August, 1009.] 



151 



Scientific Agriculture. 



1886. These results demonstrated, con- 

 clusively, that leguminous plants were 

 capable, under certain conditions, of 

 obtaining and utilizing nitrogen from 

 the atmosphere. It was further shown 

 that this nitrogen assimilation was 

 dependent upon the production of 

 nodules on the roots of the plants. In 

 later research work it was found that 

 the root nodules were full of bacteria, 

 which were the evident agents by which 

 the free nitrogen was appropriated, and 

 to these the name Pseudomonas radici- 

 cola was given. Other observers have 

 since confirmed the results obtained by 

 Messrs, Hellriegel and Wilfarth. Al- 

 though these have been fully establish- 

 ed, it may be added that the exact 

 details of the whole process by which the 

 nitrogen of the atmosphere is first- 

 assimilated by the bacteria and after- 

 wards taken over and utilized by the 

 plant not yet clearly understood. 



The importance of the whole question 

 is indicated by the large quantities 

 of nitrogen which a leguminous crop is 

 frequently enabled to withdraw from 

 the air, even in the course of a single 

 season, through the agency of the 

 bacteria obtained in the nodules on 

 its roots. As examples, it may be men- 

 tioned that in experiments carried out 

 at the New Jersey Experiment Station, 

 a crop of crimson clover was found to 

 have added over 200 lb. of nitrogen per 

 acre to the land in one year, while trials 

 with velvet beans have shown nitrogen 

 gains amounting to 213 lb. per acre in 

 Alabama, 172 lb. in Louisiana, and 141 lb. 

 in Florida. 



In the light of the knowledge thus 

 accumulated on the subject, the question 

 naturally suggested itself to investiga- 

 tors as to whether the co-operation of 

 leguminous crop and nitrogen-gathering 

 bacteria might not be more extensively 

 utilized in enriching the soil and increas- 

 ing its crop-yielding capacity. With 

 this object, therefore, a number of pre- 

 parations for inoculating the soil, all 

 containing the bacteria Pseudomonas 

 radicicola, have, at different i imes, been 

 placed on the market, and a good deal 

 of experimental work has been carried 

 out in the United States, Germany, 

 Canada, and in England. The value 

 of inoculation under certain circum- 

 stances has undoubtedly been indicated, 

 but, speaking generally, the results 

 have so far— for different reasons — been 

 distinctly less premising than was at 

 one time anticipated. 



So long ago as 1887, some inoculation 

 trials were undertaken in Germany. In 

 this case, the land under experiment — 

 reclaimed moor-land — was dressed with 



soil from a field which had previously 

 borne flourishing legume crops. The 

 results were successful, and eminently 

 encouraging, and the example thus set 

 was speedily followed in many districts. 

 In view of the expense of carting soil 

 over long distances, and of the danger 

 of introducing weeds or plant diseases, 

 this method was, however, soon substi- 

 tuted by the introduction of pure cul- 

 tures of the nitrogen-gathering bacteria, 

 put up in a convenient form for inocu- 

 lating either a quantity of soil, or of the 

 seed about to be sown- 



The first preparation of the kind intro- 

 duced on a commercial scale was placed 

 on the market about 1895 by a German 

 experimentor, Nobbe. It was known as 

 ' Nitragin,' and consisted of pure culti- 

 vations of the Pseudomanas organism on 

 a gelatine medium. 'Nitragin' was ex- 

 tensively tested both in Europe and 

 America, but the results, on the whole, 

 were not at all satisfactory. This failure 

 was generally believed to be due to the un- 

 suitable nature of the medium (gelatine) 

 on which the bacteria were grown, and 

 when this was chauged a greater degree 

 of success was attained. Another scien- 

 tist (Hiltner) brought forward a method 

 of cultivating the bacteria on agar jelly, 

 while Moore introduced the still greater 

 change of sending out the bacteria con- 

 tained in cotton wool, which had been 

 soaked in liquid cultures and afterwards 

 dried. This preparation is added to a 

 large bulk of water, with which the 

 seed to be inoculated is treated before 

 sowing. Moore's preparation was used 

 in a very extensive series of experiments 

 carried out by the United States Depart- 

 ment of Agriculture in 1904. The results 

 were very conflicting, but, on the whole, 

 were unfavourable, although slight in- 

 creases of crop were noticeable in many 

 cases as the result of inoculation. Pro- 

 bably many of the failures noticed were 

 due to lack of skill in preparing, hand- 

 ing, and employing the cultures. Cul- 

 ture preparations are still sent out by 

 the United States Department of Agri- 

 culture, but they are now put up in 

 liquid form, enclosed in hermetically 

 sealed bottles. 



In 1907, Professor Bottomley, of Lon- 

 don, brought forward a new preparation 

 of nitrogen-fixing bacteria for inocula- 

 tion purposes, to which the name of 

 ' Nitro-bacterine' was given. This was 

 tried in numbers of experiments, but its 

 introduction into the soil appeared to 

 have little influence on the yields of 

 the various leguminous crops treated. 

 Sample cultures were obtained by this 

 Department and by one or two estate 

 owners for trials with various crops in 

 the West Indies (including sugar-cane, 



