AVAILABILITY OF POTASH IN SOME COMMON SOIL¬ 
FORMING MINERALS—EFFECT OF LIME UPON POTASH 
ABSORPTION BY DIFFERENT CROPS 
By J. K. Plummer 
Soil Chemist, Division of Agronomy, North Carolina Agricultural Experiment Station 
INTRODUCTION 
Little direct information is obtainable regarding the relative avail¬ 
ability of potash carried in common soil-forming minerals. The data 
found are decidedly contradictory. They have either been obtained 
from the ability of weak solvents to remove potassium or have been 
adjudged from the resulting optical properties of the minerals after 
years of subjection to the forces of weathering. 
Numerous petrographic analyses of the soils of the United States 
(McCaughey and Fry , 1913 ) 1 show that only four minerals which carry 
potash are found in the very fine sand and coarse silt separates. These 
are biotite, muscovite, orthoclase, and microcline. In many of the 
residual soils, such as the Porter and Cecil series {Plummer, 1915), the 
micas are found in large quantitites, and must supply much of their 
potash. Some of the transported soils, such as those of the Atlantic 
Coastal Plain, carry comparatively little mica, but often are well supplied 
with microcline and orthoclase. 
It has been known for a good many years that certain neutral salts 
when in contact with the mineral portion of the soil cause an exchange 
of bases between the salt and soil. Owing to this action, many claims 
have been made regarding the effects of lime and other compounds for 
increasing the soluble potash of the inert soil mass. More recent experi¬ 
ments give indications that the effect of lime and gypsum in bringing 
into solution potash from the mineral portion of the soil is slight or nil. 
None of these investigations, however, as shown by the following brief 
review, have thoroughly covered the direct action of lime compounds on 
those minerals which supply the soil with potassium. 
review of previous investigations 
So far as the writer is aware, Johnstone {1889) was the first to report 
on the stability of micaceous minerals. This investigator found that, 
after suspension of mica for as much as one year in carbonated water, 
no alteration could be detected. 
Hilgard {1906, p. 51), in speaking of soils formed from mica schist, says: 
. . . mica schist, which being a mixture of quartz and mica only, not only 
weathers very slowly, but also supplies but little of any importance to plants to the 
soils formed from it. 
1 Bibliographic citations in parentheses refer to “Literature cited,” p. 314-315. 
Journal of Agricultural Research, 
Washington, D. C. 
(297) 
Vol. XIV, No. 8 
Aug. 19,1918 
Key No. N.C.-ia 
