Nov. II, i9i8 Soil Acidity as Affected by Moisture Conditions 329 



(11) In correlating the soluble iron and aluminium with the acidity 

 obtained from the potassium-nitrate extracts, it was apparent that the 

 titrated acidity could not be entirely explained on this basis. Doubtless 

 this acidity is partly due to soluble acid organic compounds. 



(12) The measurable acidity of acid soils varies to a large degree 

 under different conditions of moisture and aeration. These variations 

 are due to chemical rather than physical changes in the soils. 



(13) The extreme sensitiveness of the chemical compounds of soils 

 and the wide variations caused by changing moisture conditions leads 

 to the conclusion that some soil investigations should be conducted 

 with undried samples. 



(14) The soil moisture of acid soils is acid in reaction as shown by 

 hydrogen-ion determinations. As the cell sap is also acid it is not 

 necessary to consider that calcium is first changed into the form of 

 bicarbonate before it can aid in nitrification or be assimilated by plants. 



(15) A condition of acidity is produced in humid soils due to the leach- 

 ing of the strong basic elements in the drainage water, by the removal 

 of bases in crops, by the decay of carbonaceous and nitrogenous sub- 

 stances, and by the hydrolysis of mineral compounds and organic matter. 



LITERATURE CITED 

 (i) Conner, S. D. 



1916. ACID SOILS AND EFFECT OF ACID PHOSPHATE AND OTHER FERTILIZERS 



UPON THEM. In Joiir. Indus, and Engin. Chem., v. 8, no. i, p. 35-40, 

 2 fig. 



(2) 



1917. THE EFFECT OF DRAINAGE ON SOIL ACIDITY. In Science, n. s. v. 46, 



no. I 188, p. 346. 



(3) Gillespie, L. J. 



I916. THE REACTION OF SOIL AND MEASUREMENTS OF HYDROGEN-ION CONCEN- 

 TRATION. In Jour. Wash. Acad. Sci., v. 6, no. i, p. 7-16, 2 fig. 



(4) Jones, C. H. 



i915. method for determining the lime requirement of soils. in 

 Jour. Assoc. Off. Agr. Chem., v. i, no. i, 43-44. 



(5) NoYES, H. A., and Yoder, Lester. 



1918. CARBONIC ACID GAS IN RELATION TO SOIL ACIDITY CHANGES. In Soil. 



Sci., V. 5, no. 2, p. 151-161, 4 fig., pi. I. 



(6) Sharp, L. T., and Hoagland, D. R. 



I916. acidity and ADSORPTION IN SOILS AS MEASURED BY THE HYDROGEN 



ELECTRODE. In Jour. Agr. Research, v. 7, no. 3, p. 123-145, i fig. 

 Literature cited, p. 143-145. 



(7) Truog, Emil. 



I918. SOIL acidity: I. ITS RELATION TO THE GROWTH OF PLANTS. In Soil 



Sci., V. 5, no. 3, p. 169-195. References, p. 193-195. 



