The study looked at how using Chinese milk vetch instead of some chemical fertilizers can help sustain crop yields and increase soil carbon in a double-rice system in China. They tested different levels of fertilizer and milk vetch over 10 years and found that using a mix of milk vetch and 80-100% of the recommended chemical fertilizer gave the best results, with higher yields and more soil carbon. Using only milk vetch or reducing chemical fertilizer too much lowered yields, but adding the right amount of milk vetch boosted soil carbon. This suggests that using milk vetch can help maintain crop productivity and soil health in this type of farming system.