EFFECT OF SOIL FACTORS OX WATER REQUIREMENT. 
49 
WIDTSOE S EXPERIMENTS. 
Widtsoe (1909) conducted during 1904 and 1905 an experiment to 
test the effect of manure and mineral fertilizer on the water require- 
ment of corn. The amounts of mineral fertilizers used (Table 
XXXVII) were calculated upon the weight of the upper 6 inches of 
soil and were added at the beginning of each year. All the fer- 
tilizers used were incorporated with the surface soil to a depth of 6 
inches. Two open pots of College loam were used with each fer- 
tilizer treatment, one pot being planted to corn and the other kept 
barren to determine the evaporation from the soil. The pots were 
24 inches in diameter and 30 inches high. The results show a reduc- 
tion in the water requirement following the use of fertilizers, but the 
results for the two seasons are widely at variance. 
Widtsoe later used three different types of soil in investigating the 
effect of fertilizers on the water requirement of corn. The results 
are also given in Table XXXVII. One soil consisted of an unpro- 
ductive sand from a river wash, while the other two soils were pro- 
ductive. The experiments were carried on for but a single year, and 
only single pots were used for each fertilizer. The surface of the soil 
was not protected, and the evaporation was assumed to be the same 
as from bare check pots. 
The soils in the various pots used had been treated differently in 
experiments previous to 1905 as regards culture, crops grown, 
methods of irrigation, and amount of water applied, but had been 
exposed without crop to atmospheric agencies from 1905 to 1908. 
"The amount of fertilizer applied in each case was nearly five times 
larger than in 1904 and 1905. As a result the depressing effect of 
the fertilizer is observed in a number of cases." 
Table XXXYII. — Effect of fertilizers on the water requirement of corn, according to 
Widtsoe (1909, pp. 49, 52). 
Water requirement, using— 
Year and soil. 
No fer- 4 pounds °;L t 
tilizer. manure. {JJ^S 
0.01 
per cent 
NaN0 3 . 
0.1 
per cent 
KCl. 
9 
08 613 
581 
151 
257 
237 
848 
315 
431 
464 
368 
247 
640 
Water requirement, using— 
Year and soil. 
No fer- 
tilizer. 
K 
P 
N 
KN 
KP 
PN 
KNP 
1909: 
1,012 
357 
306 
686 
308 
292 
735 
391 
375 
555 
471 
385 
671 
333 
383 
178 
339 
459 
450 
280 
303 
97991°— Bui. 285—13 4 
