104 



with soil ciiUurcs would parallel the results obtained 

 with solution eultures. It is well known that for many 

 organic substances, the powers of absori)tion and ad- 

 sorption possessed by soil are high; it is also well known 

 that in unsterilized soil numerous complex chemical 

 and biochemical reactions may occur, while such re- 

 actions in solutions, are largely absent and occur slow- 

 ly when at all. It seemed logical, therefore, to expect 

 dififerences between the results obtained bv the two 

 methods, because of the greater absorptive, chemical, 

 and biochemical action of soil. 



In order to make such comj)arisons, the writer plan- 

 ned a scries of experiments in the fall of 1913, and 

 had the experiments conducted by a number of stu- 

 dentvS, who used the data so obtained as a thesis for the 

 B. S. degree. The results so obtained are incorporated 

 in this publication, together with data subsequently 

 obtained by the writer. The data obtained from the 

 solution culture work were parallel with those reported 

 by the Bureau of Soils, and were discontinued after 

 the tirst set of trials was completed; however, the re- 

 sults of the soil culture experiments did not accord 

 with those of the solution cultures. For this reason 

 all of our later work was done with soil as the medium 

 in which the ])lants were grown. 



The Methods I'sed. 



All of the data given were obtained from experiments 

 conducted in the greeidiouse, the plants being grown 

 in either 2-gallon or 4-gallon pots. In all cases where 

 the 2-gallon pots were used, each pot contained 20 

 pounds of air dry, screened soil; while the 1-gaIlon pots 

 contained 10 pounds of air dry, screened soil. The 

 special treatments, as well as the fertilizer treatments, 

 were apjjlied as follows: about an inch of soil was re- 

 moved from the ])ot to be treated, and the nuit(>rials 

 added; then the soil in the ])ols was well stirred so as 

 to thoroughly mix the added materials with the ui)])er 

 half of the soil in the pots. After this mixing, the 

 soil that had been removed was returned to the pot. 

 The sj)ecial substances or compounds were usuallv 

 added at the rates of 100, 250, .lOO, and 1000 parts ])er 

 million of dry soil. In the later work, the smaller 

 ratios were omitted, since the apj)arent effects of the 

 small (juanlities were rather slighl. 



Based on the 10 i)oun(ls of soil per large pot, 18 grams 



