Short-term influence of biochar on soil temperature, liquid moisture content and soybean growth in a seasonal frozen soil area

In the past decade, the application of biochar in agricultural soils has attracted wide attention. However, few studies have carefully explored the effects of biochar modification on plant leaf nutrients and the physiological process of plant leaves. To provide a better growing environment for crops and explore the best regulation mode of biochar in the farmland soil environment in the typical black loam area of Heilongjiang Province, through field experiments, we selected soybeans as the test crop and applied biochar in the soil. The agronomic characteristics and soil conditions of soybean plants were monitored by stage. The effects of different application methods and biochar gradients on the water and heat changes in soil tillage layers during different growth stages of crops were discussed, and the subtle differences of agronomic characteristics in different growth stages of crops were compared. The results showed that all kinds of biochar application modes could not change the general trend of water and heat change in soil tillage layer affected by environmental factors, and the effect of biochar application on soil liquid moisture content at 20 cm soil layer was not obvious. Biochar application can increase plant height and reduce stem diameter, but the effect is non-linear. The leaf nitrogen content (Leaf N-content) and leaf chlorophyll relative content (SPAD) were vertically distributed in the canopy, but they did not change significantly with the change of biochar application rate and mode. The application of biochar in autumn may bring crops into maturity earlier. Under the biochar application rate of 9 kg m−2, the mixed application in spring and autumn can bring the best biochar application effect.