Abstract
(1) Soil surveys are classified into (i) preliminary reconnaissance surveys, (ii) broad ecological surveys, (iii) detailed physiological-ecological surveys, and (iv) special-purposes surveys. The objects of each are briefly discussed. (2) Particular consideration is given to the methods of physiological ecology, which attempt to assess the chief soil factors controlling plant growth. (3) Soil factors are grouped into (A) static factors, which do not fluctuate appreciably during a growing season, and (B) dynamic factors that may exhibit marked fluctuations within a season, or during years when climatic conditions vary.