10 USE OF FELDSPATHIC EOCKS AS FERTILIZERS. 



and it must therefore be almost entirely free from mica or iron-bearing 

 minerals. For this reason there are large quantities of materials at 

 every feldspar quarry which, though unfit for pottery use, would be 

 valuable if any method were known of making potash available. 



The question whether fine-ground feldspar can be used as a potash 

 fertilizer has been a matter of controversy for many j^ears. There is 

 a large and widely scattered literature on the subject, an examination 

 of which shows that the matter has been debated with much vigor 

 and sometimes with prejudice and intolerance on both sides. It is 

 easy to find the published records of a number of experiments, made 

 by trained and thoroughly competent agriculturists, which tend to 

 show that ground feldspar is an efficient potash fertilizer. On the 

 other hand, a number of experiments seem to indicate that the potash 

 is onl}^ slightly available, while others would appear to show that the 

 ground rock is entirely useless. On account of the large interests 

 involved in the settlement of this question it is not difficult to see 

 why vigorous differences of opinion, and even unjust prejudice, 

 should have arisen. When, however, trained investigators reach 

 opposite conclusions, based upon experimental evidence, we are forced 

 to the opinion that while ground feldspar may be a useful fertilizer 

 under certain conditions it is not so under others. 



It is the object of this bulletin to present and discuss as fully as 

 possible all the evidence that can be obtained on both sides of this 

 important question. The great demand for information on the sub- 

 ject which has arisen and the numerous misstatements that have been 

 printed make it desirable to present the evidence obtained up to date, 

 even though many more years Avill be necessary for the conclusion of 

 careful systematic investigation under crop and field conditions. 



The availability' of potash contained in feldspathic rock must 

 depend upon several important considerations, which can best be 

 expressed by a discussion of the following questions : 



(1) Is the potash locked up in feldspar and the feldspathic rocks, such as 

 granite, gneiss, rhyolite, syenite, etc.. to any extent available as a fertilizer 

 when these rocks are crushed or ground to fine powder? 



(2) If the first question can be answered in the affirmative, what influence 

 does fineness of grinding have on the question, and to what degree of fineness is 

 it necessary to grind in order to make a sufficient amount of potash available 

 in the first season after application? 



(3) What would be the cost of using ground rock in place of the soluble com- 

 pounds which up to the present time have been exclusively used, and would 

 there be economy in so doing? 



(4) Could any subsequent damage result from the use of ground rock ; and if 

 so, how would such damage compare with that which follows the continued use 

 of soluble compounds, such as chlorids, sulphates, and carbonates? 



(5) If it should l)e determined that the potash in ground feldspathic rock is 

 only partially available as a fertilizer, is there any method or process by which 

 the ground rock could be treated so as to increase this availability? 



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