MODIFICATION OF SOIL TEXTURE 87 



These figures, and those published by a number of 

 other experimenters, clearly show the larger portion of the 

 phosphorus, calcium, magnesium and potassium in the 

 fine-textured classes in all kinds of soil. The absolute 

 amount of the food elements is also greatest in the fine 

 separates. It is shown that those soils which have 

 undergone the greatest weathering the coastal plain 

 soils are much the lowest in the food elements through- 

 out the different classes. On the other hand, glacial 

 soils are relatively rich in these food elements. There 

 is also much less difference in composition between 

 the clay and the sand particles in glacial soils, presumabty 

 because these soils have been formed largely by mechani- 

 cal processes, without much weathering or leaching. 

 The arid soils presented are not fully representative, 

 but they illustrate the high percentages of the food 

 elements in all the classes of particles, although the 

 same concentration in the fine particles is apparent. 



It is, therefore, concluded that clay particles are 

 relatively richer in food elements than sand particles. 

 But in glacial and arid soils, and to a degree in residual 

 soils, the sand particles are much richer in food elements 

 than they are in soils of water-deposition, such as the 

 coastal plain. 



32. Modification of soil texture. The only feasible 

 method of changing the texture of a soil is by adding 

 to it material of a different texture. Thus, the green- 

 house man considers the requirements of his crops, 

 and by mixture of fine and coarse material obtains the 

 texture which is necessary for their best development. 

 This is entirely practicable where only a small volume 



