EFFECT OF DRYING SOILS ON WATER-SOLUBLE CONSTITUENTS 185 



Method of collecting soil 



The surface vegetation was removed and the surface of the soil leveled. Steel tubes of 

 2 J inches inside diameter at the cutting edge and 2| inches above it were used. A block of 

 wood was placed on the tube which was then driven into the soil with a sledge hammer to a 

 depth of 8 inches. The soil within the tube constituted the "tube" surface sample. Heavy 

 paper held in place by rubber bands was immediately placed over each end of the tube to 

 reduce evaporation and aeration. 



A sample was then collected from immediately around the tube with a Ij-inch auger to 

 the same depth. This was immediately placed in a 2-quart Mason jar with a minimum of 

 evaporation and aeration. This was the "auger" surface sample. 



The hole was enlarged and dug out with a spade to a depth of 12 inches and the soil from 8 

 to 12 inches discarded. The tube was driven down from 12 to 20 inches and protected as 

 before. This stratum 12 to 20 inches constitutes the "tube" subsurface sample. The 

 "auger" sample was collected and sealed as before. All samples were taken to the laboratory. 

 The paper cap at the top of the steel tubes was removed and melted paraffin poured on so as 

 to seal it. When the paraffin had solidified, the tubes were inverted, a portion of the soil 

 removed and tlie tube sealed as above. Both tubes and jars were properly labeled and placed 

 in a refrigerator, at a temperature of 8 to 12°C. in order to keep the soil as nearly in its 

 original condition as possible by minimizing biological activity. 



All soil samples were collected and treated in this way. 



General procedure 



Duplicate 100-gm. samples were weighed into aluminum dishes of known weight and placed 

 in an electric oven at a temperature of about 105°C. for 8 hours to determine the total mois- 

 ture. After these had been weighed, water-free soil from another dish was added to each 

 to make exactly 100 gm. of water-free soil for the determination of total soluble salts and 

 nitrates. 



Lyon and Bizzell (63) have shown that aerating after heating has a marked influence on 

 the disappearance of total soluble solids. For that reason, all soils both before and after 

 heating were kept in closed containers to reduce aeration to a minimum. 



The percentage of moisture in the fresh soil was calculated on the basis of water-free soil 

 as 100 per cent. The method of obtaining a quantity of moist soil precisely equivalent, to 

 100 gm. of water-free soil, was to add to 100 gm. of moist soil 1 gm. of moist soil for every 

 per centum of moisture in it. King's (45) method was followed throughout. Five hundred 

 CO. of distilled water was used with 100 gm. of water-free soil. The soil was placed in a mortar, 

 sufficient water added to make a thin paste, rubbed with a pestle for 3 minutes, and the 

 mixture transferred to a porcelain pitcher, stirred a moment, and allowed to stand 20 minutes. 

 Soil and water were then transferred to a Pasteur-Chamberland filter and a pressure of 15 to 

 20 pounds applied. 



In the case of moist soil containing, for example, 20 per cent water, 480 cc. of water was 

 added, making a total of 500 cc. precisely the same as in case of the dry soil. In this way, 

 the calculation is simplified and the comparison is more accurate than where 100 gm. of both 

 moist and water-free soil are used and 500 cc. of water added to each. For example, if 100 

 gm. soil contains 20 per cent water, only 80 gm. of soil are washed, 500 cc. -f- 20 gm., or cc, 

 of water from the soil, a total of 520 cc. The ratio of soil to water is 1 : 6.5, instead of 1 : 5, as 

 with 100 gm. of dry soil to 500 cc. of water, for which our plan calls. 



The first 50 cc. of the soil extract was discarded. Two 125-cc. portions from each of the 

 duplicate soil samples, or four portions from each soil, were placed in silica dishes and 

 reduced to dryness on a water-bath, dried in the electric oven at 105''C., cooled in a 

 desiccator, and weighed on an analytical balance. This weight of solids represents one- 

 fourth of what was actually dissolved in the extract from the original 100 gm. of soil. 



