SOIL COMPOSITION 101 



From the general glacial map of the United States it will be 

 seen that southeastern Minnesota lies in the older lowan glaciation, 

 while most of the remainder of the state is covered by the late 

 Wisconsin glaciation. This may account for the marked difference 

 in potassium content between the soils of eastern and western 

 Minnesota. (See also Tables 15, 16, and 17 for a comparison of 

 these areas in Illinois.) It will be noted that the Red River basin 

 lies within the boundaries of the old glacial lake, " Agassiz." (See 

 also Canadian soils.) 



The analysis of a sample composed of equal parts of two hundred 

 representative soils from various parts of Minnesota showed 2360 

 pounds of acid-soluble phosphorus in 2 million of soil. 



The soils of the arid plains are, as a rule, rich in mineral plant food 

 and poor in nitrogen, doubtless due to the fact that with but little 

 rainfall there has been practically no loss of minerals by leaching, 

 and but small accumulation of vegetable matter, in which the 

 supply of nitrogen is contained. Headden (Colorado Bulletin 65) 

 reports ultimate analyses of four Colorado soils, showing as an aver- 

 age 2900 pounds of phosphorus and 39,500 pounds of potassium; 

 but the average of six soils shows only 2000 pounds of nitrogen, 

 in 2 million of surface soil. Widtsoe (Utah Bulletin 52) shows 37 

 analyses of Utah soils averaging 1850 pounds of acid-soluble phos- 

 phorus and 2450 pounds of total nitrogen, in 2 million of soil, in 

 the most fertile valleys. On the arid plains the supply of nitrogen 

 is usually very much less. Doctor Widtsoe states that he, " in 

 common with those who have traversed the wastes of western 

 America, has traveled for days without seeing a trace of vegeta- 

 tion, and such soils are almost devoid of organic matter and humus, 

 and contain but small quantities of nitrogen." Hilgard gives 600 

 pounds of total nitrogen and 2000 pounds of acid-soluble phosphorus 

 in 2 million of soil, as the average of 16 analyses of the arid soils of 

 Colorado. As a rule, the soils of the arid region contain about 3 

 per cent of lime (CaCO 3 ), or 30 tons of calcium carbonate in 2 

 million pounds of soil; and the Utah Station reports 18 soil analyses 

 from one county, containing as an average more than 20 per cent 



