calcium sulfate, calcium carbonate, and fly ash. The potential improvement of salt-affected soils using ashes from CBB made from two low-quality coals and/or organic manure (OM) was investigated in northeast China. The CBB ash application rates were 0 kg/m² (control), 1.16 kg/m², 2.32 kg/m², 4.64 kg/m², and 6.96 kg/m². Following the application of CBB ash and/or co-application of OM, maize production increased significantly, compared to control plots. Moreover, co-application with OM resulted in higher maize production than application of CBB ash only. Soil pH, sodium adsorption ratio (SAR), exchangeable sodium percentage (ESP), and Na⁺, HCO₃⁻, and CO₃²⁻ concentrations decreased, and Ca²⁺, Mg²⁺, and SO₄²⁻ concentrations increased from the start of the experiment to harvesting time. Maize production showed a tendency to increase with increasing CBB ash/OM application rates. The decrease in pH, ESP, and HCO₃⁻, and increase in Ca²⁺ in the application plots over time was particularly remarkable. Moreover, saturated hydraulic conductivity (K_s) after CBB ash application in the slightly and moderately salt-affected soils increased with increasing application rates. In case of the highest application rate (6.96 kg/m²), using ash from CBB made from lower quality coal, pH and ESP decreased from 9.47 to 7.61, and from 7.0% to 0.98%, respectively, and K_s increased drastically by three orders of magnitude. Therefore, not only soil chemical properties, but also K_s, were improved in salt-affected soils using CBB ash. In addition, the heavy metal content in CBB ashes was below the standard values according to Chinese guidelines. Taken together, these results demonstrate the feasibility of sustainable methods for energy usage and environmental application in China.