Aug. 19,1918 Availability of Potash in Soil-Forming Minerals 
301 
The results obtained from these experiments indicate only small 
differences in the solubility of potash in distilled water. Biotite and 
muscovite appear to give up somewhat more of this plant nutrient to 
water than do the feldspars. These differences are small, however, and 
may be due to experimental error. 
With carbonic acid as the solvent the divergence in the amounts of 
potash going into solution is more marked. More than four times as 
much potash of biotite is dissolved as is carried by microcline. Musco¬ 
vite stands next to biotote in the solubility of its potash, and orthoclase 
is slightly ahead of microcline. 
These findings agree rather closely with the vegetative experiments 
detailed later and follow the same order as those of Fraps ( 1912 ), in 
which a weak solution of nitric acid was used as the solvent. 
Calcium bicarbonate has not shown any power to unlock potash from 
any of the minerals. With biotite and microcline there are slight losses 
of potash when this material is used in connection with water charged 
with carbon dioxid. Only very small gains from the use of the bicar¬ 
bonate are discernible with muscovite and orthoclase, gains so small as 
to be considered negligible and to have no practical significance. 
Briggs and Breazeale (1917) have recently reached the same conclusions 
from the use of calcium hydroxid and gypsum on orthoclase and certain 
orthoclase-bearing soils. 
vegetative experiments with the common soil-forming minerals 
The solubility investigations just given have shown rather marked 
differences in the power with which potash is held in the two micas and 
feldspars. For the purpose of supplementing the laboratory data, pot 
experiments were begun in which four different crops were grown out 
of doors to maturity. These were oats (Avena saliva ), soybeans (Sofa 
max), rye (Secale cereale) t and cowpeas (Vigna sinensis ). 
Description op Pot Experiments 
soil used 
The soil used in this investigation was taken from the no-treatment 
plots of the Edgecombe (N. C.) Branch Station, where experiments to 
determine its fertilizer requirements have been running for the past 15 
years. The field tests (Kilgore et al. y 1914) indicate rather conclusive^ 
that potash is one of the limiting elements of this soil; also that the 
available plant nutrients have been reduced to a minimum on the plots 
receiving no additions. The soil was taken from the plots to a depth 
of 6 % inches. Tables III and IV give the chemical and mineralogical 
composition of the soil used. 
64613°—18 - 2 
