78 the fakmkhs' handbook. 



th3 plant in a form in which it can be readily assimilated. The process is 

 either symbiotic or parasitic, and is quite distinct from the fixation of nitro- 

 gen by the free-growing organisms, and explains the enormous gain in 

 nitrogen found to result by the growing of a crop of clover or peas. The 

 growth of such a crop, even if not turned under, enriches the soil in nitrogen 

 by the production of ibese nitrogen-fixing bacteria. 



Pure Cultures of Nodule Organisms for Use. 



Many attempt? have been made to prepare cultures of these organisms, 

 for use in directly inoculating either the seed or the soil. The best-known 

 of these was a preparation originally prepared by Professor Nobbe, and 

 known as " Nitragin," which has been in use for many years, and which con- 

 sisted of gelatine cultures of these organisms. Its use was not attended by 

 universal success, and many attempts have been made to prepare by other 

 methods cultures of these organisms which shall possess greater vitality and 

 be of more universal practical application. The best known of these in 

 recent years have been prepared by Professor Hiltner, in Germany, by Dr. 

 Moore, of the United States Department of Agriculture, and by Professor 

 Bottomley, of London. 



Reports of exact experiments conducted with these cultures in England, 

 Canada, and South Africa, show that it is premature to claim for them 

 anything like certainty in ordinary farm practice. Our own experiments 

 with Dr. Moore's cultures, both in pots and in the field, have likewise yielded 

 disappointing results, and the fact is forced upon us that the reports of the 

 remarkable results alleged by the American magazines to have resulted from 

 their use have been much exaggerated. It is always quite possible that some 

 method of preparing these cultures will be devised by which the vitality of 

 these organisms may be retained and their use made of practical value for 

 farm-work. 



Artificial Fixation of Atmospheric Nitrogen. 



The free nitrogen of the air can then be utilised in the manner above noted 

 by plants for their growth, principally by means of free-living organisms 

 within the soil and by the bacteria in the root-nodules of leguminous plants. 

 A point of the very greatest importance to us is, can we produce artificially 

 this nitrogen absorption ? Can we convert atmospheric nitrogen into a form 

 in which it can be utilised by the plant? The importance of this point is 

 enormous, for nitrogen is one of the essential constituents of the food of 

 plants, and owing to the soluble nature of the nitrates produced by the soil, 

 it is continually being washed out by rain into the subsoil beyond the reach 

 of the plant-roots. Consequently, it is necessary to constantly replenish it, 

 and this is done by manuring. 



Manures such as blood, bone-dust, stable manure, nitrate of soda, and 

 sulphate of ammonia, owe their value to the nitrogen they contain, and 

 onormous quantities of the more concentrated manures, such as nitrate of 

 soda and sulphate of ammonia, are used for this purpose. Nitrate of soda is 

 at present exported from a narrow strip of land east of the Andes. The 

 present export is about 1,500,000 tons per annum, equal to £16,000,000. It is 

 expected that the deposits will be exhausted in 1950. It is not only the most 

 important, but the most expensive of the fertilising ingredients, costing 

 about 9£d. per lb., potash costing about 6^d-, and phosphoric acid about lid. 

 to 2fd., according to its solubility. Latterly various methods of fixing the 

 nitrogen of the air have been devised, and the development may have the 

 most important results in the increase of the yield of farm crops. Nitrogen 

 is one of the most difficult elements to force into combination; it combines 

 directly with only a few elements. 



