Lysimeter Experiments 



55 



the drainage water. The average amounts of potassium removed annually 

 from the soil by drainage water during the five-years period, and by 

 crops during the first four years of the period, are given in table 40: 



TABLE 40. Potassium in Drainage Water and in Crops 

 (Pounds per acre, annual average) 



The striking feature of these figures, as compared with those shown 

 in the corresponding table for calcium, is the relatively small quantity 

 of potassium in the drainage water and the large quantity in the crops. 



Effect of plant growth on removal of potassium 



It will be remembered that the quantity of calcium in the drainage 

 water of the unplanted soil was greater than that in the drainage water 

 of the planted soil plus the calcium contained in the crops. So far as 

 potassium is concerned, the case is quite different, its total removal from 

 the planted soil being much larger than from the unplanted soil, as is 

 shown in table 41. Potassium differs in this respect not only from calcium 

 but also from all the other bases, altho to a less degree. This probably 

 explains why potassium is needed as a fertilizer for providing plant nutri- 

 ment, while the other bases are not required for the same purpose. 

 Evidently native potassium is not sufficiently soluble in the soil water 

 to supply the needs of the crops produced, as an average of only 61 pounds 

 of potassium was leached annually from an acre of unplanted soil to 

 offset the 79.2 pounds removed by the average crop from the same area, 



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