Relation of strains of nodule bacteria and fertilizer treatments to nodulation and growth of alfalfa

Experiments were conducted in two series of field plats in western Washington to ascertain the inoculating and nitrogen-fixing power of various strains of alfalfa nodule bacteria, their adaptability to a number of soil types in this area, and the effect of various fertilizer applications on nodulation and on the growth of alfalfa. The results of these experiments indicated with few exceptions that seed inoculated according to directions given for the various cultures and planted without a nurse crop at the rate of seeding customary in field practice resulted in satisfactory inoculation of the alfalfa with the large majority of strains of nodule bacteria tested in the various soil types included in these field plats. Although a good stand was secured in all cases, the alfalfa on all of the plats failed to grow satisfactorily toward the end of the first growing season and during the two following growing seasons. The application of lime and commercial fertilizers had no marked beneficial effect upon the growth of the alfalfa in spite of the fact that lime applied alone or in combination with commercial fertilizers caused marked increases in nodulation in the majority of the field plats. Differences in nodulation caused by the various strains of alfalfa nodule bacteria were not sufficiently outstanding to be significant, but marked differences in the first year's growth and thrift of alfalfa were observed in two soil types as a result of bacterial strain specificity. However, this increase in growth and thrift was not sufficiently great or lasting to make the alfalfa on these plats a success in its second and third years. Soil inoculation with nodule bacteria, soil drainage and physical condition, and soil reaction, although somewhat acid in all plats, did not prove to be limiting factors in the growth of alfalfa. Therefore, it was apparent that the available mineral plant food in these soils probably was deficient for successful growth of alfalfa and was not restored by a single but generous application of commercial fertilizers. Repeated fertilization with barnyard manure or green manure crops in addition to liberal applications of commercial fertilizers is suggested as a means of building up the available mineral plant food supply of these soils before seeding them to alfalfa.