54 Journal of Agricultural Research voi. m. No. i 



COMPARISON OF THE WATER REQUIREMENT OF CROPS AT AKRON, 

 COLO., IN 1911, 1912, AND 1913 



Climatic conditions at Akron during the summer of 1912 were less 

 severe than during the preceding summer. The rainfall in 1 91 2 was much 

 greater than in 1 91 1 , the temperature was lower, and the evaporation was 

 less. These conditions were apparently due in part to a marked reduc- 

 tion in the intensity of the solar radiation at the earth's surface following 

 the eruption of Mount Katmai, Alaska, early in June, 191 2, the dust 

 from which produced a haze in the upper atmosphere. Abbot and Fowle 

 (1913) observed a maximum reduction in the solar radiation of about 20 

 percent at Bassour, Algeria, and at Mount Wilson, Cal., Kimball (1913a, b) 

 reports an average reduction of 17 per cent in the intensit}' of the solar 

 radiation at Mount Weather, Va., during the last half of 1912, while Briggs 

 and Belz (1913) have shown that there was a general reduction in the 

 evaporation from a free-water surface during the summer months follow- 

 ing the eruption. It is consequently of interest to determine whether the 

 diminution in the intensity of the solar radiation was accompanied by a 

 reduction in the water requirement in 191 2. Such a comparison is possi- 

 ble in connection with the Akron experiments, since a large number of the 

 varieties employed in the experiments of 191 1 were also included in the 

 1 91 2 measurements. All varieties showed in 191 2 a marked reduction 

 in the water requirement as compared with 191 1. The measurements 

 for each year are given in Table XXXII, together with the ratio of the 

 1912 to the 191 1 measurements. The 1912 measurements show an aver- 

 age reduction in the water requirement of 21 ±2 per cent for the 25 varie- 

 ties tested during both years. The individual ratios fluctuate somewhat, 

 doubtless owing in part to errors of experiments,' but in part also to the 

 different response of individual varieties to changed climatic conditions. 



1 It should be mentioned here that the plants were fertilized in 1912 and not in 1911. This is a matter of 

 importance in this connection, because it is well established that any deficiency in plant food increases 

 the water requirement. The effect of the addition of fertilizer on the water requirement was measured 

 both years. The use of fertilizer resulted in a slight reduction (6±2.3 per cent) in the water requirement 

 of Kubanka wheat at Akron in 1911, comparing pots 7 to 12, fertilized, with pots 1 to 6. unfertilized. These 

 pots stood side by side in the inclosure. (6Ve Briggs and Shantz, 1913a, p. 19.) In 1912 the fertilized 

 Kubanka wheat plants showed a slight increase in water requirement — namely, 5 ±2.3 per cent, compar- 

 ing pots I to 6 against pots 7 to 12. The differences in each instance are without significance when the 

 errors are considered and are furthermore of opposite sign, so that the addition of fertilizer may be con- 

 sidered to have had no effect on the water requirement, so far as Kubanka wheat was concerned. Rich 

 surface soil from the same source was employed in the experiments of both years. 



