MINERALS IN NUTRITION 



13 



into four plots and treated as follows: Plot A, untreated control; Plot B, 

 magnesium added; Plot C, magnesium and calcium added; Plot D, calcium 

 added. Different crops were planted across these plots, and observations 

 were made as to the sensitivity of the different plants to magnesium de- 

 ficiency, and also as to the intake of calcium and magnesium with the 

 different treatments. On the basis of field observations alone, the apparent 

 tolerance of the crops to magnesium deficiency was as follows: 



Tolerant 



Not Tolerant 



Alfalfa Radishes Rape Peppers 



Rye Peas Sunflowers Buckwheat 



Beans Beets Cabbage Potatoes 



Soybeans Millet Corn Pumpkins 



Sudan grass Strawberries Cucumbers Rutabagas 



Swiss chard Sweet Potatoes Mangels Tobacco 



Lettuce Hollyhocks Watermelons Tomatoes 



Muskmelons Eggplant 



Table 1 shows the percentage intake of calcium and magnesium by 

 the plants, and the percentage increase or decrease of these substances 

 with reference to the several soil treatments. When only magnesium was 

 added, all of the plants increased in magnesium content, and seven of 

 the eleven decreased in calcium. When both calcium and magnesium were 

 added, peas decreased in magnesium, and corn and kale in calcium. When 

 calcium alone was added, five of the plants decreased in magnesium and 

 three in calcium. Experience has shown that magnesium is more easily 

 introduced into plant tissue than calcium when additional amounts of sub- 

 stances are added to soil. When magnesium and calcium are added to the 

 soil together, the intake of both may be decreased. 



Experiment 4. — It is known that if certain chemical elements are added to 

 the soil in abundance, they are taken in by some kinds of plants in amounts 

 larger than the normal growth and metabolism of the plants require. This 

 is sometimes referred to as "luxury consumption" of elements. Other 

 elements, however, will be taken into plants only in amounts needed. 

 In this experiment, lettuce and cabbage were grown for four successive 

 years on soil to which the cations (sodium, potassium, magnesium and 

 calcium) and anions (chloride, sulfate, and phosphate) were added sep- 

 arately to plots in quantities known to be far in excess of normal plant 

 requirements, but not in sufficient quantity to be toxic. The crops were 

 harvested and analyzed for the added chemicals. (Table 2.) 



Although the analyses varied somewhat from year to year, the results 

 showed that the intake of all cations was substantially increased, and 

 that the increases of magnesium and potassium were greater than those 

 of calcium and sodium. Thus, the first two would be much more nearly 

 in the "luxury consumption" class than the last two. Of the anions, phos- 

 phorus was increased to the greatest extent in the roots of plants. Per- 

 centage increases of chlorine were the highest of any of the elements 

 studied. Sulfur was increased substantially in both tops and roots of 

 lettuce plants, but not in cabbage. Cabbage is noted for its sulfur content; 

 but sulfur is not a "luxury consumption" element, and the cabbage takes 

 in only its normal amount regardless of the presence of an excess of the 

 element in the soil. 



