260 FIXATION OF FREE NITROGEN BY BACTERIA 



From the large number of researches instituted on the assimilation of nitrogen 

 by plants, the following example, given by EMIL WOLFF (I.), may be selected, 

 and may easily be repeated on a small scale by the reader for his own information. 

 A number of zinc boxes were filled with 24 kilos. (53 Ibs.) of washed calcareous 

 river-sand destitute of nitrogen, the necessary mineral nutrient substances 

 (P 2 0., SO 3 , K 2 0, MgO) being then added and the seeds mentioned in the follow- 

 ing table sown. A certain number of these boxes contained 0.83 gram of nitrogen 

 apiece in the form of nitre. The total dry matter and total nitrogen in the crop 

 were determined, with the following results : 



This table shows that, in the case of peas and vetches, a high yield containing 

 much nitrogen can be obtained, without the soil (initially destitute of nitrogen) 

 having received any application of this element in the form of manure. Such 

 manuring is consequently unnecessary to these plants. 



The results of these experiments on a small scale are confirmed by the 

 observation of large farmers. Schultz of Lupitz, a land-owner in the Mark 

 (Brandenburg), states that he has gathered 227 kilos, of nitrogen per hectare 

 (about 200 Ibs. per acre) annually from his " lupin meadows," for fifteen years 

 without any nitrogenous manuring. Similar results are reported by Deherain 

 from experiments with sainfoin, by the cultivation of which from 205 to 237 kilos, 

 of (combined) nitrogen were obtained per hectare (180-208 Ibs. per acre). 



For this reason agricultural chemists have termed the Leguminosw collectors 

 or accumulators of nitrogen, and have set them up as a class distinct from all 

 other cultivated plants, the latter being grouped under the name of nitrogen 

 consumers. 



This does not, however, imply that the leguminous plants are averse to such 

 manuring; on the contrary, they readily absorb any nitrogenous food pi-esent in or 

 added to the soil, this food assisting the plant to tide over the stage of nitrogen- 

 hunger. So soon, however, as this period of stagnation is passed, they no longer 

 require nitrogenous manure, and the latter, when applied, does not influence the 

 size of the crop. Practical agriculturists utilise this observation by planting soils 

 which are poor in nitrogen with such nitrogen accumulators (especially lupins) as a 

 first crop, which is ploughed in when sufficiently developed. This constitutes the 

 practice known as green manuring. A field treated in this fashion will then 

 contain a much larger amount of nitrogen (in organic combination) than before, 

 and is rendered capable of properly developing other cultivated plants (cereals, 

 hoed crops, &c.), which, by reason of their high nitrogen requirements, would 

 otherwise have yielded only a miserable crop in such poor soils. 



