42 
WATER REQUIREMENT OF PLANTS. 
Iii general the experiments show a consistent and decided decrease in 
the water requirement of potatoes when moderate amounts of potash 
are added, the water requirement decreasing gradually with the increase 
in potash until about 0.06 per cent has been added. The addition of 
potash in excess of this amount increases the water requirement. 
The effect of different amounts of potash on the water requirement 
of tobacco is also shown in Table XXX. Here, as in the experiments 
with potatoes, the water requirement gradually decreases with the 
gradual increase of potash. The lowest water requirement occurs 
with about 0.04 per cent of potash. 
The results with white mustard show a decrease in water require- 
ment with an increase in potash. Similar results are shown for buck- 
wheat, for Magdeburg chicory, and for oats (Table XXX). 
The results of Wilfarth and Wimmer' s experiments are consistent 
and show practically without exception a gradual decrease in the 
water requirement when potash is added in small amounts. If too 
much potash is added (more than 0.04 to 0.06 per cent) the water 
requirement is again slightly increased. 
The effects of different amounts of nitrogen and sodium on the water 
requirement of potatoes, tobacco, buckwheat, mustard, chicory, and 
oats are shown in Table XXXI. As a rule, the addition of nitrogen 
lowers the water requirement of each crop considered. The excep- 
tions show a difference so small as to be well within the limit of 
probable error. Except in the case of buckwheat, oats, and chicory, 
the addition of sodium did not consistently lower the water require- 
ment. In some cases it seemed to increase the water requirement, as 
in the experiments with potatoes when potash was also added. 
Table XXXI. — Effect of different amounts of nitrogen and sodium on the water require- 
ment of crops, 1 according to Wilfarth and Wimmer. 
Crop and period. 
Soil per pot. 
Fertilizer per pot. 
Mean 
dry 
matter. 
Mean 
water 
K 2 
Na 2 
N 
require- 
ment. 
Potatoes: 
May 5 to Sept. 13, 
1899. 
Sand, 6,670 grams; turf, 455 
grams; water, 1,800 grams; 
water increased Aug. 24 
to 2,010 grams. 
Sand, 6,670 grams; turf, 455 
grams; water, 1,780 grams; 
water increased July 5 to 
2,255 grams, and July 18 
to 2,375 grams. 
Grams. 
Grams. 
Grams. 
0.560 
1.120 
1.120 
2.800 
1.120 
2.100 
2.100 
2.800 
1.820 
2.800 
2.800 
1.750 
1.750 
2.240 
2.240 
Grams. 
27.0 
33.8 
33.7 
50.3 
50.5 
68.7 
69.5 
82.8 
108.3 
121.5 
105.3 
48.6 
47.3 
97.5 
96.4 
1,720 
1,345 ±55 
1,310±137 
502 ±76 
0.620 
0.282 
.282 
.282 
.282 
.846 
.846 
.846 
878 ±72 
648 ±15 
.620 
662 ±2 
283±4 
407±11 
2G7±10 
Apr. 25 to Sept. 15, 
1900 
1.240 
453 ±6 
508 ±25 
3.100 
495 ±1 
.846 
. 846 
332 ±6 
3. 100 
336 ±23 
' Computed from data of Wilfarth and "Wimmer (1902), as follows: Potatoes, pp. 10-15; tobacco, pp. 
44-51; buckwheat, pp. 54-55; mustard, pp. 64-65; chicory, pp. 74-75; oats, pp. 82-83. Determinations were 
in duplicate except where no probable error is given, in which case only one determination was made. 
285 
