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

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.

Phytoremediation potential of wheat intercropped with different densities of Sedum plumbizincicola in soil contaminated with cadmium and zinc.

Intercropping technology is applied widely in crop cultivation to help remediate soil polluted with heavy metals. To investigate the feasibility and potential of intercropping hyperaccumulator plants with crops in cadmium (Cd)- and zinc (Zn)-contaminated soil, a pot experiment was conducted to examine plant growth and the contents of Cd and Zn in the soil following intercropping of wheat and Sedum plumbizincicola. Five treatments were examined: control (wheat monoculture: 36 seedlings per pot), and intercropping of wheat with different planting densities of S. plumbizincicola (3, 6, 9 and 15 seedlings per pot, respectively). Results showed a decrease in soil pH, and in soil and wheat contents of Cd and Zn with increasing planting density of S. plumbizincicola, while the removal rate of Cd and Zn increased. Meanwhile, excessive planting (15 seedlings per pot) inhibited wheat growth by 27.34% compared with the control, and overall, the optimal planting density was 9 seedlings per pot, resulting in effective remediation with only a moderate effect on wheat growth. These findings highlight the value of intercropping S. plumbizincicola with wheat as a means of improving remediation of soil contaminated with heavy metals (Cd and Zn).