REPORT OF THE CHEMIST. 141 



SOIL INOCULATION FOR THE GROWTH OF THE LEGUMES. 



THE USE OF NITRAGIN IN AGRICULTURE. 



Though not generally practised as a means of soil enrichment, it has been known 

 for many centuries that the growth of clovers and other members of the Pulse family, 

 now commonly termed legumes, increased rather than diminished the fertility of the 

 soil, so that the yield of grain after a crop of clover was greater than it would have 

 been without a previous seeding of clover. The theory generally accepted was that the 

 clover being a deep rooted plant brought up from the sub-soil mineral matter that was 

 out of the reach of other farm crops. This, however, appears to be but one of the causes 

 — and that a minor one — for the fact above mentioned. The chief reason, as revealed by 

 a recent scientific discovery, lies in the fact that the legumes can appropriate the free 

 nitrogen of the atmosphere, assimilating and building it up into their tissues. This 

 nitrogen, by the decay of the roots (and foliage, if the crop is ploughed under) may be 

 utilized, after the process of nitrification, by subsequent crops. As far as we are at 

 present aware the legumes only have this power, hence they are known as nitrogen-col- 

 lectors in contradistinction to all other crops, which are known as nitrogen-consumers. 

 The demonstration that the free, that is uncombined, nitrogen of the atmosphere can be 

 so utilized by the legumes is due to Hellriegel, a celebrated German scientist. He, 

 with his equally renowned colleague Wilfarth, made this announcement to the world in 

 1886, at the same time giving overwhelming proof of the correctness of the assertion 

 and explaining the way in which this appropriation and assimilation takes place. The 

 discovery was not only a brilliant scientific achievement, but one of the greatest im- 

 portance to the agricultural world. 



In explaining the fact of this discovery and the application to practical agriculture, 

 it may first be pointed out that the legumes have not in themselves the power of free 

 nitrogen assimilation ; in this respect all plants are alike. They can, however, utilize 

 atmospheric nitrogen through the agency of certain micro-organisms present in the soil. 

 These micro-organisms, microbes or bacteria attach themselves to the roots of the 

 legumes upon which nodules or tubercles then form. These contain the microbes. In 

 some way, at present not well understood, the latter can absorb the nitrogen of the air 

 occupying the instertices between the soil particles, converting it into certain nitrogen- 

 ous compounds that enter the sap circulation of the host plant and finally are stored up 

 in the tissues. When the nodules and their inhabitants are not present in the soil, 

 clover, pease and all other legumes must, like the rest of vegetation, obtain all their 

 nitrogen from the supply in the soU existing there as nitrates. 



Now, it is to be noted that these micro-organisms, though very widely distributed, 

 are not found in all soils. The question, therefore, of the possibility of introducing 

 them where absent, or present only in small numbers, becomes one of agricultural im- 

 portance. Further, if soil inoculation (as such a process may be well called) is possible, 

 can it be made an economical method for enriching the soil with nitrogen 1 These are 

 questions that come well within the scope of scientific agriculture to investigate, ques- 

 tions well worthy of careful research, for the answers must be of the greatest importance 

 to farmers. 



It might, at the outset, be supposed that the soil of a field growing a luxuriant 

 crop of clover, the roots of which possess nodules, would in all probability contain large 

 numbers of these organisms. Naturally, therefore, we find the first experiments con- 

 sisted in taking soil from a field upon which a legume possessing an abundance of 

 nodules had been grown and scattering it on the field to be impregnated. This was 

 practically soil inoculation, and though the plan in many instances proved eminently 

 satisfactory, the carrying out of it was frequently costly and cumbersome. Dr. Nobbe, 

 of Tharand, Saxony, was the one who first made this practical application of Hellriegal's 

 discovery. 



