The study looked at how different farming practices affect the amount of carbon in the soil in northern China. They tested different combinations of straw, chemical fertilizers, and organic manure on wheat and corn fields. The results showed that adding organic material to the soil increased the amount of carbon in the soil. Using only chemical fertilizers can reduce the activity of microbes in the soil, but adding organic material can counteract this effect. Combining crop straw with chemical fertilizers had a positive impact on soil carbon levels. Overall, returning corn straw and wheat straw to the field increased soil carbon more than just using wheat straw. Organic manure also had a significant effect on soil carbon levels.