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 Briggs (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. McMillar (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 

 root 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 McMillar (49), Tressler (69), and 

 LiPMAN (39) indicate a greater solubiHty of potassium in some 

 soils when treated with gypsum, but other soils show no effect, 

 while Briggs and Brezeale (6) report a decrease in solubility 

 when gypsum was used. It seems, therefore, that the beneficial 



