Wadleigh and Richards 429 



area. It is of interest to note that the chlorosis which develops under 

 these conditions is characterized by an abnormally high potassium and 

 low calcium content of the leaves (74). 



The evidence appears to indicate that relatively low concentrations 

 of carbon dioxide in the soil air of calcareous soils aid nutrient avail- 

 ability, but that the high carbon dioxide partial pressures which may 

 occur under excessive soil moisture may be deleterious to root activity 

 and nutrient entry. 



Excessive soil moisture may have an indirect effect on the supply of 

 nutrients to the plant. Oskamp and Batjer (92) observed in their studies 

 of soil conditions in relation to fruit growing in New York that the 

 most unfavorable orchard locations are those in which shallow rooting 

 occurs because of a high water table during certain seasons of the year. 

 Muller (86) also noted that claypan soils maintaining a high moisture 

 content of the subsoil restrict root development of guayule and may 

 even asphyxiate those roots which have penetrated the lower strata prior 

 to the prevalence of excess moisture. That is, shallow and restricted 

 root development means that a given plant has a correspondingly 

 smaller volume of soil to draw upon for nutrients. Furthermore, the 

 moisture reservoir available to the plant is also restricted so that the 

 plant may suffer from drought and be unable to utilize nutrients in 

 the fertile top soil, even though moisture is present in soil at depths 

 within the normal scope of root penetration of the species. Thus, par- 

 adoxically, the prevalence of excess moisture in the soil during the 

 early part of a growing season may seriously intensify the adverse effect 

 of drought later in the season. 



Under the anaerobic conditions which may prevail in wet, poorly 

 drained soils, there tends to be a decrease in the degree of oxidation of 

 both inorganic and organic constituents. Lawton (72) observed a 

 marked increase in the extractable ferrous iron content of Clarion 

 loam and Clyde silt loam when the soils were compacted or maintained 

 at high moisture content together with an associated decrease in extract- 

 able ferric iron. Anaerobic conditions resulting from waterlogging of 

 soil may also effect an increase (tremendous in some soils) in exchange- 

 able divalent manganese {112, 73). Studies by Fujimoto and Sherman 

 (4]) indicate that the effect of a level of soil moisture on manganese is 



