YoL. VII. No. 16(;. 



THE AGRICULTURAL NEWS. 



•38:? 



SOIL BACTERIA AND NITROGEN 

 ASSIMILATION. 



Reference has frequently been made in the Agrl- 

 ■caltural N'cics to the great vahie of leguminous crops 

 (i.e., crops belonging to the natural order Leguminosae 

 of which the pea is a well-known e.xamplc) to the 

 planter. This value is largely owing to the fact that 

 .a soil on which such a crop has been grown is, under 

 favourable circumstances, enriched with nitrogen, 

 through the medium of the soil bacteria which live in 

 tiibcrcules frequently noticeable on the roots of the 

 leguminous y)lants. These bacteria find nourishment 

 in the juices supplied by the plant, and through the 

 energy supplied by this means, are able to assimilate 

 •or ti.K nitrogen directly from the atmosphere. The 

 nitrogen so h.-ced is in part appropriated by the plant 

 and built up into its tissues, but a good proportion 

 remains behind in the roots on the removal of the 

 green poition of the crop, and largely increases the 

 stock of nitrogen in the soil which is available for the 

 following crop. In e.xpeiiments carried out in the 

 United States it has been estimated that as much as 

 122 It), of nitrogen, equivalent to about 800 lb. of nitrate 

 of soda, is, under favourable conditions, taken from the 

 air and addc<l to each acre of soil, as the result of grow- 

 ing a leguminous crop. 



In addition to the organisms associated principally witli 

 the roots of leguniinou.s crop.s, there is another class of .soil 

 bacteria that can also fi.v atmospheric jiiti-ogeii. These are 

 not associated with any particular crop, and are able to obtain 

 the carbohydrate material necessary for their existence and 

 activities from the humus or decaying vegetable matter in 

 the soil. These independent forms of soil bacteria are widely 

 distributed, and in warm, well-aerated soil.s, containing al)un- 

 dance of liumus and mineral matter they fix a considerable 

 amoiuit of atmospheric nitrogen. An examination <if the soil 

 of two fields at the Kothanisted Experiment 8uition, England, 

 whicli had been allowed to run wild for jnany years, showed 

 .an acpunudation of nitrogen equal to "280 lb. of nitrate of 

 soda per acre per annum in a field poorly supplied with lime, 

 .and to GOO lb. of nitrate of soda per acre per annum in a field 

 well supplied with Yime. Bacteriological tests showed that 

 the nitrogen-fixing bacteria were present in nnn-li larger quan- 

 tity in the second case. 



In view of the expensive nature of nitrogenous manures 

 such as nitrate of .soda, and suli)hate of anunoina, the planter 

 will readily perceive the value of an agency Ijy wJucli this 

 costly clement is derived directly from the air, and a useful 

 <;rop of green fodder grown on the soil at the same time. 



The soil conditions which the bacteria in ques- 

 tion (and also other bacteria whose work in the soil 

 consists in breaking down complex organic nuitter, and 

 bringing it to a form in which the contained nitrogen is 

 directly available as plant food) find most suitable for 

 the exercise of their activities, are therefore well worthy 

 of attention, and the following notes, taken from an 

 abstract, lately appearing in the LouisuiiKi Flanter, 

 of a German pamphlet which discusses the Souritesand 

 Uses of Nitrogenous Manures, relate to these points 

 among others : — 



Of the various constituents of commercial fertilizers 

 nitrogen is undoubtedly the most expensive. Not a little skill 

 and intelligence are required on the part of the agriculturist for 



placing before the growing crops a ]iro])er supply of nitrogen 

 food in a manner both economical and efficient. The growing 

 cost of nitrate of soda, the increasing })roduction of sulphate 

 of ammonia, the more or less successful attempts to manufac- 

 ture nitrogenous materials out of the nitrogen gas in the air 

 and finally, the various .systems of green manuring and 

 tillage are all factors to be reckoned with. The work of soil 

 bacteria is another important factor, and the gain of nitro- 

 gen comjjounds in the soil through the agency of these 

 organisms is very important. A better knowledge of these 

 bacteria must prove of great benefit to every agriculturist, 

 since .such knowledge will enable him to utihze them to the 

 best advantage in providing nitrogen tor his crops. 



Among the conditions which nuist be met in order to 

 render the soil a suitable nKMhuni for the rapid and vigorous 

 growth of nihogen-gatliering bacteria are those of moisture, 

 huuuis, and mineral .salts. It may further be added thaD 

 a sufKcient amount of lime nuist be present for the soil to be 

 alkaline in reaction, since the bacteria cannot flourish in an 

 acid medium. Bacterial life soon comes to a standstill in 

 soils deficient in moi.sture. Similarly, bacteria as living 

 things must ha\-e food, and this they find in great part in the 

 humus. Hence humus is inqiortant not only as a source of 

 food to bacteria, but also in creating conditions favourable fV»i- 

 their development, since the greater the amount of humus, the 

 greater the amount of ;noisture in the .soil, and the greater 

 the amount of moisture, the more rapid the growth of the 

 liacteria. ^Ve should remember likewise, that bacteria are 

 after all only nnnute plants, and as siich they need a supply 

 of available lime, phos[)hoi-ic acid, and potash. Soils poor in 

 these constituents are unsuited for the proper development 

 of bacterial life, and therefore are unsuited for the vigorous 

 growth of crops. 



The need of large (|ua-jtities of mineral plant food is 

 particularly prominent in the case of leguminous crops, crops 

 which form a partnership with bacteria in their roots, and 

 become enabled thereby to draw lavishly on the vast store of 

 nitrogen gas in the air. Crops of cov.-peas, Bengal beans, 

 velvet beans, woolly pyrol, alfalfa, clovers, etc. thus create 

 a supply of nitrogen not only for themselves, but also for the 

 non-leguminous crops which follow and feed on their decay- 

 ing remains. It should be reinend)ered however, that in 

 this process of nitrogen aceumidation by legumes, large 

 amounts of lime, phosphoric acid a.nd potash are used up ; 

 hence the best results in the utilization of atmospheric nitro- 

 gen by leguminous crops can he secured only when anqde 

 jjrovision is made for the supply of the nuneral ingredients 

 of plant food. Repeated experiments have demonstrated 

 that under favourable conditions leguminous crops may c'on- 

 tain 100 to 200 R. of nitrogen per acre, most of it derived 

 from the air. It is thus evident that with an abundance of 

 lime, phosphoric acid, and potash, the accumulation of 

 atmospheric introgen by legumes is only governed liy climatic 

 conditions, and by the nundiers and vigour of the bacteria in 

 the root nodules. 



Packing Rubber Seeds. It is .stated in ibe 



Iiiili't-nihhtr Joiiruiil that favourable re.sults have been 

 obtained at the Singapore Botanic Gardens by packing 

 Para rubber seeds for export in burnt rice husks. The 

 residue from the burnt husks consists of finely-ilivided 

 charcoal, which is sprinkled with water before the seeds are 

 packed in it. Kerosene tins are utilized for packing the seeds, 

 and it is stated that after a journey occupying four months, 60 

 per cent, of the seeds despatched in this way germinated 

 successfully. 



