54 BULLETIN E. 



These relations of yield appear to be not only in. accord with 

 the amounts of potash found, but also in accord with what is 

 demonstrated regarding the functions of potash in plant physi- 

 ology. Loew* points out that "the paramount! importance of 

 potassium salts for every living cell is firmly established" and 

 holds that, in green plants, they are concerned not only in the 

 upbuilding of carbohydrates but in that of protein bodies as 

 well. 



Various observers have shown that when plants are placed 

 under conditions where all potash salts are excluded, not only 

 does the formation of starch stop altogether but that whatever 

 may have been present disappears and ultimately growth stops ; 

 but that, on the admission of potash salts into the plants again, 

 the formation of starch is renewed and growth carried forward. 

 With vital functions like these so intimately related to this ele- 

 ment, it is easy to understand why deficiencies of potash in 

 forms available to crops stand next, perhaps, to deficiencies in 

 nitrates in determining small yields. Indeed, it has transpired 

 in the constant cropping series begun by the writer at the Wis- 

 consin Agricultural Experiment Station in 1896, where 700- 

 pound lots of a strong virgin soil were placed under corn, oats, 

 potatoes and clover, and forced to produce two to three crops 

 annually, ihat this year (1903) when Prof. Whitson divided 

 the series into groups to test, through the application of potash, 

 nitrates, and phosphates, which ingredient most increased the 

 yield (then fallen far below the first crops), the results have 

 shown in a very striking manner that the addition of potash had 

 far greater effect than did the addition of either of the other 

 salts, and appear to indicate that these soils had either become 

 absolutely deficient in potash during the constant cropping, or 

 else that the potash still remaining was not in such form as to 

 come into solution and enter the crops with sufficient rapidity 

 to meet their needs. 



In the soil of the four plant evaporimeters t ur>on which 10 

 stalks of corni were matured on. each of four soil types, there 

 was a very appreciable decrease in the amounts of potash which 



*United States Department of Agriculture, Bureau of Plant Industry, Bul- 

 letin No. 45, page 28. 



tBureau of Soils, Relation of Differences of Yield on 8 Soil-Types to Differ- 

 ences of Climatological Environment, p. 96, F. H. King. 



