28 Mineral Nutrition of Plants 



more evaporation and transpiration and, hence, less leaching. Also, the 

 higher temperatures have favored hardwoods rather than conifers, and 

 this has further reduced leaching effects. As a result, the soils, being 

 less leached, are less podzolized and, therefore, better media for crop 

 growth. The fact that the parent rock material in the northern part of 

 the state has been sandstone and igneous rocks and in the southern 

 part largely limestone has also greatly favored the formation of better 

 soils in the latter area. 



If one goes south to humid semitropical or tropical regions, reddish 

 or lateritic soils are quite generally encountered. These soils are usually 

 low in organic matter and have generally suffered severe leaching. 

 They are, however, generally well drained and aerated and when 

 properly fertilized usually serve as excellent media for crop growth. 



Going west from Wisconsin, one encounters regions of less and less 

 precipitation. On reaching the subhumid region of the Dakotas where 

 the annual precipitation averages 20 to 25 inches, it is found that tall 

 grass vegetation has flourished instead of forest. Under these condi- 

 tions, the chernozem and related soils were formed. They are rich in 

 organic matter, have suffered little or no leaching, are rich in plant 

 nutrients, and in many respects represent our best media for crop 

 growth. The main failing is that the precipitation which accompanies 

 them is not at all dependable. Thus we see that the climate which 

 promotes the formation of the best soil media for crop growth usually 

 does not have sufficient precipitation for highest crop yields. 



To the west of the subhumid region of the Dakotas, one encounters 

 the semiarid region where the average annual precipitation is less 

 than 20 inches. Here, the limited soil moisture supply has restricted 

 vegetation to the extent that the soils formed are practically devoid 

 of organic matter. However, because of the virtual absence of leach- 

 ing, these soils are usually well supplied with available nutrients and 

 often make good media for crop growth when irrigated. Because of 

 little or no leaching, these soils are generally alkaline, frequently to 

 the extent of injury to crops. (See references 3, 4, 8, and 9 for further 

 details regarding origin and classification of soils and other pedologic 

 matters.) 



