28 
Journal of Agricultural Research 
Vol. VIII, No. i 
SUMMARY 
It is stated in agricultural treatises that the application of lime to a 
soil liberates potash from the soil minerals. This subject is of special 
import to the Citrus industry of southern California in which commer¬ 
cial fertilizers are extensively used and heavy applications of lime and 
gypsum are sometimes made. 
Samples of pegmatite and orthoclase were collected near Riverside, 
Cal., representing, respectively, types of the potash-bearing rock and 
mineral from which many of the Citrus soils appear to be derived. These 
samples were finely ground and shaken for a number of days with aqueous 
solutions of calcium hydroxid and of calcium sulphate in graduated con¬ 
centrations. The calcium-hydrate solutions did not modify the solu¬ 
bility of the potassium in either pegmatite or orthoclase. Gypsum solu¬ 
tions depressed the solubility of the potassium in orthoclase, the quantity 
of potash in solution decreasing progressively as the concentration of 
the calcium sulphate increased. 
Similar tests were made upon a virgin soil of a granitic type from the 
experiment station near Riverside, Cal. The solubility of the potash 
was not measurably different in distilled water and in solutions of calcium 
hydrate or calcium sulphate. 
The addition of calcium sulphate to a Citrus soil which had been under 
cultivation for some time and which was more granular and less weath¬ 
ered than the virgin soil, decreased the solubility of the potash. 
The potassium content of wheat seedlings was practically the same 
when grown (i) in water containing finely ground orthoclase and (2) in 
a saturated calcium-sulphate solution containing the same quantity of 
orthoclase. 
Similar experiments in which a Citrus soil was used instead of ortho¬ 
clase showed a decreased absorption of potassium by wheat seedlings in 
the presence of calcium sulphate. 
In brief, the experiments indicate that the availability to plants of the 
potash in soils derived from orthoclase-bearing rocks is not increased by 
the addition of lime or gypsum. In some instances a marked depression 
of the 'solubility of the potash in the presence of gypsum was observed. 
These conclusions are based both on the results of the analyses of the 
solutions and on the measurement of the potash content of wheat seed¬ 
lings grown in the solutions. 
