4.2.2. Effect of biochar as a soil amendment on soil quality
The results of soil analysis before the field experiment and after harvest are shown in Table
7. Before the experiments, the range of soil properties in the 9-treatment fields were
3.2~4.7% for soil organic matter, 5.2~6.0 for soil pH, 12~27 mg/kg for available
phosphorus P1 and 14~43 mg/kg for P2, 19~75 mg/kg for nitrogen as nitrate, and 15.4~20.8
meq/100 g for CEC. After harvest, the soil organic matter, soil pH, available phosphorus
P1 and P2, and CEC generally increased in the field plots treated with biochar. The increase
in soil organic matter and CEC showed that fairly large amounts of carbon and
exchangeable cations were introduced by biochar application. The high level of available
phosphorus P1 and P2 after biochar application indicated that the use of biochar as a soil
amendment led to a high retention of nutrients in the soil. By contrast, the contents of
nitrate-N in these biochar-amended plots were significantly reduced even when undergoing
nitrogen fertilizer application (Table 7). This further confirms that biochar can sorb
nitrogen fertilizers and inhibit their nitrification and thus the concentrations of nitrate in the
fields with biochar addition were largely decreased. In addition, soil analysis after harvest
revealed that soil organic matter, soil pH, available phosphorus P1 and P2, and CEC were
generally higher after the application of biochar and fertilizer than after the application of
fertilizer only (Table 7). Therefore, biochar as a soil amendment can improve soil quality
by increasing soil organic matter, pH, and CEC, and holding nutrients in soils.