70 
WATER REQUIREMENT OF PLANTS. 
EFFECT OF THE AMOUNT OF GROWTH OR NUMBER OF PLANTS PER 
UNIT OF SOIL MASS ON THE WATER REQUIREMENT. 1 
VON SEELHORST AND BUNGER's EXPERIMENTS. 
Von Seelhorst and Biinger (1907) measured the water requirement 
of summer wheat when five plants were grown in each pot and when 
single plants were used. The experiments were carried out in pots 
containing 12 kilograms of soil. The results are given in Table 
XXXII (p. 44) . In 14 out of 15 trials a higher water requirement was 
obtained when five plants were grown in a pot than when single plants 
were used. The increase in the water requirement was, however, 
small, averaging about 15 per cent for the low water-content series, 
and about 4 per cent for the high water-content series. It will be 
noted that the amount of dry matter produced varied greatly ac- 
cording to the treatment, and that in every case a single plant pro- 
duced more than one-half as much dry matter as five plants taken 
together. As already suggested (p. 44), this indicates a deficiency 
of plant food in the small pots containing the five plants. 
EFFECT OF THE AGE OF THE PLANT ON THE WATER REQUIREMENT. 
VON SEELHORST'S EXPERIMENTS. 
Von Seelhorst (1908a) experimented with lupine to determine the 
effect of duration of growth on the water requirement. The experi- 
ments were started on August 2, and the plants in eight pots were 
i Von Seelhorst (1910a, p. 91) in presenting the data used in compiling Table XLV (p. 56) arranged the pots 
without respect to previous treatment or previous crop, in the order of decreasing yields, as follows: 
Dry matter. 
Water requirement, 
including evaporation. 
Actual. 
Mean. 
Actual. 
Mean. 
Grams. 
526.0 
482.3 
482.1 
458. 5 
414.8 
399.4 
397.4 
395.5 
393.5 
390.6 
390.0 
350.5 
339.0 
Grams. 
Grams. 
389 
685 
666 
720 
731 
777 
761 
768 
754 
763 
793 
840 
900 
Grams. 
1 394. 4 
1 769 
From these results he concludes that the water requirement increases as the production of dry matter 
decreases. The amount of growth was, however, greatly influenced by the fact that some pots contained 
more plant food than others, due to differences in the previous treatment. The unfertilized pot produced 
a light crop, and, as already shown in the section dealing with the effect of fertilizers on the water require- 
ment, a deficiency in the plant-food supply greatly increases the water requirement. 
It does not necessarily follow from this experiment, therefore, that the water requirement is inversely 
proportional to the amount of growth. These data are of value rather in showing the effect of fertilizer 
and of the previous crop upon the water requirement, and have been thus considered by the writers. 
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