30 
WATER REQUIREMENT OF PLANTS. 
requirement, and further experiments are desirable, using a larger 
number of pots to reduce the experimental error. 
Table XIX. — Effect of cultivation on the water requirement of corn, according to Widt- 
soe (1909, p. 19). 
Soil. 
Satura- 
tion. 
Treatment. 
Water require- 
ment. 
Ratio, cultivated to 
uncultivated. 
1902 1903 ! 1904 1902 ' 1903 1904 Mean 
Sand 
College loam. 
Sanpete clay 
Clay 
Per cent. 
15 
20 
25 
30 
/Cultivated . . . 
\Uncultivated 
/Cultivated . . . 
(Uncultivated 
(Cultivated . . . 
(Uncultivated 
(Cultivated . . . 
(Uncultivated 
732 
4.14 
295 
523 
2SU 
439 
582 
753 
236 
378 
388 
225 
908 
615 
595 
1.61 
. 56 0. 62 
.64 .68 
.78 i 
1.61 
0.25 .48±.09 
1.03 .78±.10 
I 
.78 
CONCLUSIONS. 
The results of Sleskin and of Widtsoe lead to opposite conclusions 
regarding the effect of cultivation on the water requirement. Neither 
experiment is free from certain assumptions relative to the amount 
of evaporation from the soil, and consequently neither experiment 
can be considered as showing conclusively that cultivation has a 
direct effect on the water requirement independent of soil evaporation. 
EFFECT OF THE SOIL MASS OX THE WATER REQUIREMENT. 
hellriegel's experiments. 
Hellriegel (1883) measured the water requirement of red clover 
using culture jars of different sizes. The results are given in 
Table XLIX (p. 59). The differences shown in his experiments are 
without significance, owing to the high probable errors. A similar 
series dealing with barley is given in Table LII (p. 62). No con- 
sistent difference in the water requirement was found attributable 
to the amount of soil used. 
leather's experiments. 
Leather (1910) used in his fertilizer experiments jars ranging in 
capacity from 15 to 31 kilograms of soil. He states that this varia- 
tion in the mass of soil used may affect the transpiration ratio 10 to 
20 per cent, the smaller jars giving the higher water requirement. 
His results are given in Table XXXIX (p. 51) hi connection with 
his fertilizer experiments. The writers have combined these results 
in Table XX, calculated with respect to the size of the jar used. 1 
The mean values show with one exception that the use of the smaller 
jar gives a higher water requirement. 
i The average result for each set of jars of a given size includes several fertilizer treatments. The kind 
of treatment and the number of jars used with each treatment are, however, uniform for a given crop and 
year for each size of jar, so that the results for the same crop and year are comparable. 
285 
