这可能有以下几方面的原因：一是施肥量大、肥力水平高的土壤，表层土壤养分

This may be due to the following reasons: First, the soil with a large amount of fertilization and a high level of fertility has a high nutrient content in the surface soil (Table 2), so the roots of rice are mostly distributed on the surface of the soil, and the roots are shallow, and the roots of rice are the earliest. Organs that perceive adversity stress (Liu Ying et al., 2003), rice plants no longer produce new roots after full earing (Jiang Baochun, 2017), and the frost resistance is weaker, while the soil with low fertilization and low soil fertility level, the surface layer The nutrient content of the soil is relatively low. In order to obtain the nutrients needed for its own growth, the rice root system penetrates deeper and wider, and the root system is relatively more frost-resistant when encountering chilling damage.

This may be due to the following reasons: First, soil with large amount of fertilization and high fertility level has high nutrient content in the surface soil (Table 2), so rice roots are mostly distributed in the surface of the soil, with shallow penetration, and the root system is the earliest organ of rice to sense adversity stress (Liu Ying et al, The nutrient content in the surface soil is relatively low. In order to obtain the nutrients required for its own growth, rice roots are planted deeper and wider, and their frost resistance is relatively stronger when encountering cold damage.

This may be due to the following reasons: First, the soil with a large amount of fertilization and high fertility level has a high nutrient content in the surface soil (Table 2), so rice roots are mostly distributed in the surface soil, and the roots are the earliest organs for rice to perceive adversity stress (Liu Ying et al., 2003). After full heading, rice plants no longer have new roots (Jiang Baochun, 2017), and their frost resistance is weaker, but the amount of fertilization is small.