EFFECT OF DRYING SOILS ON WATER-SOLUBLE CONSTITUENTS 175 



lime, magnesia, soda, oxide of iron and aluminum, phosphoric, sulfuric and carbonic acids, 

 chlorine, silica and organic matter separately. Their results vary greatly for any one con- 

 stituent because of the wide range of soils, temperatures and moisture contents used. 



These results are especially interesting since several of them were obtained by methods 

 essentially similar to those of King, who used 100 gm. of soil and 500 cc. of distilled water. 

 The soil was stirred in a mortar with enough water to make a thick paste in order to break 

 down all granules, after which the remainder of the 500 cc. of water was added. Then the 

 supernatant, turbid liquid was transferred to a pint Mason jar and, usually within 15 minutes, 

 to the Pasteur-Chamberland filter chamber. 



Filtration was accomplished by a pressure of 30 to 40 pounds. Clear extracts were ob- 

 tained in 5 to 20 minutes, depending on the type of soil, and the amount of clay and fine 

 silt remaining in suspension to coat the walls of the filters. It was during the 3 minutes 

 of active agitation that the main part of actual solution occurred. It was found that longer 

 washing did not materially increase the amount of salts going into solution. At first the 

 electrical-resistance method was employed for determining concentration but it was found 

 more accurate to evaporate definite quantides of the extract, dry in an oven and weigh. 

 NOi, HPO4, CI and SiOj were determined by methods described by Whitney and Cameron 

 (103). Comparisons were made of the salts that could be recovered from fresh soU, soil 

 quickly sun-dried and from that oven-dried at 1 10°C. Eight soils in four 1-foot sections were 

 used. In the surface foot, of four soils the oven-dry soil had more nitrates, while in the 

 other four, the fresh, moist soil had more; but in the second, third, and fourth sections the 

 nitrates were increased 108, 134 and 61 per cent, respectively. In two of the eight soils the 

 fresh sample showed considerably more HPO4 in the first section than the dry and in eight 

 instances in the other 3 feet out of the 24 possible cases the fresh soil was slightly higher. In 

 every case (except one in fourth foot), the dry soil gave up much more SO4; for the eight soils 

 the average increase for the four sections was 265, 310, 281 and 79 per cent, respectively. 

 In one instance only was the fresh soil significantly higher in HCOs while in the others the 

 dry was from 48 to 73 per cent higher. Silica was 588, 322, 237 and 236 per cent higher 

 in the oven-dried soil in the four sections. Chlorine was the only element that, on the aver- 

 age, was recovered in smaller quantity from the dry soil. The other acid radicals ran from 

 1.26 times as much nitrates up to 6.58 times as much of silica in the dry as in the fresh soiL 



Later, determinations were made of potash, lime and magnesia in the extract of fresh 

 and oven-dried soils. In part II, King reports good correlation between quantity of soluble 

 salts found, especially HPO4, and crop yields for the different soil types under investigation. 



King concluded that in oven-drying the last of the moisture, for a time at a temp>erature 

 near the boiling point, increases the solubility of salts and might be expected also to render 

 the organic matter more soluble. He also concluded that when a soil dries its salts are 

 deposited as crystals on the soil particles and salts within the granules are left on the exterior. 

 As the soil is stirred in water, these salts go into solution readily. On the other hand, in 

 a moist soil the solution is simply diluted by adding water and the dissolved salts are dis- 

 seminated through it in part by diffusion, a slow process. The solution from the dry soil is 

 removed from it before readsorption occurs. Thus, he explains the recovery of more soluble 

 material from the dry than the moist soil. 



Hilgard (30) considered the unusual productiveness of desert soils when properly watered, 

 due to an abundant supply of plant nutrients rendered available by the intense heating to 

 which these soils are subjected during the warm season. With King he believed that the 

 soluble salts, on drying, are deposited on the surface of the particles whence they may be 

 "readily abstracted by the first touch of the solvent water," and that soils retain salts in 

 a condition of purely physical adsorption. 



Stone and Monohan (98) noted that sterilizing loam increased the growth of soybeans 

 14 per cent, but that sterilizing in the same way decreased the growth of soybeans in subsoil 

 57.7 per cent. The subsoil pots showed poor, sickly development. 



