BULLETIN OF THE 



"ffiOFAfflU 



No. 228 



Contribution from the Bureau of Plant Industry, Wm. A. Taylor, Chief 

 May 22, 1915. 



(PROFESSIONAL PAPER.) 



EFFECT OF FREQUENT CUTTING ON THE WATER REQUIRE- 

 MENT OF ALFALFA AND ITS BEARING ON PASTURAGE. 1 



By Lyman J. Briggs, Biophysicist in Charge of Biophysical Investigations, and H. L. 

 Shantz, Physiologist, Office of Alkali and Drought Resistant Plant Investigations. 



INTRODUCTION. 



The determination of a plant's efficiency in the use of water at 

 different stages in its development is a problem of much interest, 

 but one which involves serious experimental difficulties on account 

 of the constantly changing environmental conditions and the con- 

 sequent necessity of extensive multiplication of the series of experi- 

 mental plants. The present experiments (Table I) were designed to 

 determine (1) whether alfalfa in the early stages of growth following 

 a cutting has a water requirement differing from the water require- 

 ment of the plant during the normal period of growth, and (2) to 

 what extent frequent cutting or grazing during the hottest part of 

 the year modifies the seasonal water requirement. 



METHOD. 



Two standard sets of selected Grimm alfalfa, 2 each consisting of 

 six pots of plants, were employed in these experiments. The plants 

 were treated in the usual way 3 up to the time of the first cutting, on 

 July 26, at which time care was taken to leave the basal shoots, so 

 as to insure the uninterrupted growth of the plants. Following this 

 date, the growth on the pots of series B was cut back weekly in a 

 manner somewhat resembling pasturage (fig. 1), all of the material 

 thus removed from each pot being preserved separately. The growth 

 of the plants in series A was allowed to proceed without interruption 



1 The experiments reported in this bulletin were conducted at Akron, Colo., in 1912. The methods 

 employed were essentially the same as those described in Bulletin 284 of the Bureau of Plant Industry, 

 entitled "The Water Requirement of Plants. I. — Investigations in the Great Plains in 1910 and 1911." 

 Sealed pots were used to prevent evaporation from the soil and the entrance of rainfall. The writers are 

 indebted to A. M. Peter, R. D. Rands, H. Martin, and G. Crawford for assistance given at Akron in 1912. 



2 The strains were selected by A. C. Dillman, of the Office of Alkali and Drought Resistant Plant Inves- 

 tigations. 



3 See Bulletin 284 of the Bureau of Plant Industry, previously mentioned, for details of these experi- 

 ments. Series B was, however, started 10 days later than the check series (A), owing to the necessity of 

 replanting. 



88195°— Bull. 228—15 



