EFFECT OF SOIL FACTORS ON WATER REQUIREMENT. 
15 
kilograms of soil were used. His results, which are expressed in 
terms of air-dry weight and include also the effects of fertilizers on 
the water requirement, are given in Table XXVIII (p. 38). The 
range in soil moisture in these experiments was small, and the effect 
upon the water requirement is not marked. 
WILMS S EXPERIMENTS. 
effect of different soil-moisture 
of potato tubers (green weight) 
Wilms (1899) investigated the 
contents on the water requirement 
and obtained results which are in accordance with those already noted. 
The pots contained about 17 kilograms of soil and were not covered, 
but the water was applied through a Liebscher air-circulation tube, so 
that the surface soil always remained dry. The results of the investi- 
gation, which includes also the effect of various fertilizers on the 
water requirement, are given in Table XXIX (p. 39). The mean 
values obtained by Wilms are as follows: 
Moisture-holding capacity per cent. . 33, 58, 80 
Water requirement green weight. . 39, 50, 62 
DASZEWSKl's EXPERIMENTS. 
Daszewski (1900) determined the dry weight of the tubers from a 
few of Wilms's pots. The combined data (Table V) show that the 
water requirement was greatly increased in the soil with the higher 
water content. 
Table A'. — Effect of different amounts of soil moisture on the water requirement of potato 
tubers. 1 
Water content, in terms of moisture-holding 
capacity. 
Fertilizer used. 
33 per cent. 
58 per cent. 
Mean water 
require- 
ment. 
Dry tubers. 
Water re- 
quirement. 
Dry tubers. 
Water re- 
quirement. 
Grams. 
50.7 
58.8 
61.2 
90.9 
55.7 
98 
84 
85 
87 
92 
Grams. 
72.5 
68.8 
98.1 
147.0 
78.7 
156 
161 
131 
136 
150 
127 
Na 2 S0 4 
122 
K 2 SO« 
108 
KN0 3 
111 
MgS0 4 
121 
89 
147 
1 Combined from Wibns (1899, p. 288-2S9) and Daszewski (1900, p. 240); the data as given are the mean of 
two pots. 
fortier's experiments. 
Fortier (1903), using pots 18 inches in diameter, 30 inches dee]), and 
containing 19 plants of Swedish Select oats, obtained the results given 
in Table VI. The first column of the table gives the total amount of 
water added to each pot expressed in terms of inches of rainfall. The 
water lost apparently includes the evaporation from the soil, though 
285 
