The researchers studied how using different crops and fertilizers in crop rotation affects the microbes in black soil. They looked at the number of different types of bacteria and fungi in the soil when growing winter wheat after legume crops with different fertilizers. They found that using mineral fertilizers with legume predecessors increased the number of helpful bacteria in the soil. However, increasing nitrogen levels had a negative impact on soil microbes. Using alternative fertilizers also reduced the number of beneficial microbes in the soil. Overall, the type of crop and fertilizer used in crop rotation can significantly impact the microbial activity in the soil.