Vol. VIII. No. 199. 



THE AGRICULTURAL NEWS. 



389 



ALFALFA GROWING FOR SEED 



PRODUCTION. 



Circular No. 24 of the Bureau of Plant Industry of 

 the United States Department of Agriculture deals 

 with the raising of alfalfa in cultivated rows for seed 

 production in semi-arid regions. As part of the informa- 

 tion is interesting in connexion with West Indian 

 conditions, it is given here : — 



In Bulletin 118 of this Bureau, attention was directed 

 to the fact that cultivated alfafa is not a homogeneous 

 species, but is composed of numerous races, strains, varieties, 

 and even sub-species. These vary greatly in many charac- 

 ters, and especially in their seed-producing capacity, no pure 

 varieties of known high value comparable with those we have 

 of corn, wheat and other crops having as yet been establish- 

 ed. It has also been noted that the individuals constituting 

 these diverse races, elementary .species, or whatever they may 

 be called, exhibit great variation among themselves. It has 

 often been observed that, as a rule, isolated alfalfa plants set 

 seed far more profusely than those in all but the thinnest 

 stands. 



Why the isolation of plants inci'eases the production of 

 seed has not been fully determined, but it is apparent that 

 one of the factors involved is the increased amount of sun- 

 light available to the plant. It has often been observed that 

 trees grown on the banks of irrigation ditches in alfalfa fields, 

 or along the margin of fields, always interfere with normal 

 seed production as far as the influence of their shade extends. 

 In the course of an experiment on the seed setting of alfalfa, 

 it was found that partial .shading materially reduced the 

 quantity of seed produced by plants not already receiving 

 more than the optinmm amount af sunlight. When alfalfa 

 plants have sufiieient space for full development, they have 

 approximately equal ilhmiination on all sides. 



In addition to the injurious influence of shade, the crowd- 

 ing of plants interferes with seed production by depriving 

 them of sufficient moisture to enable them to mature 

 their seed properly. This, of course, is true only in areas 

 where the rainfall is light. On the other hand, in sections 

 where irrigation is practised, thick stands, by checking 

 evaporation, bring about such moist surroundings in fields as 

 to promote unfavourable conditions, and so to [irevent 

 maximum yields of seed. 



The lower shoots, which usually appear when the plant 

 begins to bloom, are developed at the expen.se of the seed 

 crop. The energy that should be devoted solely to the 

 maturing of the seed is diverted by this new growth. Per- 

 haps the most important factor influencing the development 

 of these lower .shoots, which are to form the succeeding crop, 

 is the water content of the soil. It the moisture supply be 

 ample, the lower shoots commence their growth about the 

 time the plant comes into bloon;. This is disastrous to the 

 seed-crop, and for this reason it is necessary that there be 

 a sufficient shortage of moisture at this time to retard, or 

 prevent altogether, the development of these shoots. In the 

 seed-producing sections of the more humid parts of the Great 

 Plains area, profitable crops of alfalfa seed are usually obtained 

 only in the occasional seasons of drought which is so extreme 

 that the yield of other crops is greatly reduced. 



Drought is used here in a qualified sense. There must, 

 of course, be enough moisture in the soil to enable the .seed 

 to mature fully; otherwise it will be deficient in germinating 

 power. On the other hand, the soil must not contain enough 

 moisture to force into growth the crown buds that produce 

 the succeeding crop. 



Insect visits are essential to the proper pollination of 

 the alfalfa flower. If fertile seed is to be produced in any 

 quantity, it is necessary that a certain explosive mechanism 

 within the flower be released. By the explosion of an alfalfa 

 flower is meant the snapping out of the stamens and pistil 

 from the wings and keel, which had hitherto enveloped them, 

 to a new position against the standard. This takes place 

 when certain insect visitors insert their nectar-gathering 

 organs into the flower. The impact of the stigma and 

 stamens against the body of the inspect appears to have at 

 least three immediate and important results : (1) the 

 wounding of the stigmatic surface of . the pistil, making it 

 more susceptible to fertilization; (2) the contact of the 

 sensitive surface with pollen borne on the insect's body from 

 previously visited flowers; and (3) the dusting of new pollen 

 on the insect, which will function in pollinating flowers 

 subsequently visited. Experiments and observations both by 

 the writers and by other investigators indicate that prac- 

 tically no seed is produced if the flowers are not exploded. 



It is quite well known that the explosion of alfalfa 

 flowers may be accomplished by other means than insect 

 visitation. The insertion of a more or less pointed 

 instrument into the throat of the corolla has often been 

 resorted to in studying the exploding mechanism of 

 individual flowers. Itoberts and Freeman describe a method 

 of exploding flowers in large numbers by rolling the head 

 carefully, but firmly, between the thumb and the first and 

 second fingers. This exi)lodes the flowers then at the proper 

 stage of maturity. Exploding on a still more whole.sale 

 scale may be done by grasiiing the entire plant between the 

 hands at successive intervals. In this case, it is best to 

 work from the Ijottom toward the top of the plant, exerting 

 the required pressure at the proper spaces. It has been 

 found that flowers exploded by any form of manipulation 

 set seed readily, while other flowers left unexploded, and 

 from which insects are excluded, rarely set seed. 



As only a slight pressure on the keel is necessary to 

 explode the flower, artificial methods may be resorted to as 

 a means of supplementing the natural process as accomplished 

 by insects. In an experiment at the Arlington Experi- 

 mental Farm, in which the method mentioned of exerting 

 pressure successively over the whole plant was used, the yield 

 of pods was increased 2-5j per cent, over that of adjoining 

 rows not thus treated. At Chico, California, an increase 

 of 129 per cent, in the number of pods resulted. Although 

 greater seed yields also result, two experiments at least 

 indicate that the increa.se in the number of seeds is not in as 

 high proportion as is the increase in the number of pods. 

 Further experiments, and more exact observations under 

 varying conditions in diflerent sections, will be necessary to 

 determine just when sutticiently increased yields of seed may 

 be expected to justify the expense of the undertaking. Any 

 alfalfa seed producer may test this method experimentally on 

 a small scale. 



It is recommended that the selection of desirable plants 

 •tommence as soon as the preliminary sowing has developed 

 plants large enough to show their value. The field should 

 be inspected row by row, and seed of the selected plants 

 should be gathered in advance of the regular harvest. The 

 relatively small quantity of seed secured in this way should 

 be sown with great care, to make it cover the greatest possible 

 area of ground. The plot of alfalfa, thus secured, will produce 

 seed of much greater value than that obtained from unselected 

 plants. If this method is carried out, materially increased 

 crops of seed may be secured without detracting from the 

 hay value of the strain. Indeed, both the hay and the seed- 

 producing capacity may be increased by the process. 



