The study looked at soil acidification in southern China's croplands under long-term fertilization. They found that paddy soils generally don't show much acidification, but there is significant acidification in paddy-upland rotations and red soils. The increase in chemical nitrogen fertilizers is the main cause of soil acidification. The rate of acidification slows down after 1-6 years of fertilization, but remains stable or slightly decreases after 7-10 years. Red soils with higher initial pH levels experience more significant acidification. To prevent further acidification, reducing the use of chemical nitrogen fertilizers is recommended for paddy-upland rotations and red soils.