104 SCIENCE AND SOIL 



Of course, these averages from the various Canadian provinces 

 must be considered as tentative and very preliminary, but they 

 must also be accepted as giving a reasonably correct general view 

 of the invoice of soil fertility in the most extensive types of soil 

 in those sections. Some other analyses made in part in connection 

 with special investigations are discussed in another place. 



REVIEW OF SOIL COMPOSITION 



A general summary of the mass of evidence contained in the 

 preceding pages concerning the composition of soils clearly sets 

 forth a number of definite and assured facts bearing significant rela- 

 tions to systems of permanent agriculture. One of these most 

 clearly established facts is that potassium as an element of plant 

 food belongs in the class with calcium and magnesium rather than 

 with phosphorus and nitrogen. In all normal soils the supply of 

 potassium is enormous. Thus, as an average of the Maryland soils 

 reported in Table 12, representing ten different geological forma- 

 tions, more or less abundant in most of the Atlantic states, we find 

 37,860 pounds of potassium and only 14,080 pounds of magnesium, 

 7840 pounds oL calcium, and noo -pounds of phosphorus, in 2 

 million pounds of soil. 



Measured by the total requirements of approximately maximum 

 crops in a rotation of wheat, com, oats, and clover (Table 13), the 

 potassium is sufficient for 473 years, the magnesium for 828 years, 

 and the calcium for 187 years; while the total phosphorus is suffi- 

 cient for the same crops for only 57 years. If we consider the plant 

 food removed in the grain alone, assuming that the coarse products 

 will remain on the farm, and also disregard the one abnormal mag- 

 nesium soil (from serpentine), the relative plant-food supply is 

 represented by 105 years for phosphorus, 3060 years for potassium, 

 2828 years for magnesium, and 6970 years for calcium. 



The complete analyses of the loess deposits at Dubuque, Iowa, 

 and Kansas City, Missouri, which contain only moderate amounts 

 of carbonates, show, as an average, 33,100 pounds of potassium, 

 13,400 pounds of magnesium, 23,500 pounds of calcium, and 1400 

 pounds of phosphorus, in 2 million of loess. 



In the following summary are reported the total phosphorus, 



