COMPOSITION OF TYPICAL SOILS 79 



like amount of potash which is present mainly in the 

 sand. Because a soil has a given composition, it does 

 not follow that all of the different grades of particles 

 have the same composition. In fact the different 

 grades of soil particles in one soil may have as varied 

 a composition as is met with among different soils. 26 



The figures under i in the table give the composi- 

 tion of the particles, while under 2 are given the re- 

 sults calculated on the basis of the total amount of 

 each element. For example, the clay contains 1.47 

 per cent, of potash, while 50.8 per cent, of the total 

 potash of the soil is in the clay particles. 



A soil may contain a comparatively low per cent, of 

 potash or phosphoric acid, mainly in the finer particles 

 and evenly distributed so that the crop is better sup- 

 plied with food than if more were present in the 

 larger particles, unevenly distributed. The distribu- 

 tion of the plant food in the soil has not been so ex- 

 tensively studied as the question of total plant food. 

 The distribution of plant food in both surface soil and 

 subsoil, as well as in the various grades of soil parti- 

 cles, is an important factor of fertility. 



96. Composition of Typical Soils. A few exam- 

 ples are given, in tabular form, of the chemical com- 

 position of soils from different regions in the United 

 States. On account of variations in the same locality, 

 the figures represent the composition of only limited 

 areas of soils. There have been made in the United 

 States a large number of soil analyses, which as yet 

 have not been compiled nor studied in a systematic 

 way. 



