Impact of Biochar on Soil Bulk Density and Aggregates of Lou Soil

Abstract

The effect of biochar on the bulk density and aggregate stability of Lou soil was evaluated and compared after biochar was applied for 2 years and 5 years through a field-positioning experiment. Five biochar amounts were applied in this study, as follows:0 t·hm-2 (B0), 20 t·hm-2 (B20), 40 t·hm-2 (B40), 60 t·hm-2 (B60), and 80 t·hm-2 (B80). The biochar was produced by pyrolysis of stems and branches from fruit trees at the temperature of 450℃ with limited oxygen apply. At the beginning of the study, biochar was mixed thoroughly with the surface soil (0-20 cm). After 5 years, the soil bulk density and aggregate stability of 0-30 cm soil layers (0-10, 10-20, and 20-30 cm) were measured and compared with the results obtained after 2 years with the purpose of observing the long-term and persist effects of biochar application. The results showed that:① compared with the results after 2 years of application, the effect of biochar on the aggregates at depths of 0-10 cm and 10-20 cm after 5 years were less distinct, and the effect on soil aggregates at depths of 20-30 cm was significantly enhanced; ② compared with the 2 year application, the aggregate stability and the content of the>0.25 mm aggregate size fraction were significantly increased at 0-10 cm depths after 5 years of biochar application at a rate of 40 t·hm-2, while bulk density was significantly decreased; at 10-20 cm and 20-30 cm soil depths, the stability of aggregates and the content of the>0.25 mm aggregate size fraction was significantly increased, while the bulk density was significantly decreased after 5 years of biochar application at a rate of 60-80 t·hm-2;③ when the biochar application rate was 60 t·hm-2, the increase in soil organic carbon was the highest after 5 years. After biochar was applied for 5 years, its effect was more significant lower in the soil profile; the soil bulk density was significantly reduced, and aggregate stability and the content of>0.25 mm aggregates were significantly increased at depths of 20-30 cm. Based on a comprehensive evaluation of the improvement effects and economic benefits, the most suitable biochar application rate was found to be 40-60 t·hm-2. It was further concluded that the effect of biochar on soil aggregates was gradual and sustainable.