Wadleigh and Richards 431 



the iron supply to plants on wet soils may be either hindered or ac- 

 centuated depending on the status of other prevailing conditions (pH, 

 carbon dioxide pressure), and the activity of iron in the soil appears to 

 affect the relative rate of entry of other plant nutrients into the roots. 



In light of the foregoing, it is of interest to consider the nutritional 

 disturbance known as "lime-induced chlorosis." There is a great deal 

 of evidence (25, 80, 54, 99, 1, 85, 34) that this type of chlorosis, which 

 is associated with a disturbance in iron metabolism within the plant, 

 is accentuated by wet weather or heavy irrigation and is ameliorated 

 when the soil dries. Wet, poorly aerated calcareous soils would be 

 conducive to accumulations of the bicarbonate ion, and it should be 

 recalled that Harley and Lindner (56) observed the development of 

 chlorosis on apple trees when irrigated with high bicarbonate water. 

 However, Reuther and Crawford (99) found no relationship between 

 the carbon dioxide content of the soil atmosphere and the degree of 

 chlorosis of grapefruit when the intensity of the symptoms varied with 

 soil moisture content over an irrigation cycle. Obviously, the primary 

 cause of chlorosis of plants growing on wet calcareous soils has not 

 been resolved, but a consideration of Halvorson's (55) theoretical 

 treatment along with manganese chemistry and HCO3 - activity might 

 prove fruitful. The status of both iron and manganese in the soil is 

 intimately related to the prevailing biological activity (55, 73). Hence, 

 the effect of a high level of soil moisture upon the prevailing micro- 

 organisms must be taken into account. As a case in point, Jones and 

 Tio (6y) observed that symptoms of frenching on tobacco associated 

 with low iron content of the plant could be eliminated by: (a) adding 

 ferrous sulfate to the soil, (b) maintaining a relatively low soil tem- 

 perature, or (c) by autoclaving the soil. The interrelationship between 

 iron availability to the plant and activity of microflora in the soil is 

 implicit in their findings. 



It is apparent, a priori, that wet, poorly drained soils are favorable 

 to the development of anaerobes and inhibitive to aerobes. Since the 

 anaerobes are capable of using oxygen that is in chemical combination 

 with soil components to meet the needs of their life processes, their 

 activity effects a reduction in iron, manganese, and other reducible 

 compounds (7^). It is also known that denitrification takes place rapidly 



