SOU, ANALYSIS AND INVESTIGATION II 



to simulate the properties of plant sap in some of these solvents 

 are obviously illogical, for the plant sap does not come in con- 

 tact with the soil grains, except through an accidental destruc- 

 tion of the plant. 



Naturally, comparisons were attempted between the amounts 

 of the mineral constituents extracted from a soil by these vari- 

 ous solvents and the amounts taken up by crops growing on the 

 soil. It was found, however, that the amount of any given 

 mineral constituent extracted from the soil by a solvent is not, 

 generally, the same as that taken up by the plant. Moreover, 

 the ratio of one constituent to another in the extract bears no 

 definite relation to the ratio of these constituents in the plant. 

 Nevertheless many efforts were made to establish "factors." 

 For instance, the percentage of potash extracted from the soil of 

 a field by hydrochloric acid is some multiple of the percentage 

 removed by a wheat crop ; it was sought to determine this multi- 

 ple, assuming it to be a definite ratio and a natural constant, and 

 it was designated as the potash factor. But there is a different 

 factor for phosphorus, another for calcium, and still others for 

 each and every constituent. The factors found for a soil from 

 one area generally do not hold for a soil from another area. 

 Again, different factors obviously must be used for different 

 crops. And, finally, the whole scheme becomes hopeless when it 

 is realized that the same crop will yield widely varying ash 

 analyses, depending upon the cultural methods employed, the 

 judicious selection of seed, the amount and distribution of rain- 

 fall and sunlight, and possibly other agencies, all of which affect 

 the growth and absorptive functions of the plant to as great an 

 extent as does the particular soil upon which it may be growing. 



Moreover, from the purely analytical point of view the situa- 

 tion is no better. For instance, the addition of potassium in the 

 amounts usually employed in ordinary fertilizer practice general- 

 ly does produce a noticeable effect on the yield of crop. The 

 average application of potash (K 2 O) is certainly less than 50 

 Ibs. to the acre. It is customary to consider the surface foot 

 of soil as the region affected by the fertilizer, and an acre foot 

 in good moisture condition weighs about 4,000,000 Ibs. To be 



