Trends in the soil chemistry of South China since the 1930s

Chinese soil-profile data from the 1930s through the 1980s now permit preliminary statistical tests of broad hypotheses about degradation trends for soils of given site characteristics. Given a soil-history data set, the first challenge is to devise an algorithm to detect and correct possible sampling biases in the original source materials. The soil-profile data show that South China has not had a trend toward soil acidification, as some had feared in the 1930s. Acidity abated between the 1930s and the late 1950s, though part of this improvement was reversed in some areas after the 1950s. Nor is there a clear downtrend in nutrient content, though the regional patterns in south China's soil-nutrient trends demand an explanation. Total potassium rose throughout China. In the Southwest, there was an impressive rise after the 1950s in organic matter and total nitrogen, but not in phosphorus. The trends further east were different: slight declines in organic matter and N and a slight rise in P after the 1950s. The patterns correlate over time and space with differences in cropping intensity, which outweighed the accompanying differences in fertilizer application rates. Cropping intensity abated and soil nutrients rose between the 1930s and the late 1950s. Thereafter, the rise of multiple cropping and of yields was accompanied by a slight downtrend in soil nitrogen and organic matter-except, again, in the Southwest, where cropping was always less intense.