442 IOWA DEPARTMENT OF AGRICULTURE 



have recently come into the market and have proven quite uniformly 

 satisfactory. Many of the older preparations have been discontinued or 

 remodeled because of their uncertainty. Cultures are now being prepared 

 by growing the organisms alternately on nitrogen-free materials and on 

 the roots of the particular legume, thus breeding the bacteria up to a 

 high state of efficiency. 



The improved method of preparation of pure cultures and the dif- 

 ficulties attendant upon the securing of well inoculated soil in so 

 many cases has made it seem advisable to test some of the cultures 

 now on the market and to compare their value with that of soil. 



IOWA experimenIs 



Two experiments were carried out with alfalfa and one each with 

 cowpeas and soybeans. The cultures used in the tests were "Nitragin," 

 prepared by the Nitragin Co. of Waterloo, Iowa; "Farmogerm," pre 

 pared by the National Soil Improvement Co., Charlottesville, Va.; a cul- 

 ture prepared by the Bureau of Plant Industry of the United States 

 Department of Agriculture; "Nitrogerm," prepared by the H. K. Mul- 

 ford Co., of Glenolden, Penn., and soil obtained from a field where the 

 same legume had previously been grown and well inoculated. 



A cross inoculation of alfalfa and sweet clover was tested and also 

 an inoculation with soil plus a commercial culture. 



These tests were all carried out on one-twentieth acre plots, the first 

 test with alfalfa in 1914, the second on different plots in 1915 and the 

 tests with cowpeas and soybeans also in the latter year. The soils 

 were well supplied with lime in each case and all the precautions nec- 

 essary to secure a satisfactory crop growth were observed. 



THE AILFALFA TEST 



In the first alfalfa test the crop was seeded in the spring of 1913 

 with barley as a nurse crop and the yields obtained the following 

 season. In the second test, the alfalfa was seeded in August, 1914. 

 Three cuttings were made in the case of both alfalfa experiments, but 

 these will not be considered separately here. The total yields per 

 acre in pounds are given for all the crops and also the total nitrogen 

 in the crops in pounds per acre. 



The table on the next page gives the results of the tests, both for 

 yields and for nitrogen present in the crops. 



Tbis table indicates that inoculation for any of these legumes brought 

 about some increase in the crop growth. There were some variations 

 in the effects of the different cultures on the various crops and in the 

 case of the alfalfa, on the same crop when grown on different soils. 



While no definite comparison of the values of the various cultures 

 can be made it may be concluded that all the cultures tested gave uni- 

 formly satifactory results. Inoculation with soil was slightly superior 

 in most instances but the differences were too small to be distinctive. 

 In fact, the relative value of the pure cultures and of the soil is so 

 nearly^ equal that the choice between them should undoubtedly be based 

 on the cost of the cultures and the ease with which soil may be se- 

 cured rather than on the crop yields alone. 



