20 Journal of Agricultural Research voi.xii, no. i 



The method has been used for indicating the reaction of the soil film 

 water. The effects of several fertilizer materials have been studied on 

 the H-ion concentration of various field soils, receiving applications of 

 such fertilizers for a number of years. Lastly, the effect of ammonium 

 sulphate and monocalcium phosphate on the reaction of soil film water 

 have been investigated. 



METHODS OF INVESTIGATION 



The apparatus for measuring the H-ion • concentration of soil suspen- 

 sions and extracts was essentially that described by Hildebrand {8), and 

 modified by Sharp and Hoagland. Palladium was substituted for plati- 

 num as the electrode, which was treated in a manner similar to that 

 described by Findlay (6) for coating electrodes. The supply of hydrogen 

 was obtained by electrolyzing water, with potassium hydro xid as the 

 electrolyte. All the precautions of rigidity of connections, insulation of 

 apparatus, time (which often varied) for estabhshment of equihbrium 

 between soil and solution, coating electrodes, and prevention of loss of 

 CO2 were strictly observed. 



It might be said in passing that no difficulties were encountered due 

 to the reduction of nitrates to ammonia, as has been suggested. 



In the preparation of soil suspensions, unless otherwise stated, the 

 arbitrary ratio of 10 gm. of air-dried soil to 100 c. c. of as pure distilled 

 water as obtainable was used. In the case of field soils their content was 

 determined as soon after sampling as practicable, and the same ratio of 

 soil to water maintained. All samples except those taken directly from 

 the field were screened through a 2-mm. sieve. 



In all cases the readings became constant in a few minutes. Dupli- 

 cate readings on the same sample of soil could easily be read to 0.02 volt. 

 However, to be certain 'that equilibrium had been established the elec- 

 trode was allowed to remain in contact with solution for 30 minutes. 

 It was almost impossible to get such closely agreeing results as 0.02 

 volt with different samples of the same soil. This can be accounted 

 for in the lack of uniformity of mixing. 



The results are reported in the usual manner for such measurements, 

 units of gram-molecules of H ion per liter. The tables of Schmidt {11) 

 were used in securing the H-ion concentration from the voltmeter read- 

 ings. 



RESULTS OBTAINED 



In Table I will be found the results of measurements of the H-ion 

 concentrations of 68 samples of untreated soils, including subsoils, which 

 represent a wide range in types of five series. Included in this table 

 are results derived from five samples of treated soil. The samples are 

 taken as a fair representation of the soils common to the area of the 

 southeastern portion of the United States, which extends from and 

 including the Appalachian Mountains to the Atlantic Ocean. 



