22 
Journal of Agricultural Research 
Vol. VIII, No. i 
Such reactions as may exist can not be considered to be independent of 
the character of the potash-bearing minerals in the soil. Prianischnikow 1 
has shown with a number of different crops that marked differences 
exist in the availability of the potash in the various potash minerals, and 
that the availability corresponds approximately with the solubility of the 
potash of the different minerals in solutions of neutral salts. Of all the 
potash-bearing minerals tested, those of the feldspar group (orthoclase, 
microcline) showed the lowest available potash. 
Blanck 2 has found that the potash in biotite and muscovite, minerals 
of the mica group, is more available to plants than that in orthoclase. 
The addition of finely ground microcline and orthoclase (equivalent to 
i.6 gm. of potassium oxid) to sand (18 kgm.) having a very low potash 
content, resulted in little or no increase in the dry weight of oat plants, 
compared with plants grown in sand alone, and did not appreciably 
increase the potash content. An equal amount of potassium oxid 
applied as potassium sulphate increased the yield 70 per cent. Blanck 
concludes that the availability of the potash in potash-bearing minerals 
to plants increases proportionally to their sodium and calcium content. 3 
Many of the soils devoted to the culture of Citrus fruits in southern 
California have been derived from granite, pegmatite, or other rocks of 
this general type. Under the prevailing arid conditions the decomposi¬ 
tion of the bedrock has been slow, and small lumps of granite, feldspar, 
and silica can still be found scattered plentifully through the soil. 
Pegmatite and orthoclase were selected as types of the potash-bearing 
rocks and minerals that constitute the chief source of potassium in many 
of these Citrus soils. Samples collected near Riverside, Cal., were ground 
and passed through a 60-mesh sieve. Upon analysis by fusion, the peg¬ 
matite gave 1.50 per cent of potassium oxid and the orthoclase 12.56 
per cent. The following experiments indicate that the addition of lime 
or gypsum to soils derived from orthoclase-bearing rocks has little or no 
effect, so far as the liberation of potash is concerned. 
SOLUBILITY OF THE POTASSIUM IN PEGMATITE AS AFFECTED BY 
CALCIUM HYDRATE AND CALCIUM SULPHATE 
Ten-gm. portions of pegmatite were weighed out and placed in shaker 
bottles with 1 liter of water, together with varying amounts of calcium 
hydrate (expressed as calcium oxid), as given in Table I. These mixtures 
1 Prianischnikow, D. Vegetationsversuche mit verschiedenen kalihaltigen Mineralien. In Landw. 
Vers. Stat., Bd. 77, Heft 5/6, p. 399-411, pi. 2-6. 1912. 
2 Blanck, E. Die Bedeutung des Kalis in den Feldspaten fur die Pflanzen. In Jour. Eandw., Bd. 61, 
Heft 1, p. 1-10. 1913. 
a The solubility of the feldspar at temperatures above that of the soil is manifestly beyond the scope of 
this paper. Mention may appropriately be made, however, of a recent investigation by Stephenson, who 
has compared the action of various alkaline solutions on feldspars and hornblende at ioo° C. and above. 
(Stephenson, E. A. Studies in hydrothermal alteration. Pt. I. The action of certain alkaline solutions 
on feldspars and hornblende. In Jour. Geol., v. 24, no. 12, p. 180-199, 8 fig. 1916.) 
