18 



USE OF FELDSPATHIC ROCKS AS FERTILIZERS. 



(440 to 660 pounds) as ground feldspar added to the hectare (2.47 

 acres). The results of weighings of crop yield, made on the basis 

 of 100 plants from each trial, are given in the following table : 



Weight of crop of oats from, seven i}lats of 100 plants each, grown tvith various 



fertilizers. 



Kind of fertilizer. 



Unfertilized 



Phosphate and potassium sulphate 



Phosphate and 300 feldspar potash 



Phosphate and Chile saltpeter 



Phosphate, Chile saltpeter, and potassium sul- 

 phate 



Phosphate, Chile saltpeter, and 200 feldspar potash. 

 Phosphate, Chile saltpeter, and 300 feldspar potash . 



Equivalent 

 yield of 



grain per 

 hectare. 



Kilograms. 



216 



6,400 



6,450 



7,150 



9,470 

 7,000 

 7,240 



Nilson's results are most unfavorable to ground feldspar, as an 

 inspection of the figures shows, but as a very good yield was obtained 

 by the use of Chile saltpeter and phosphate without any additional 

 potash, the experiments are not very conclusive. Chile saltpeter is 

 a crude nitrate of soda which sometimes contains potash salts. It is 

 possible that in all these experiments there was a tendency to over- 

 feeding rather than to underfeeding. 



In 1890 Sestini « published the results of a very interesting inves- 

 tigation of the decomposing action of plant roots on feldspar. A 

 coarse feldspathic granite sand from the island of Elba was first 

 carefully washed to remove all adherent earth or plant food, and 

 then mixed with certain amounts of carbonate, phosphate, and sul- 

 phate of lime. The nitrogen was supplied in the form of ammonium 

 nitrate. Various plants and grasses were grown in this mixture 

 under very careful test conditions. The crops matured well, and 

 at the end of about a year it was shown that a very considerable 

 decomposition of the feldspar had taken place. Sestini concluded 

 that the decomposition of the feldspar went on much more rapidly 

 under the influence of plant growth than had previously been 

 supposed. 



In 1901 Headden,'' working at the Colorado experiment station, also 

 independently, carried on some interesting experiments on the availa- 

 bility of potash contained in ground feldspar. To quote this author's 

 own words: 



We endeavored to determine whether the feldspar could furnish potash to 

 plants. For this purpose the perfectly fresh mineral was used, pulverized 

 as already described in imitation of the soil, i. e., the particles varied from 



a Landw. Vers. Stat., 1900, 54, 147. 

 i-Bul. 65, Colorado Exp. Sta., p. 30. 



104 



