1922] WOODARD—SOIL FERTILITY 85 
solubility of potassium in California soils when gypsum was added, 
and the solubility of potassium decreased as the amount of gypsum 
used was increased. BREZEALE and Briccs (5) grew wheat in 
water cultures, using extracts from orthoclase minerals with and 
without gypsum. The gypsum did not increase the availability 
of the potassium to the wheat. Morse and Curry (52) treated 
feldspars with gypsum for ten weeks in water, filtered off the solu- 
tion and analyzed for potassium. Only slightly more potassium was 
found than when no gypsum was used. McMItrar (49) treated 
five different soils with gypsum for three months and analyzed for 
soluble potassium. Gypsum was used at the rate of ten tons per 
acre and resulted in an increase in soluble potassium in every case. 
TRESSLER (69) found an increase in soluble potassium in some soils, 
but no increase in others when treated with gypsum. Lipman 
and GERICKE (39) obtained an increase of available potassium in 
greenhouse soil, a slight increase in adobe soil, and no increase in 
sand. FRaps (22) grew plants in pots of soil treated with gypsum 
and analyzed the plants for potassium. He found no increase in 
potassium in plants grown on the gypsum-treated soil above that 
on the soil without gypsum. He reports no analyses of the soils 
used, however, so it is not known whether these soils were deficient 
in potassium or not. If the soil has sufficient potassium in an 
available form to supply all the plants’ needs, there would not 
likely be any increased absorption even if the soil treatment dis- 
solved some of the insoluble potassium compounds in the soil. 
On the other hand, in a soil deficient in potassium and sulphur, 
the application of gypsum or any other fertilizer containing sulphur 
would stimulate the growth of roots, and the increased size of the 
toot system would make it possible for the plant to absorb more 
potassium. This increased absorption would take place regardless 
of any possible effects on the solubility of the potassium compounds 
in the soil. 
The experiments of McMitiar (49), Suances (69), and 
LipMaNn (39) indicate a greater solubility of potassium in some 
soils when treated with gypsum, but other soils show no effect, 
while Briccs and BreEzEALE (6) report a decrease in solubility 
when gypsum was used. It seems, therefore, that the beneficial 
