Wad lei gh and Richards 437 



soil moisture supply within the available range, but any generalization 

 would be hazardous, considering the present state of our knowledge 

 of the subject. 



Nutrient accumulation in plants at 

 various levels of soil moisture supply 



It would be logical to conclude that under conditions of adequate 

 nutrient supply, plants that are limited in growth by a relatively low 

 level of soil moisture would have a higher content of mineral nutrients 

 than plants under comparable fertility but not limited in growth by 

 moisture supply. Miller and Duley (84) studied this relationship on 

 corn plants. The growth of corn at an "optimum" level of soil moisture 

 was greater than that of comparable plants in soil maintained at a 

 "minimum" level of soil moisture. The nitrogen, phosphorus, and 

 potassium content of the plants was appreciably higher under the "min- 

 imum" soil moisture level, but the reverse relationship was observed 

 for calcium. Emmert (40) found that the smaller tomato plants grown 

 with a relatively low soil moisture supply were higher in nitrogen and 

 potassium content and lower in phosphorus content than the larger 

 control plants grown at an optimum level of soil moisture. 



Many studies have provided evidence somewhat at variance with that 

 cited above. Haddock* found no consistent variation in nitrate content 

 in petioles of sugar beets subjected to wide differences in irrigation 

 regime. Learner et al.f found that alfalfa irrigated whenever the soil 

 moisture tension reached 0.4 atmosphere at the i-foot depth had a 

 slightly higher nitrogen content than comparable alfalfa on which irri- 

 gation was delayed until moisture tension reached 4.0 atmospheres at 

 the 1 -foot depth. The effect of soil moisture content on activity of 

 nodule bacteria may be involved here. Most experimental evidence 

 shows that for a given level of fertility, decreasing soil moisture supply 

 is associated with a definite increase in nitrogen content of the plant 

 tissue, a definite decrease in potassium content, and a variable effect 

 upon content of phosphorus, calcium, and magnesium (117,116,82,66, 



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 Personal communication of an unpublished report. 

 +R. W. Learner, S. R. Olsen, C. R. Domingo, and C. A. Larson. Personal com- 

 munication of an unpublished report. 



