LOSSES OF PLANT FOOD FROM PLANTS 555 



TABLE 115. PLANT FOOD REMOVED FROM PLANTS BY LEACHING WITH WATER 

 Percentage of Total 



and could not be removed by leaching, except in the case of the 

 dead-ripe wheat; while phosphorus as well as the other elements 

 was apparently taken up in excess of the absolute needs of the 

 plants and in part tolerated until removed by leaching. This is 

 the most probable explanation for the difference in results from 

 these experiments and those reported by Wilfarth, Romer, and 

 Wimmer; and the author has taken the liberty of suggesting to 

 Le Clerc and Breazeale that by extending these investigations in 

 connection with fertilizer experiments, results of great scientific 

 value and of far-reaching practical importance will probably be 

 secured in relation to the absolute requirements of plants for the 

 different elements essential to plant growth. It has long been 

 recognized that the analysis of the plant, or of the plant ash was 

 not a sufficient guide for use in planning systems of fertilization; 

 but, for certain of the elements, the analysis of the thoroughly 

 leached plant at the proper stage of growth may give more satis- 

 factory information; and, because of its very general character, 

 it seems especially appropriate that it should be continued by 

 the federal government, while local problems, such as county soil 

 surveys, are perhaps better managed by the state institutions. 



The fact that phosphorus is most frequently the limiting element 

 in plant growth or crop yield on most normal soils, especially for 

 legume crops, suggests that the averages commonly accepted for 

 the composition of crops probably represent the minimum amounts 

 of phosphorus, as a rule. 



