JOMAL OF AGRICULTIAL RESEARCH 



DEPARTMENT OF AGRICUETURE 



Vol,. Ill Washington, D. C, October 15, 1914 No. i 



RELATIVE WATER REQUIREMENT OF PLANTS 



By Lym.\n J. Briggs, Biophysicist in Charge, Biophysical Investigations, and H. L. 

 Shantz, Plant Physiologist, Alkali and Drought Resistant Plant Investigations, 

 Bureau of Plant Industry 



INTRODUCTION 



The marked differences in the quantity of water required by different 

 species of plants for the production of a given weight of dry matter when 

 grown under the same environmental conditions is a matter of scientific 

 interest and of great economic importance in regions of limited water sup- 

 ply. The measurements which have heretofore been made have for the 

 most part been limited to a few species and have been carried out under 

 such varied environmental conditions that comparison is difficult. The 

 writers have therefore undertaken the measurement of the water require- 

 ment of representative species and varieties of the principal crop plants, 

 grown at the same place and under as nearly unif onn conditions as to time 

 as the temperature requirement and Hfe history of the different crops will 

 permit. The first series of measurements were made at Akron, Colo., in 

 191 1 (Briggs and Shantz, 1913a)'. These measurements were ex- 

 tended in 1 91 2 and 191 3 to include many species whose water requirement 

 had never before been determined. The later measurements form the 

 subject of the present paper. The writers desire to express their obliga- 

 tion to Messrs. R. D. Rands, A. McG. Peter, H. Martin, F. A. Cajori, N. 

 Peter, and G. Crawford for efficient and painstaking assistance in con- 

 nection with these experiments. 



EXPERIMENTAL CONDITIONS 



The experimental procedure in 191 2 and 191 3 was similar to that in 

 the earlier experiments. The plants were grown to maturity in large 

 galvanized-iron pots holding about 115 kg. of soil. Each pot was pro- 

 vided with a tight-fitting cover having openings for the stems of the 

 plants, the annular space between the stem of the plant and the cover be- 

 ing sealed with wax. The loss of water was thus confined almost entirely 

 to that taking place through the leaves, and the entrance of rainfall was 

 almost wholly excluded. The wax which has been found to be the most 



' Bibliographic citations in parentheses refer to " Literature cited." p. 62-63. 



Journal of Agricultural Research, Vol. Ill, No. i 



Dept. of -Agriculture, Washington, D. C. Oct. 15, 1914 



(l) G-32 



