Does Complex Soil Enhance Grain Yield under Cropping System?

Global climate change and the increasing population have increased the difficulties associated with grain production. Several measures have been established to maintain a high crop yield, while preserving or increasing soil health, including biochar application to soil, and producing new complex soil with soil amendment application, e.g., biochar and soft rocks. However, previous studies have focused on the effect of complex soil on a single crop but have not considered crop rotation. In this study, field plots with foxtail millet cultivated for two years under biochar and soft rock application were selected for licorice cultivation to detect the effects of biochar and soft rock application on soil properties and licorice yield. The results showed that the biochar-treated plot had the highest licorice biomass (251.76 g/m2), followed by the combined biochar and soft rock treatment, and that the soft rock and control treatments had the lowest licorice biomass (97.65 g/m2). Plants in biochar-treated plots had the highest liquiritin and glycyrrhizic acid contents, followed by those under soft rock treatment. Soft rocks and biochar increased the soil catalase activity, organic matter, oxalic acid, tartaric acid, formic acid, and available phosphorus (AP). Correlation analysis showed that the licorice biomass was significantly positively correlated with oxalic acid and AP and negatively correlated with soil pH. AP was positively correlated with catalase activity and oxalic acid (p p < 0.05). Therefore, it can be concluded that the addition of biochar and soft rocks for two years could increase soil organic acid contents (especially that of oxalic acid), which function to reduce soil pH, increase soil AP content, and enhance licorice biomass