428 Mineral Nutrition of Plants 



absorbing cells, which, in turn, is conditioned by the supply of oxygen. 

 Lawton {j2) grew corn plants on cultures of Clarion loam and Clyde 

 silt loam in which the moisture regime was maintained at near satura- 

 tion in some of the cultures and at or below field capacity in others. 

 The inferior corn plants produced by the soils maintained at near sat- 

 uration were found to have a relatively low percentage composition 

 of nitrogen, phosphorus, and potassium, but there was little consistent 

 effect on content of calcium and magnesium. 



Modified soil atmospheres resulting from excess soil moisture affect 

 the nutrition of plants not only through reduced oxygen supply but also 

 by increased partial pressure of carbon dioxide. Bradfield (18) has dis- 

 cussed the influence of increasing partial pressure of carbon dioxide 

 within a system containing calcium carbonate. In general, there is an 

 associated increase in activity of both hydrogen and calcium ions. It is 

 conceivable that these effects could markedly affect availability of cal- 

 cium and also other nutrient ions under certain soil conditions. In fact, 

 McGeorge and Breazeale (81, 21) conclude that a supply of carbon di- 

 oxide in the soil is the primary consideration in maintaining phosphate 

 availability in calcareous soils as a result of its modulating effect on 

 the high pH of these soils. On the other hand, Parker {93) found 

 that on a noncalcareous soil, Norfolk sandy loam, there was no con- 

 sistent effect on the calcium and phosphorus content of plants whether 

 the soil was fortified with carbon dioxide, the carbon dioxide removed, 

 or the soil left untreated. Chang and Loomis (28) have presented evi- 

 dence that increasing carbon dioxide content of the air-supplied nu- 

 trient cultures may be toxic per se to plants over and above any effect 

 of inadequacy in oxygen supply. Increasing partial carbon dioxide 

 pressure would effect an increase in bicarbonate ion concentration in 

 the aqueous phase. Harley and Lindner ($6) noted that when certain 

 apple and pear orchards in Wenatchee, Washington, were irrigated for 

 a number of years with water high in bicarbonate (200-360 p.p.m.), 

 they showed a marked decline in vigor and an increase in incidence of 

 chlorosis. A marked improvement was noted when irrigation water low 

 in bicarbonate was substituted for the high bicarbonate water. Calcium 

 carbonate concretions developed on the roots of the affected trees when 

 high bicarbonate water was applied to the calcareous soil present in that 



