THIRTEENTH ANNUAL YEAR BOOK— RART XIl 682 



Wliile good stands and yields of alfalfa have been secured on fertile 

 soils without manure, yet yields are in almost every case largely in- 

 creased by its use. On sells of on'y. medium fertility, manure is essen- 

 tial to the greatest success; on soi:s below the average, successful stands 

 are practically never secure;! '\\ithout its liberal use. 



Before the alfalfa plant has established its root system, so as to 

 give it a large feeding area, and before the bacteria have developed in 

 sufficient numbers to make available the unlimited supply of nitrogen in 

 the air, an abundance of available plant food must be at hand. Even 

 after the plant is well established the yieM of hay will be much in- 

 creased by an occasional top-dressing of manure. Manure stimulates the 

 activity of the alfalfa bsctfria and makes it possible for the alfalfa to 

 draw more heavily upon the atmospheric nitrogen. The deep roots of 

 the alfalfa, plant make it possible for it to secure much of its mineral 

 plant food far below the surface, where our ordinary farm crop's roots 

 cannot grow. Old alfalfa fields which are well established probably take 

 but a comparatively sm^all per cent of their plant food elements from 

 the surface soil, since a large per cent of the fine-feeding roots are to be 

 found far down in the sub-soil. 



INOCULATION 



While a majority of the successful stands of alfa.fa in Iowa have been 

 secured without inoculation, yet fewer failures are recorded where the 

 presence of the necessary bacteria was guaranteed by inoculation. Be- 

 sides, the co-operative experiments show that in practically every in- 

 stance where the soil was inoculated, a more vigorous growth resulted. 

 In many cases the difference was the difference between a success and 

 a total failure. Considering the ease and slight expense of inocula,tion, 

 a farmer can ill afford to risk a loss by not inoculating. 



On soils which do not naturally contain these bacteria it is absolutely 

 essential that they be introduced. As there is no way of determining 

 whether these bacteria are in a given soil without attempting to grow 

 alfalfa, the only safe way is to inoculate. A small area may be seeded 

 and inoculated the first year, from which soil may be secured for larger 

 areas in following seasons. There are two methods by which this in- 

 oculation may be secured. 



If soils can be secured from a nearby alfa.fa field, where vigorous 

 plants have an abundance of tubercles on their roots, use 300 lbs. or more 

 of soil per acre, distributing it as uniformly as possible. This work 

 may well be done at the time of seeding. If soil is not available from 

 an alfalfa field, soil from a sweet clover patch may be used. This soil 

 should not be exposed to the sun any more than necessary, and may 

 well be applied toward evening and harrowed in thoroughly at once. The 

 direct rays of the sun soon kill the bacteria. 



Attempts have been made for years to develop pure cultures of bacteria 

 for the different legumes. In the main the results have not been particu- 

 larly satisfactory. More recently, however, two commercial concerns 

 have put out cultures which have met with quite general success; one 



