MINERALS IN NUTRITION 15 



Table 2. — Effect of Cations and Anions Added to Soil on the Intake 

 OF the Elements by Plants. 



Percentage increase over controls. (Minus sign indicates decrease) 



Experiment 5.— After the encouraging results of the preceding experiment, 

 it was decided to study the intake by plants of elements when added two 

 at a time to soil in quantities known to be excessive but not toxic. Four 

 elements, more or less similar and "higher up" in the electromotive series, 

 were used in the experiment: calcium, lithium, sodium, and potassium. 

 Lithium is not of nutritional or agricultural importance, but it was in- 

 cluded in the list because it possesses properties intermediate among the 

 elements used. Cabbage, celery, and lettuce were used as indicator crops. 



The work is incomplete, but indicates that when sodium and calcium 

 salts were applied together to soil, the calcium intake of the plants de- 

 creased. Similar results were obtained when potassium was added with 

 calcium, but the percentage intake of potassium increased. Plants could 

 tolerate lithium only in small quantities; but when potassium and lithium 

 were added together to soil, the intake of lithium was decreased. When 

 cabbage plants were grown in soil treatediwith both potassium and so- 

 dium, the potassium intake was definitely -tacreased. Apparently sodium 

 can replace potassium in plant nutrition. 



The results of these experiments indicate that it is possible to increase 

 the mineral content of some kinds of plants, the increase being dependent 

 on the crop, the mineral, and the other chemical substances present. It 

 seems probable that continued experimentation here and elsewhere may 

 develop procedures by which the mineral content of different food plants 

 may be controlled by cultural methods so that the minerals required by 

 man and animals may be adequately provided. 



