AVAILABILITY OF POTASH IN CERTAIN ORTHOCLASE- 
BEARING SOILS AS AFFECTED BY LIME OR GYPSUM 
By Lyman J. Briggs, Biophysicist in Charge , and J. F. BrEazeale, Laboratory 
Assistant , Biophysical Investigations , Bureau of Plant Industry, United States Depart¬ 
ment of Agriculture 
INTRODUCTION 
Most soils appear to contain sufficient calcium to supply an abundance 
of that element so far as the actual food requirements of the crop are 
concerned. In the majority of cases in agricultural practice the appli¬ 
cation of lime, either as quicklime (CaO) or as the carbonate (CaC 0 3 ), is 
made either on account of its effect upon the physical condition of the 
soil or to neutralize soil acids. There are cases, however, where a rela¬ 
tively small application of lime will accomplish beneficial effects that are 
not readily explainable on the basis of either of these postulates. The 
same is true with calcium sulphate, or gypsum (CaS0 4 .2H 2 0). 
Such instances have perhaps helped to formulate the idea, apparently 
quite widely held, that calcium replaces potassium in the potash-bearing 
minerals of the soil, liberating this plant-food element. Thus, Hilgard, 1 
in summarizing the important chemical effects of calcium carbonate, 
includes among others “the rendering available, directly or indirectly, 
of relatively small percentages of plant food, notably phosphoric acid 
and potash”; and again, in speaking of calcium sulphate, Hilgard makes 
the following statement: 
Being soluble in 400 parts of water, it easily penetrates downward in most soils, and 
in doing so effects changes in the zeolitic portions, setting free potash from silicates 
and thus indirectly supplying plants with this essential ingredient in a soluble form. 
About 200 pounds per acre is an ordinary dose. 2 
Lyon, Fippin, and Buckman speak of the action of gypsum in lib¬ 
erating potassium, as “a property with which it has generally been 
credited” . . . “the actual extent of which has never been very 
clearly demonstrated.” 3 
Andre 4 reports a greatly increased solubility of the potash in micro- 
cline in the presence of calcium carbonate or calcium sulphate, the 
solubility being 2 and 2.5 times, respectively, that in water alone. 
1 Hilgard, E. W. Soils . . . p. 379* New York, 1906. 
3 Hilgard, E. W. Op. dt„ p. 43. 
3 Eyon, T. E., Eippin, E. O., and Buckman, H. O. Soils, their Properties and Management, p.. 543. 
New York, 1915. 
4 Andr£, G. Deplacement de la potasse contenue dans certaines roches feldspathiques par quelques 
substances employees comme engrais. In Compt. Rend. Acad. Sci. [Paris], 1 .157, no. 19, P- 856-858. 1913. 
Journal of Agricultural Research, Vol. VIII, No. 1 
Washington, D. C. Jan. 2,1917 
gp Key No. G—102 
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