The study looked at the properties of humus in high-yield fields in Shandong Province. They found that the amount of organic carbon and humic acid carbon in the soil was higher in high-yield fields compared to mid-low-yield fields. The ratio of humin acid carbon to fulvic acid carbon varied, with organic carbon being four times higher than humic acid carbon. The levels of available N,P, and K in the soil affected the composition of humus, with calcium carbonate and soil pH being the most important factors in determining the ratio of humin acid to fulvic acid.