Effects of different types of humic acid isolated from coal on soil NH3 volatilization and CO2 emissions

Abstract

Humic acid can improve soil nutrients and promote plant growth. Weathered coal and lignite can be used as agricultural resources due to high humic acid content, but their impact on soil NH₃ volatilization and CO₂ emissions are yet to be determined. In this study, a field experiment was carried out to compare the effects of four types of humic acid isolated from coal (pulverized weathered coal (HC), pulverized lignite (HL), alkalized weathered coal (AC) and alkalized lignite (AL)) on NH₃ volatilization, CO₂ emissions, pH, the C/N ratio and enzyme activities in soil cultivated with maize. The effect of biotechnology humic acids (BHA) was also examined for comparison. HL, AC, AL and BHA all increased cumulative NH₃ losses by 147.7, 278.5, 113.9, and 355.3%, respectively, compared with the control (chemical fertilizer only), and notably, BHA caused an increase of 90.71% compared with the humic acids isolated from coal. A significant increase in cumulative CO₂ losses was observed only under AL treatment, by 14.44-24.90% compared with all other treatments. Soil urease activity was positively correlated with cumulative NH₃ losses (P < 0.001), while the soil C/N ratio (P < 0.001) and soil sucrase activity (P < 0.05) were positively correlated with cumulative CO₂ losses. Since humic acid from pulverized weathered coal caused no increase in NH₃ volatilization or CO₂ emissions, it is therefore thought to be the most suitable humic acid for field application.

Keywords: Ammonia volatilization; Carbon emissions; Soil C/N ratio; Soil enzymes; Soil pH.