140 Journal of Agricultural Research voi. xviii, no. 3 



The jars were then buried in the ground to the level of the soil inside. 

 The covers were set on loosely to allow free circulation of air and at the 

 same time prevent excessive evaporation. The area occupied was shaded 

 to prevent heating the jars and metallic covers by the sun's rays. At 

 frequent intervals — two weeks or oftener, depending on the weather — 

 enough distilled water was added to bring the soil in each jar to its correct 

 moisture content. Since this is a study of the effect of moisture content, 

 it was necessary to keep that factor constant. 



Two days after the soils were first moistened, one jar of each soil at 

 each of the various moisture contents was removed and mixed. A 

 50-gm. portion was dried to constant weight to check the moisture per- 

 centage. Soil equivalent to 340 gm. in the water-free state was extracted 

 with 1,700 cc. of distilled water, inclusive of the water in the soil, thus 

 insuring a i to 5 extraction, which was made after the manner described 

 by Stewart.^ The remainder of the soil was used to determine the con- 

 centration of the soil solution, by the freezing-point lowering, as described 

 by Bouyoucos and McCool.^ This procedure was repeated three times 

 during the period of the experiment at varying intervals of time; the 

 total length of time between the first and last sets of analyses was 22 

 weeks, which is longer than a normal growing season. 



Table I gives a complete resume of the results obtained. The con- 

 centration of the soil solution is reported in atmospheres of osmotic 

 pressure, the analyses of the water extracts as parts per million of the 

 water-free soil. 



DISCUSSION OF RESULTS 



Knowledge of the inherent variations in the methods used is very 

 essential in a study of this nature. For a detailed description of the 

 methods employed reference is made to two recent publications from 

 this laboratory.^ It is desirable to draw conclusions as to differences 

 only where such variations are of considerable magnitude, 20 per cent 

 or more. It is also evident that comparisons should be made only 

 between results obtained at the same sampling date, since it is known 

 that there are seasonal fluctuations due to other factors. 



Osmotic pressure; of the soiIv soi^ution and totaIv solids. — These 

 two determinations are placed together for consideration because of the fact 

 that they are known to be directly related, as has been shown by Hoagland.* 

 The most striking feature shown is the decrease of soluble matter in soil 



' Stewart, Guy R. op. cit. 



2 Bouyoucos, G. J., and McCooL, M. M. The freezing-point method as a new means of measur- 

 ing THE concentration OF THE SOIL SOLUTION DIRECTLY IN THE SOIL. Mich. AgT. Exp. Sta. Tech. Bui. 

 24, p. 592-631, 2 fig. 1916. 



' Stewart, Guy R. op. cir. 



Christie, A. W., and Martin, J. C. the volumetric determination of sulfates in water ex- 

 tracts of soils. 7rt Soil Science, V. 4, no. 6, p. 477-479. 1917. 



* Hoagland, D. R. The freezing-point method as an index of variations in the son, solution 

 DUE to season and crop growth. In Jour. Agr. Research, v. 12, no. 6, p. 369-395, 8 fig. 1918. Literature 

 cited, p. 394-395- 



