190 NATURE AND PROPERTIES OF SOILS 



2. Climate — Rain, humidity, sunshine, temperature, and 

 wind. 



3. Moisture and fertility. 1 



Not only do different plants 2 show a variation of transpira- 

 tion the same season, but the same plant may give a totally 

 different transpiration in separate years. This is due in part 

 to inherent differences in the plant itself. For example, the 

 extent of leaf surface or root zone would materially influence 

 the transpiration relationship under any given condition. 

 However, a great deal of the variation observed in the ratios 

 already quoted arises from differences in climatic conditions. 

 As a general thing, the greater the rainfall the higher is 

 the humidity and the lower is the relative transpiration. 

 This accounts for the high figures obtained by Widtsoe 8 in 

 Utah. Montgomery 4 found, in studying the water require- 



1 Fertility is used here in the sense of potential productivity. It 

 refers especially to the ultimately available nutrients of the soil. 



2 Miller, E. C, and Coffman, W. B., Comparative Transpiration of 

 Corn and the Sorghums; Jour. Agr. Res., Vol. XIII, No. 11, pp. 579- 

 604, June, 1918. 



8 Widtsoe, J. A., The Production of Dry Matter with Different Quan- 

 tities of Irrigation Water; Utah Agr. Exp. Sta., Bui. 116, 1912. Also, 

 Irrigation Investigations. Factors Influencing Evaporation and Trans- 

 piration; Utah Agr. Exp* Sta., Bui. 105, 1909. 



4 Montgomery, E. G., and Kiesselbach, T. A., Studies in Water Re- 

 quirements of Corn; Nebr. Agr. Exp. Sta., Bui. 128, p. 4, 1912. 



14th Ann. Rep., pp. 217-231, 1897. King used cans holding about 400 

 pounds of soil. Some were set down into the earth while others were 

 not. Part of the work was carried on in the field; the remainder was 

 run in vegetative houses. Normal soils were used. Evaporation from 

 soil was very low, water being added from beneath. The data quoted 

 are the average of a large number of tests. 



8 Leather, J. W., Water Requirements of Crops in India; Memoirs, 

 Dept. Agr., India, Chem. Series, Vol. I, No. 8, pp. 133-184, 1910, and 

 No. 10, pp. 205-281, 1911. Jars containing from 12 to 48 kilograms 

 of soil were used. Loss by evaporation was determined on bare pots. 

 The plants were grown in culture houses or in screened inclosures. 



6 Briggs, L. J., and Schantz, H. L., Relative Water Requirement of 

 Plants; Jour. Agr. Research, Vol. Ill, No. 1, pp. 1-63, 1914. Also, 

 The Water Requirements of Plants; U. S. Dept. Agr., Bur. Plant Ind., 

 Bui. 284, 1913. Plants were grown in cans holding 250 pounds of soil. 

 Evaporation from soil was prevented by means of a paraffin covering. 

 Work was conducted in screened inclosures. The data are the average 

 of several years' work. 



