24 
WATER REQUIREMENT OF PLANTS. 
the amount of soil evaporation from the series, factors which obvi- 
ously have no dependence one upon the other; and, second, that 
if the soil evaporation from the two series was made equal, the water 
requirement of the two series would have to be equal, irrespective of 
the method of treatment! It is evident from this analysis that the 
method of reduction employed by Pfeiffer, Blanck, and Fliigel is not 
sound, and that consequently no weight can be attached to the data 
as given. The data without the correction for evaporation are, 
unfortunately, not given in the original paper. 
Table XIII. — Effect of different soil-moisture contents on the water requirement of 
oats, 1 according to Pfeiffer. Blanck, and Fliigel {1912, p. 230). 
Nitrogen 
applied 
per pot. 2 
Water requirement with — 
High water 
content, 
10 per cent. 
Low water 
content, 
7 per cent. 
Varying 
water con- 
tent, 4 to 10 
per cent. 
High water 
content 
and shade, 
10 per cent. 
Mean . 
Grams. 
0.355 
.710 
1.065 
1.420 
1.775 
2.130 
Mean 
397 ±5 
388 ±4 
372 ±3 
373 ±6 
397 ±4 
414 ±7 
348 ±5 
341±2 
304 ±7 
371 ±3 
386 ±5 
372 ±4 
344±1 
281 ±4 
273 ±3 
292 ±4 
307 ±4 
301 ±4 
406 ±2 
419±2 
392 ±4 
401 ±4 
433 ±4 
383±4 
374 
357 
336 
359 
381 
368 
390 ±2 
354±2 
300±2 
410±2 3 
363 
i Twenty-four plants of Ligowo oats were grown in each pot. The pots contained 18 kilograms of sand 
of low moisture-holding capacity. There were four pots for each determination. The dry matter pro- 
duced is not given. 
2 Applied as ammonium nitrate. 
3 Pfeiffer, Blanck, and Fliigel omitted four pots in calculating this mean because the plants were not 
artificially shaded. These pots apparently formed the series whose mean is 383±4. 
CONCLUSIONS. 
In general, the results of the experiments herein recorded show an 
increase in the water requirement when the water content of the 
soil approaches either extreme. Many of the experiments were con- 
ducted in open pots and the evaporation estimated by means of 
check pots, which is an uncertain procedure. Extreme moisture 
conditions might, however, affect the water requirement indirectly. 
With a high water content, the aeration would be reduced and the 
soil solution would be diluted. In the case of soils kept at a low 
water content, the small amount of water required from time to 
time to bring the pot to normal weight is sufficient to moisten only 
a comparatively small portion of the soil mass. In effect, then, the 
low soil-moisture plants are growing in a very restricted soil mass as 
compared with plants grown with an optimum soil-moisture content. 
This condition might cause an increase in the water requirement of 
plants grown in a comparatively dry soil due to a deficiency of plant 
food. In view of these considerations the writers believe that the 
direct influence of soil-moisture content on the water requirement 
can not be established without further investigation. 
285 
