466 INVESTIGATION BY CULTURE EXPERIMENTS 



measured by the nitrogen or organic carbon, while it is extremely 

 rich in potassium. 1 



The total supply of phosphorus in the plowed soil (6| inches 

 deep) is less than would be required for 35 crops of corn yielding 

 100 bushels of grain and 3 tons of stover, while the total nitrogen 

 content even to a depth of 40 inches is less than would be required 

 for 60 such crops, or for less than 90 if only the grain were removed, 

 although the total potassium to a depth of 40 inches is sufficient 

 to meet the requirements of zoo-bushel crops of corn every year 

 for more than 4 thousand years, or for more than 16 thousand 

 years if only the grain is removed. Notwithstanding these positive 

 facts, based upon absolute chemical analysis, showing such an 

 enormous supply of potassium and a relatively small supply of 

 nitrogen, the addition of soluble potassium salts, while not yielding 

 profitable results, has actually produced a larger average increase 

 than has been produced by nitrogen applied in dried blood on the 

 Antioch soil experiment field about five miles from the Wisconsin 

 line, in Lake County, Illinois, on the late Wisconsin yellow-gray 

 silt loam, thus affording a good illustration of the fact that systems 

 of soil treatment for permanent agriculture should not be based 

 solely upon previous culture experiments. 



This soil is deficient in active humus, and the soluble potassium 



1 It is appropriate to mention in this connection that Doctor A. S. Cushman 

 of the United States Department of Agriculture has recently emphasized (Science 

 (1905), 22, 838; and U. S. Dept. of Agr. Bureau of Plant Industry Bulletin 104) 

 the possibility of using powdered granite and felspar as a source of potassium 

 for fertilizing purposes, although some previous experiments with felspar (Svenska 

 Mosskulturfar. Tidskr. (1903), 77, 360; (1904), 18, 33, 73) have not given en- 

 couraging results. While it is by no means certain that granite averaging 4 per 

 cent of potassium or felspar with 8 or 10 percent of potassium may not be used with 

 profit under some conditions, as where it can be secured as waste or by-product at 

 very low cost near lands actually deficient in potassium, it is worth while to know 

 that at $3 per ton for powdered granite the surface 20 inches of the principal 

 types of soil in the late Wisconsin glaciation already contains about $6000 worth 

 of potassium per acre in the form of finely powdered granitic rock. In other 

 words, two tons of this soil (or three tons of any silt loam soil in the Illinois corn belt) 

 spread over an acre of land would supply as much potassium, and in the same form, 

 as would be supplied by a ton of average powdered granite. 



While the phosphorus content of the surface soil of most $150 Illinois land can 

 be doubled by investing $25 to $40 per acre in raw rock phosphate at $7.50 per ton, 

 to double the potassium content by applying powdered granite at a cost of only 

 $3 a ton would cost from $1200 to $1800 per acre. 



