The Possible Effect of Hydrogen-ion Concen- Tration on the Absorption of Potassium and Phosphorus by Wheat Plants under Field Conditions'

While studying the factors affecting the absorption of mineral elements by plants, the writer showed that the hydrogen-ion concentration of the medium affects the absorption of potassium and phosphorus by wheat seedlings grown in water cultures. (4) ^ More phosphorus was absorbed from potassium phosphate solutions with initial pH values of 5.0 and below than from those with pH values of 6.0 and 7.0. The results for potassium were not so definite as those for phosphorus. In several cases the absorption of potassium by the wheat seedUngs was higher from tjie nearly neutral than from the acid solutions (pH 5.0 and below); in other cases the results were not consistent. The concentrations of potassium phosphate used in these experiments were, for reasons explained in the article referred to, relatively high, but in concentrations as low as 14 parts per million of potassium and 12 parts of phosphorus (50 parts per million of mönopotassium phosphate) the general character of the results was the same. From solutions of the lower concentrations (beginning with 500 parts per million of monopotassium phosphate), the absorption of potassium by the seedhngs was practically always higher when the initial hydrogen-ion concentration of the solutions had a pH value of 7.0 than when it was 4.9. In view of the fact that potassium phosphate salts are all soluble it has been concluded that this effect of hydrogen-ion concentration on the absorption of phosphorus and potassium is physiological in nature.