15 



samples taken on 11-12-14 and 11-20-14 gave higher values for the sap 

 from plants overfed with potassium sulfate than those treated with am- 

 monium sulfate, but later in the year in the set of 12-9- 14 (Samples i 

 and 2) the relative values are reversed. 



In the set of 1 2-9-14 plants treated with potassium sulfate at the rate 

 of 1000 g. per section per application were still apparently normal, al- 

 though the osmotic pressure amounted to 15.25 atmospheres, while plants 

 treated with one-half this weight of ammonium sulfate possessed an os- 

 motic pressure of only 14.16 atmospheres and showed signs of injury. 

 Injury, on the other hand, had not appeared on plants treated with am- 

 monium sulfate (250 g. per section per application) when the osmotic 

 pressure amounted to 12.42 atmospheres as compared to 1 1 . 34 atmos- 

 pheres in the adjacent "check" section (12-9-14 — 10 a.m.). 



The higher value of Sample i over Sample 2 (of the set of 12-9- 14 — 

 10 A.M.) was correlated with a greater degree of injury by the ammonium 

 sulfate. Injury appeared on the plants from sections to which potassium 

 sulfate was applied, only when an osmotic pressure of over twenty atmos- 

 pheres was reached (1-9-15), and an osmotic pressure value up to 15.50 

 atmospheres was found in plants on soil treated with sodium phosphate, 

 without injury being apparent. The determination of the value on the 

 sap from plants treated with acid phosphate gave 1 6 . 1 1 atmospheres, 

 yet these plants exceeded in size and vigor those to which no fertilizer 

 was applied ('1-9-15). The conclusion to be drawn from these facts 

 is that, with a single fertilizer, injury from overfeeding becomes apparent 

 when a certain osmotic pressure is reached, but that this value is different 

 for different fertilizers. 



The injury from applications of sodium chloride at the rate of 125 g. 

 per section per application, occurred at approximately the same time, 

 was very similar to, and was of about the same degree as that from ap- 

 plications of potassium sulfate, in four times these quantities. The rela- 

 tive osmotic pressure values are given in Samples 9 and 10 (1-9-15). 

 The solubilities of these salts, as pointed out on page 2785, at 0° are 

 35.7 and 8.5, respectively, giving a ratio roughly of 4 to i. 



Effects of Overfeeding on the Total Acidity of the Cell Sap. — Reaction 

 tests with litmus paper showed that the soil receiving no fertilizer or 

 only manure was neutral or slightly alkaline in the fall, and that a gradual 

 change to slight acidity took place during the winter. Commercial 

 acid phosphate, dried blood and ammonium sulfate upon the soil each 

 increased the total acidity,* the first one immediately after application, 



* It is not likely that the hydrogen-ion concentration of the soil solution was greatly 

 increased by addition of commercial acid phosphate, since the formula used in its prep- 

 aration prevents the presence of free sulfuric acid by providing a slight excess of tri- 

 calcium phosphate. Salm,''^ using a hydrogen electrode apparatus, found [H] = 3.3 X 

 io~' for the di-hydrogen sodium phosphate at 18° in o.i N sol. 



