90 SCIENCE AND SOIL 



Bulletin 82) shows five important soil areas in Iowa, which closely 

 resemble similar areas in Illinois. 



(1) About one tier of counties bordering the Mississippi (with a 

 western projection which includes most of Cedar, Johnson, Iowa, 

 Poweshiek, and Jasper counties) is termed the Mississippi loess 

 area, and resembles the loessial soil on the Illinois side. 



(2) Similarly, along the Missouri and Big Sioux rivers the two 

 western tiers of counties are chiefly in the Missouri loess area. 



(3) The Kansan glaciation (overlaid with shallow loess on the 

 less rolling lands) covers the southern third of the remainder of 

 Iowa, and this resembles closely the lower Illinoisan, except that 

 the older Kansan is more broken and has much more exposed 

 till on the eroded hillsides. 



(4) The eastern part of the remainder of the state is covered by 

 the lowan glaciation, and (5) the somewhat larger western part 

 by the Wisconsin glaciation, both of which are also found in Illi- 

 nois. In both states the lowan glaciation is characterized by its 

 rolling topography and perfect surface drainage, and the Wiscon- 

 sin by its level prairies which require much artificial drainage by 

 tile and open ditches. 



Eight analyses of lowan soils, reported to the author by Doctor 

 J. B. Weems while professor of agricultural chemistry in the Iowa 

 State College, showed 900 pounds of acid-soluble phosphorus in 

 2 million of soil, as a general average. The several soil types repre- 

 sented varied considerably, however, as would be expected from 

 comparison with similar Illinois soils, the highest amount reported 

 being 1600 pounds of acid-soluble phosphorus per acre in a 6f-inch 

 stratum, corresponding to 1880 pounds of total phosphorus, if 

 85 per cent were acid-soluble. (This method of estimating total 

 phosphorus from the acid-soluble phosphorus is never safe for 

 application to individual soil samples, but it is approximately cor- 

 rect for large averages of most common soils of central United 

 States.) The acid-soluble potassium (which varies from less than 

 one sixth of the total in old soils to more than one third of the total 

 in more recent, less weathered soils) amounted to 4670 pounds as an 

 average of the eight soils (the highest being 7800 pounds) in 2 mil- 

 lion of surface soil, corresponding probably to 30,000 to 40,000 

 pounds of total potassium. The analysis of loess from Dubuque, 



