29 



acidity, when calc-nlated to the equivalent amount of calcium carbon- 

 ate, varied from 3(K> to 70<) pounds for 1 acre of soil to the depth of 1 

 foot. How far this method is applicable to Hawaiian soils is yet to 

 be determined, and efforts are being made to do this by field tests. 

 The acidity shown by this method evidently does not interfere to any 

 great extent with nitrification, for the samples examined contained 

 nitrogen as nitrates varying from 15 to 55 parts per million. In 

 determining the nitrate in these soils the method used was to add 500 

 cubic centimeters of water to 100 grams of soil, shake 8 minutes, 

 let stand 20 minutes, filter, and determine nitrates in 100 cubic cen- 

 timeters of the tiltrate by the phenol-sulphonic acid method. It was 

 found that in cases when the soil and water had been allowed to 

 stand overnight (14 hours) the nitrate had much decreased, and in 

 some cases disappeared altogether. ' This applied to all the soils exam- 

 ined, and occurred whenever the soil stood for some hours saturated 

 with water. The following example will illustrate this: 



Tarts jior 

 millidii. 



No. 1. 100 grams of soil, 500 cubic centimeters water; shaken 8 



minutes, let stand 20 minutes; nitrogen as nitrate 32. 5 



No. 2. 100 grams of soil, 500 cul)ic- centimeters water; shaken 3 



minutes, let stand 1 hour; nitrogen as nitrate 47. 5 



No. 3. 100 grams of soil, 500 cubic centimeters water, shaken 3 



minutes, let stand 22 hours; nitrogen as nitrate -l. 



No. 4. 100 grams of soil, water to saturation (75 cubic centime- 

 ters) added, let stand 22 hours; 425 cubic centimeters 

 water added, shaken 20 minutes; nitrogen as nitrate ... 4. 



With another sample of soil from the same place the time factor 

 was determined roughly by saturating 100 grams with 75 cubic centi- 

 meters water and proceeding as above in No. 4, varying the time. 

 The results were as follows: 



Parts per 

 million. 



Stood 2 hours; nitrogen as nitrate 40 



Stood 4 hours; nitrogen as nitrate - - 40 



Stood 6 hours; nitrogen as nitrate 40 



Stood 8 hours; nitrogen as nitrate 40 



Stood 10 hours; nitrogen as nitrate 40 



Stood 12 hours; nitrogen as nitrate 15 



Stood 13 hours; nitrogen as nitrate 4 



Stood 14 hours; nitrogen as nitrate 4 



Stood 15 hours; nitrogen as nitrate 4 



Soil from another place, by treatment as above, gave the following 

 figures: 



" . Parts per 



million. 



Stood 1 hour; nitrogen as nitrate 35 



Stood 12 hours; nitrogen as nitrate 30 



Stood 16 hours; nitrogen as nitrate 25 



Stood 20 hours; nitrogen as nitrate H 



Stood 24 hours; nitrogen as nitrate 11 



