The study analyzed soil samples from Northeast China to find a new indicator for soil fertility. They found that forest soil had more microbial biomass than maize and soybean soil. Microbial biomass was strongly linked to soil nutrients like organic matter, nitrogen, phosphorus, and potassium. Using microbial biomass carbon was better for evaluating soil fertility than microbial biomass nitrogen. This suggests that microbial biomass can be a useful indicator of soil fertility.