Effects of different biochar application methods on soybean growth indicator variability in a seasonally frozen soil area

Abstract

As an emerging soil amendment, biochar has attracted widespread attention worldwide. However, comprehensive research on the hydrothermal changes in biochar during natural freezing and thawing and the growth of crops after freezing and thawing has not yet been performed. The purpose of this study was to investigate the hydrothermal changes in biochar during freeze-thaw conditions and the variation in plant indicators in different biochar addition plots. Soybean was selected as the test crop via field experimentation. Biochar was applied to the soil at an areal density of 9 kg/m2 in autumn, spring, autumn and spring mixed application to identify whether biochar could be widely beneficial. The results showed that after natural freezing and thawing, biochar could provide a good accumulated temperature for crop growth before sowing and effectively improve soil moisture, causing the soil in the root zone of each study site to change slightly. At the same time, biochar application promotes crop growth; however, the effects of different application methods vary. Compared with the control case, in the case of spring biochar application, the plant height and leaf area increased by 20% and 6.3%, respectively, while the stem diameter decreased by 6.1%. The leaf nitrogen content and leaf chlorophyll content basically remained the same. In addition, in the case of multiple biochar applications, we found that the difference between soybean stem diameter and leaf area was the greatest of all the application modes. In the case of application in spring and autumn mixed, the differences in the soybean indicators within the same experimental plot were the greatest. Compared with the control results, the autocorrelation of application in spring and autumn mixed is weak and does not affect actual production. Therefore, the difference caused by biochar application can be approximately ignored.