12 USE OF FELDSPATHIC EOCKS AS FEETILIZEES. 



take a long time to grow, and this present inquiry is mainly conjfined 

 to availability in a single year from finely ground material. 



In order to put the availability of the potash in very finely ground 

 feldspathic rocks to actual test the writer undertook some prelimi- 

 nary experiments in the greenhouse. Tobacco was selected for the 

 experiments because, besides being extremely dependent upon an 

 abundant potash supply, this plant is particularly well adapted to 

 observation and control. Artificial soils were made up of clear, 

 close-grained white sand and finely gi'ound feldspar, running about 

 8 per cent potash, such as is ordinarily prepared for use in the pot- 

 teries, and which will pass through a standard sieve of about 200 

 meshes to the linear inch, having apertures approximately 0.0024 

 inch square. Tobacco seedlings were set out in this mixture and 

 carefully fed from day to day with dilute solutions of ammonium 

 nitrate and ammonium phosphate in order to supply the necessary 

 amount of nitrogen and phosphoric acid. In addition to this, a 

 small amount of salts, containing lime, magnesia, and iron, was also 

 added to the food solutions. Every care was taken, however, to see 

 that no potash, except that wdiich might be supplied by the feldspar, 

 obtained access to the plants. 



For the sake of comparison, plants were also grown at the same 

 time in a rich composted loam soil, which contained an abundance of 

 all plant foods, including potash. Although the artificial sand-feld- 

 spar soil was hard and apparently unsuited to the groAvth of plants, 

 the tobacco nevertheless throve well in it, and showed at no time 

 the slightest indication of potash starvation. When the experiments 

 were finally abandoned, the tobacco plants growing in the sand 

 feldspar had attained a height of about 3 feet, and showed every 

 indication of being as perfectly nourished as those growing in the 



rich soil. 



In addition to the above experiments, seedlings were also set out 

 in a poor, unfertilized soil, with and without the addition and ad- 

 mixture of a certain proportion of the ground feldspar. Here also 

 the availablity of the feldspar potash was clearly indicated. 



These experiments, which were made in the summer of 1905, were 

 not considered conclusive, but were sufficiently encouraging to justify 

 further and more systematic investigation. Before proceeding it 

 was of course necessary to look up the literature of the subject, in 

 order to see to what extent ground feldspar had been experimented 

 Avith by other investigators. A bulletin of the United States De- 

 partment of Agriculture, which appeared a short time after the con- 

 clusion of the preliminary experiments described above, contains a 

 partial reference list of previous publications along this line." 



o Bui. 30, Bureau of Soils, U. S. Dept. Agriculture, p. 26. 

 104 



