To the Editor.—
Ms. Silverglade comments on question 5 in my article, which was "There is no difference in food value between food grown in poor, worn-out soil and food grown in rich soil," and she gives the example of iodine. However, iodine is not needed by plants. The term "poor, worn-out soil" refers to the adequacy of soil for plant growth. Such soils produce very low yields, or even no crops at all. On the other hand, soils that are deficient in iodine, cobalt, or selenium grow luxuriant crops that are nutritionally deficient for animals. But these soils are not "worn-out" in the agronomic sense. Other soils may contain levels of molybdenum that are so high that crops grown on such soils are toxic for animals. And, actually, plants do not need soil at all; they can be grown in water solutions of chemicals by the "hydroponic" system.Ms.