448 ALFALFA FARMING IN AMERICA. 



It has often been noted that as a rule isolated alfalfa plants 

 set seed far more profusely than those in all but the thinnest 

 stands. Observations, on this point have been made in various 

 parts of the Great Plains and intermountain areas and in the 

 farther Southwest. On the Arlington Experimental Farm, near 

 Washington, D. C, an experiment was performed to determine 

 the effect of different degrees of isolation on the seed-setting 

 ability of alfalfa. In this experiment, cuttings from a heavy- 

 seeding plant were rooted in . the greenhouse and later set out 

 at varying intervals. Inasmuch as these plants were propagated 

 vegetatively from the same mother plant, they did not show the 

 Individual variation mentioned above that would have entered into 

 the experiment had seedling plants been utilized. 



The plants occupying a space equivalent to a 7-inch square pro- 

 duced a maximum of 38 pods, while those having at their com- 

 mand a space equal to an 11-inch square produced a maximum of 

 96 pods. The highest number of pods formed on plants grown in 

 rows 39 inches apart and 18 inches apart in the rows was 505. 



It will be noted that the yields were in almost direct proportion 

 to the areas occupied. However, it was evident that the plants 

 having the greatest distance between them had not utilized fully 

 their allotted space. This was accounted for by the fact that it 

 was their first season's growth. An adjoining two-year-old cutting 

 from another plant of similar seed-producing tendencies produced 

 2,080 pods, and this without utilizing all of the space of 18 inches 

 in the 39-inch row assigned to it. Although part of this difference 

 may have been due to inherent capacity, the chief explanation for 

 it must be sought in the firm establishment of the plant and its 

 greater maturity. 



Just why the isolation of plants increases the production of seed 

 has not been fully determined, but it is apparent that one of the 

 factors involved is the increased amount of sunlight available to 

 the plant. It has often been observed that trees grown on the 

 banks of irrigation ditches in alfalfa fields or along the margins 

 of fields always interfere with normal seed production as far as 

 the infiuence of their shade extends. In the course of an experi- 

 ment on the seed setting of alfalfa it was found that partial shad- 

 ing materially reduced the quantity of seed produced by plants 

 not already receiving more than the optimum amount of sunlight. 



When alfalfa plants have sufficient space for full development 

 they have approximately equal illumination on all sides. With 

 the plants so far apart that when fully developed they barely 

 occupy the ground the potential seed-producing surface exposed 

 on an acre is nearly double that of a thick stand. In the latter. 



