EFFECT OF VARIATION IN MOISTURE CONTENT ON 

 THE WATER-EXTRACTABLE MATTER OF SOILS 



By J. C. Martin and A. W. Christie, Division of Agricultural Chemistry, California 

 Agricultural Experiment Station 



The question of the possible effect produced on the water-soluble 

 matter by variations in the moisture content of the soil became of interest 

 in connection with investigations of the water extracts of soils carried on 

 at this laboratory.* In the work referred to, the soils were maintained at 

 all times as near their optimum moisture contents as was practicable 

 with the large quantities (i,8oo pounds) of soil involved. Some variation 

 was, however, found to take place between waterings and is deemed to 

 be inevitable in experiments of that type. The purpose of the present 

 study was to determine to what extent variations in moisture content of 

 soils mpdify the magnitudes of their water extracts and thus vitiate con- 

 clusions drawn from our own and similar experiments. 



DESCRIPTION OF SOILS 



The two soils studied herein are regarded as typical of the two classes 

 used in much of the recent work of this laboratory. No. i is a Yolo silty 

 clay loan and is the same soil as that called "No. i " in the investigations 

 of Stewart.* No. 2 is a sandy loam very similar to the "No. 11" soil 

 described in the same publication. The portions of the soils used in this 

 investigation were taken from bins in which they have been stored for 

 several years and hence show a relatively great accumulation of water- 

 soluble matter. They were practically in the air-dry condition, No. i 

 containing 5 per cent moisture and No. 2 about 2.5 per cent. The 

 optimum water content for the silty clay loam soil is 22 per cent, while 

 that of the sandy loam is 15 per cent. 



PROCEDURE 



Four 500-gm. portions of soil No. i were placed in quart Mason jars 

 and brought to a moisture content of lo, 15, 20, and 25 per cent, respec- 

 tively, making 16 jars or samples in all. The same procedure was fol- 

 lowed for soil No. 2, except that the moisture contents were 5, 10, 15, 

 and 20 per cent. These moisture contents were chosen as those covering 

 the range of possible moisture variations of these soils in the field during 

 the season. The lowest moisture content maintained is approximately 

 the air-dry condition, while the highest is slightly above optimum for 

 each soil. 



1 Stewart, Guy R. effect of season and crop growth in modif^tng the sou, extract. In 

 Tour. Agr. Research, v. 12, no. 6, p. 311-368, 24 fig., pi. 14. 1918. Literature cited, p. 364-368. 



Journal of Agricultural Research, Vol. XVIII. No. 3 



Washington, D. C. Nov. i. 1919 



sp Key No. Calif. -23 



(139) 



