22 
WATER REQUIREMENT OF PLANTS. 
were required to saturate 260 pounds of moisture-free soil in each 
potometer. The average moisture contents, expressed in terms of 
the dry weight of the soil, would then be as follows: 38, 31, 23, 17, 
and 13.4 per cent. The nonavailable moisture was estimated at 12 
per cent. This gave a very small margin of available moisture in 
the driest pots, and these plants often wilted and rolled. The average 
dry weight (based upon four plants) and the moisture requirement 
for the different degrees of saturation are given in Table XII: 
Table XII. — Effect of soil-moisture content on the water requirement of corn, according 
to Kiesselbach and Montgomery (1911, p. 91). 
Saturation. 
Dry weight. 
Water re- 
quirement. 
Per cent. 
Grams. 
100 
373 
290 ± 4 
80 
484 
263 ± 5 
60 
442 
239±10 
45 
297 
230± 7 
35 
112 
261 ±17 
Kiesselbach and Montgomery attribute the higher value obtained 
in " saturated" soil to some physiological disturbance, indicated by 
the reduced plant growth. The plants grown in soil 45 per cent 
and 35 per cent saturated were also much smaller than the others. 
Diminished growth is often accompanied by an increase in the water 
requirement. This is partly offset in the present case by the fact 
that the evaporation conditions to which the shorter plants were 
subjected were less severe. The relative evaporation from jars of 
water placed at 0, 2, 4, 6, 8, and 10 feet above ground in the cornfield 
was respectively 1, 1.15, 1.32, 1.53, 1.65, 1.75. 
A consideration of the probable errors indicates that an actual 
reduction of the water requirement accompanies the reduction of 
the saturation water content from 100 to 80 or 60 per cent. A 
further apparent reduction also occurs when the saturation water 
content is reduced to 45 per cent, but as already stated this may be 
due to the protection given by the taller surrounding plants. The 
probable error in the series with the lowest water content (35 per 
cent saturated) is so high as to make conclusions uncertain. 
PFEIFFER, BLANCK, AND FLUGEL's EXPERIMENTS. 
Pfeiffer, Blanck, and Flugel (1912) carried on a series of experi- 
ments with oats to determine the effect of different soil-moisture con- 
tents on the water requirement. About 18 kilograms of sand were 
used per pot. The plants were grown in three series, one kept con- 
stantly at 10 per cent soil moisture, another at 7 per cent, and a third 
allowed to fluctuate between 10 per cent and the wilting point (4 per 
cent). Twenty-four plants of Ligowo oats were used per pot. The 
pots were kept in the greenhouse during rainy weather and moved 
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