438 Mineral Nutrition of Plants 



52,53). In other words, it is well established that when growth of plants 

 is limited by soil moisture supply, nitrogen tends to accumulate within 

 the plant because the rate of entry is approximately maintained in con- 

 junction with a decreased rate of utilization in growth processes; but 

 the general tendency for potassium content to be relatively low in plants 

 on the drier soils shows that rate of entry of potassium decreases to a 

 greater degree than does rate of utilization in these slower growing 

 plants. Hence, the availability of potassium to plants may be depressed 

 at the lower soil moisture contents, depending on the nature of the soil. 

 It is of interest to note, however, that Wimmer et al. (/j6) studied nu- 

 trient content of two varieties of sugar beets at different soil moisture 

 levels and reported that one variety showed the conventional decrease 

 in potassium content with decreasing moisture supply, whereas the 

 other variety showed the reverse trend under the same conditions. If 

 this observation is verified, it will indeed be a remarkable case of speci- 

 ficity in ionic entry between two varieties of a given crop. 



Although the phosphate ion may accumulate in plants limited in 

 growth by low soil moisture supply (84, 66) there is also evidence* that 

 plants so affected may have a relatively low content of phosphate (116, 

 117,40). Thus, the effect of soil moisture on phosphate nutrition is far 

 less consistent than that observed for nitrogen or potassium. This seems 

 to be indicative of the wide variation among soils in their fixing power 

 for phosphorus as conditioned by soil moisture content. Miller and 

 Duley (84) grew corn on a fertile silt loam from an alluvial bottom 

 along the Missouri River and, Janes' (66) bean plants were grown on 

 an Arredondo loamy sand fertilized with 1200 lb. per acre of 4—7—5. 

 These soils were conducive to phosphate accumulation under low mois- 

 ture supply. 



McMurtrey et al. (82) grew tobacco on a Colli ngton fine sandy loam 

 fertilized with 750 lb. per acre of 4-8-12 in the row, and found no effect 

 of soil moisture supply on phosphate content of tobacco leaves. Had- 

 dock* grew beets on a calcareous soil, Millville silt loam; Thomas et al. 

 (116) studied tomatoes presumably grown on a Hagerstown silty clay 

 loam that was variously fertilized. These two experiments yielded evi- 

 dence that the phosphate content of plants was reduced by diminishing 



*J. L. Haddock. Personal communication of an unpublished report. 



