sept. 9,1918 Variations in Moisture Content of a Loess Soil 
479 
to the development of both the driest and the moistest conditions or¬ 
dinarily encountered there, and the degree of moistness is expressed as 
the ratio of the water content of the soil to the hygroscopic coefficient. 
The soils were loessial silt loams in adjacent fields, including a clean 
summer fallow, a cornfield, grass fields, and an area of subsoil exposed 
by grading operations and kept free of vegetation. 
The extremes were shown by the fallow and the grass fields. As the 
frost disappeared from the ground at the close of a fortnight of rainless 
weather the ratios in both were found as high as at any time later in the 
season, except immediately after very heavy rains, being alike in the two 
fields and averaging 3.1 to 3.2. A few hours after the cessation of a rain 
of 2.8 inches, ratios of 3.7 to 3.9 were found in the surface 6-inch section 
in both fields, but of only 2.9 to 3.3 in the second 6-inch section. 
The lowest ratios in the portions of the foot section below the immediate 
surface were found in the grass fields, where, during dry periods, they fell 
as low as 1.2, the twelfth inch becoming as dry, and this as quickly, as 
the overlying levels, evidence that the chief loss of water ws*s through 
transpiration. In the cornfield as the plants approached maturity the 
moisture was withdrawn uniformly from the different levels but the 
ratios did not fall below 1.5. 
In the fallow the soil at only a few inches from the surface remained 
moist throughout the driest periods. In the second 6-inch section the 
ratio did not fall below 2.6, varying during the season only between the 
limits 2.6 and 3.1. Even in the fourth inch the ratio did not fall below 
1.8, while in the second it was below 2.0 for only very short periods. 
In the grass fields after the ratios had been reduced to a low point only 
rains amounting to 2.0 inches or more were able to penetrate to a depth 
of 12 inches, the water from lighter rains being held within the surface 
foot until it was transpired by the plants or evaporated from the surface. 
In the fallow with its moist soil the penetration w r as not much greater, 
but this is to be attributed to the rain falling more rapidly than it could 
be absorbed or retained on the plant free surface. 
In the grass fields, and in the cornfield after the plants were well grown, 
the moisture was lost chiefly through transpiration, while on the fallow 
and exposed subsoil it was lost through evaporation and run-off, but 
little of the rainfall of the five months covered by the study reaching the 
second foot. In the grass field doubtless practically all the 13.8 inches 
that fell were so returned to the atmosphere, while in the fallow probably 
less than the equivalent of 2.0 inches of rain was accumulated in surface 
soil and subsoil together. 
The exposed subsoil kept free of vegetation differed markedly from the 
fallow with ordinary surface soil, the maximum ratio being only 2.4 to 
2.5 and in the second 6-yich section the ratio during the season varied 
only between 2.0 and 2.3. The differences in the maximum ratio between 
the first and the second 6-inch sections in the fields with ordinary surface 
