8o 



Journal of Agricultural Research 



Vol. XVIII. No. a 



In this preliminary experiment the point to be emphasized is the 

 direct relation of nutrients to yield of both grain and straw when either 

 concentration or total supply is insufficient, and also the fact that the 

 total quantities of Ca, K, Mg, PO4, and N absorbed per plant vary 

 directly with the concentration and total supply of the nutrient solution 

 and in some cases are roughly proportional. The percentages on the 

 basis of dry weight are, on the whole, not very dissimilar. In the heads 

 the higher yielding plants show a lower percentage of some elements on 

 account of the production of a better filled grain. In the straw the per- 

 centage of K increases with increasing concentrations. 



It is of some interest to compare in each concentration the total 

 quantities of important elements found in the crop with the total quan- 

 tities added to the sand during the season. These figures are given in 

 Table II. 



Table II. — Percentage of absorption of total nutrients added to jars '^ 

 SAND CULTURES, SERIES I 



Concentration of solution (in p. p. tn.). 



200. . 



400. . 

 800. . 

 1,600. 



N. 



55 



72 



82 



103 



45 

 64 



75 

 96 



24 



35 

 36 

 49 



Ca. 



30 

 33 

 32 

 39 



Mg. 



27 

 29 

 28 



27 



o Calculations made on basis of total quantities contained in whole plants. 



It will be observed that somewhat similar percentages of Ca and Mg 

 were absorbed in each of the four different concentrations but that 

 higher percentages of K, PO4, and NO3 were absorbed from the higher 

 concentrations. In fact vv^ithin the limits of error all of the K and 

 NO3 were utilized by the plant. When these data are later considered 

 from a critical standpoint in connection with questions of supply and 

 concentration, it will become evident that the data for absorption do 

 not represent simply the influence of concentration. They may be 

 interpreted to mean that in the lower concentrations the total supply 

 was insufficient during the first part of the growth period, thus stunting 

 the plant in such a way that later additions of nutrients could not be 

 absorbed at a maximum rate, as they could be in the highest concentra- 

 tion. It should be stated finally that these sand cultures were placed 

 out of doors in good light, adjacent to crops grown in a number of dif- 

 ferent soils at the same time. In all these soils the crop yields were 

 much superior to those produced in the highest yielding sand culture. 

 Limitations in the nutrient media of the sand cultures must therefore 

 have existed and undoubtedly are to be ascribed to deficient total supply. 



