The study looked at how different types of soil react to acid rain. They tested three common types of soil and found that soil with more clay and cation exchange capacity (CEC) can resist acid rain better. The soil with the highest CEC and clay content was the most resistant, while the soil with the lowest CEC and clay content was the most affected by acid rain. The researchers also found that the critical pH threshold for acid rain varied between the different types of soil, with soil rich in clay and CEC having a higher threshold. This suggests that soil properties like CEC and clay content are important in protecting soil from acid rain.