EFFECT OF SOIL FACTORS OX WATER REQUIREMENT. 
13 
Table II shows that the production of dry matter was very much 
reduced by the low soil-moisture content. The water requirement 
also decreased gradually but consistently with the decrease in the 
water content of the soil, except for grain production in the case of 
the lowest moisture content, which was apparently too low to sup- 
port good growth, as is shown by the small amount of dry matter 
produced. 
hellriegel's experiments. 
Hellriegel (1883) gives the results of three years' observations on 
the effect of soil-moisture content on the water requirement of bar- 
lev. The pots used in his investigation contained about 4 kilograms 
of soil. Surface evaporation in the experiments conducted in 1871 
was reduced by the use of covers cemented to the pots. The size of 
the opening for the plants is not stated. In his earlier experiments 
a correction for the direct evaporation was made, based upon the 
loss from the check pots. Hellriegers results are given in Table III. 
Table III. — Effect of different soil-moisture contents on the voter requirement of barley, 
according to Hellriegel (1883). 
Water content, in terms of moisture-holding capacity. 
Vear and production. 1 
5 per 
cent. 
10 per 
cent. 
20 per 
cent. 
30 per 
cent. 
40 per 
cent. 
60 per 
cent. 
80 per 
cent. 
1869. 
r. u /Mean weight... grams.. 
17.9 
254±10 
14.6 
168 
23.9 
258±2 
21.8 
216 
25.4 
281 ±13 
22.8 
240 
24.5 
Dry matter. . . .{ Water re( f lliren f ent . . . . 
298±4 
1870. 
Drv matter /height grams. . 
i>r\ matter. . . -^ Vater requ irement . . . . 
0.1 
940 
3 
180 
19.8 
223 
19.7 
277 
Year and production. 
1871. 
Drv matter J height grams. 
L r> matter. . . .^ Vater requirement 
Water content, in terms of moisture-holding 
capacity. 
5 to 15 
per cent. 
192 
15 to 25 
per cent. 
31.3 
239 
20 to 60 
per cent. 
49.0 
261 
40 to 80 
per cent. 
38.9 
287 
1 Three pots used in each determination in 1869; single pots in 1870 and 1871. 
These results indicate also that the water requirement of plants 
decreases within limits as the soil-moisture content is lowered, but 
is also accompanied by a decrease in dry matter. In the duplicated 
series of experiments the reduction of the moisture content from 
80 per cent saturation to 20 per cent reduced the water requirement 
of barley about 15 per cent. 
MAERCKER S EXPERIMENTS. 
Maercker (1896) investigated the influence of soil-moisture con- 
tent on the water requirement of white mustard in connection with 
285 
