26 



SOILS AND FERTILIZERS 



Table 6. — Percentage Composition op Residual and Glacial 

 Clays from Wisconsin 



It will be seen that of the substances important for their 

 plant-food value phosphoric acid and potash are somewhat 

 more abundant in the glacial soils, that lime and magnesia 

 are very much more abundant, while the less consequential 

 substances are present in large quantity in the residual soil. 

 This is because the residual soil has been subjected to more 

 leaching. 



28. JEolisLTi soils. — Following the retreat of the glaciers 

 there ensued a period of aridity, especially in the southwest 

 section of the territory now a part of the United States. Into 

 these regions there had been washed a large quantity of 

 fine glacial till, and during the dry period this was blown, 

 by high westerly winds, into a large area in the Mississippi 

 and Missouri valleys, where it is now found. It has been 

 given the name of loess and on account of its wide area and 

 great fertility it is an important agricultural soil. 



These soils are frequently of great depth, their texture 

 is favorable to the maintenance of good tilth and in prairie 

 regions their long period in grass, before they were placed 

 under cultivation, has given them a good supply of organic 

 matter. The following table contains a statement of 

 analysis of soils from different sections of the loessal area : 



