CLIMATIC CONTROL OF SOIL ACIDITY

A curve-fit model of the relationship between soil pH (A horizon) and climate forms the basis of a map of predicted pH for the conterminous United States. This map was produced with the aid of a large climatic data base, a computer mapping program and subroutines to map modeled values of soil pH. Patterns of pH follow well-recognized patterns of climate, although the pH of 7 line deviates greatly from Marbut's line dividing pedalfers from pedocals. The overall accuracy of the map and model was checked using a validation data set. Geographic patterns of pH are realistic, although land use, topography, and parent material may cause local variations about the predicted mean for a given region. Several apparently anamolous map patterns were also checked but found to be accurate. Prediction of the detailed pattern of pH will require variables in addition to climate.