Nov. 1. 1919 Variation in Moisture Content of Soils 143 



tent variation was between 22 per cent and 16 per cent, with an average 

 of 19 per cent; for soil No. 2, the extremes of moisture variation were 

 16 per cent and 11 per cent, with an average of 13 percent. These are 

 variations of approximately 5 per cent from the optimum moisture 

 contents and show the tendency of the soil to be slightly below the 

 optimum in moisture. In the present study the only significant varia- 

 tions from the maximum quantity of extractable material are observed 

 when the soils are either approaching the air-dry condition or are in a 

 moisture-saturated condition. Looking again at the results recorded 

 in the table and calling especial attention to those of soil No. i at 20 per 

 cent moisture, at 15 per cent, and even at 25 per cent, and also to those 

 of soil No. 2 at 15 per cent and at 10 per cent — these being variations of 

 from 5 to 7 per cent below their optimum moisture contents — it is readily 

 seen that at any one sampling date the quantities of water-extr actable 

 materials are exceedingly uniform and represent no significant differences. 

 Therefore it is concluded that in water-extraction studies of soils the 

 moisture content at which the soils are maintained need not necessarily 

 be limited to a narrow range. 



SUMMARY 



(i) The water-soluble constituents of two soils of very different type 

 have been studied at four moisture contents. 



(2) The moisture contents approaching the air-dry condition show a 

 decided tendency to depress the nitrates and potassium in both soils 

 and the sulphates in the silty clay loam only. These depressions are 

 reflected in the total dissolved material. 



(3) The excess water in the sandy loam soil causes a disappearance 

 of nitrates and also decidedly depresses the potassium, calcium, and 

 magnesium, these losses also being reflected in the total solids extracted. 



(4) Considerable variations in moisture contents of soils, provided 

 the saturation point is not reached, do not appreciably modify the 

 results obtained by the water-extraction method. 



134793°— 19 3 



