CLIMATE AND PLANT GROWTH. 



9 



being 19.3 per cent in the fertile loam soil and 15.6 per cent in the 

 infertile loam. 



After sifting and preparing the soils for the reception of the plants 

 according to the procedure previously described, two hermetically 

 sealed batteries of each soil type were planted with sprouts of wheat 

 of about equal leaf area and thrift, two with Canadian field peas, and 

 one each with mountain brome grass. Thus 10 plants each of wheat 

 and peas, and 5 of brome grass were grown in each soil type. The 

 potometers were placed in the meteorological station of the aspen-fir 

 type, where the plants were grown until inclement weather set in in 

 the autumn. 



The water requirements for the production of a unit of dry matter 

 of field peas, mountain brome grass, wheat, and wheat heads in the 

 two soils are shown in Table 1, and graphically in figure 2. 



Table 1. 



-Water requirement in grams of peas, brome grass, icheat, and loheat 

 heads per gram of dry matter. 



Sofl. 



Peas. 



Brome 

 grass. 



Wheat. 



Wheat 

 heads. 



Tnfprtllfi soil 



841 

 467 

 80.3 



1,339 

 1,110 

 20.6 



472 

 343 

 37.6 



1,370 



Fertile soil 



407 





236.6 







In all cases notably more water was required for the production of 

 a unit of dry matter in the infertile loam soil than in the fertile loam. 

 The difference was greater in the peas than in the brome grass or the 

 wheat. The brome grass was less influenced than either wheat or 

 peas. The greatest difference occurred in the production of wheat 

 heads, there being a requirement of 237 per cent more in the infertile 

 than in the fertile soil. Under natural conditions brome grass grows 

 in soils of relatively low fertility, and the species succeeds in com- 

 pleting its life cycle in soils similar to the infertile soil here experi- 

 mented with. 



In summing up the total water used by the plants grown in the tAvo 

 selected soils it was found that a great deal more was consumed by 

 the plants grown in the fertile than in the infertile soil, despite the 

 fact that much more water was required by the plants grown in the 

 infertile soil per unit of dry matter. 



It is noteworthy that a wide variation exists between the water 

 requirement per unit of dry matter of brome grass and that of peas 

 and wheat, even when the plants are grown in the smne sort of soil. 

 Thus in the case of the fertile soil brome grass uses more than twice 

 as much water as the other two species, while in the infertile soil the 

 ratio is practically the same.^ This wide difference in water require- 



^ For a review of literature bearing on the subject, see Briggs, L. J., and SLantz, H. L. 

 The Water Requirements of Plants, II. A Review of the Literature. U. S. Dept. of 

 Agr. B. P. I. Bull. 285. 1913. 



