IRISH GARDENING 



73 



iiotUilt^'W coutaiii the bactt-ria was gathered, from 

 the fact that they (the nodules), like soil extract, 

 possessed, the power of inoculation. They may 

 be regarded, as so nxany jjoints of lodgment 

 wherein the bacteria have taken up their abode 

 (later the entrance of the organism through the 

 root hair was observed under the microscope). 

 Its settlement in the tissue of the root setting up 

 local irritation gives rise to the nodule, something 

 after the manner of li-af-gall formation in the oak. 

 Each nodule b.r.,iiMs a colony. Symlnotic re- 

 lationship is cstaiilislird. between the i)lant and 

 the bacteria : the jjlant sup])lying the sugar, the 

 bacteria providing the valuable ])roteid, through 

 assiniilating the free nitrogen, i)resent in the air 

 spaces of the soil. When the ])lant decays the 

 bacteria escape into the soil, but a great number 

 remain whose activities are linished for good.. 

 By their decay the nodules are enriched in 

 in'oteids, these riches later on becoming part of 

 the soil and adding to its fertility. 



Huch in the main were the results of this re- 

 search. ])erhaps the most interesting and impor- 

 tant of the latter half of the nineteenth century 

 from the agricultural -botani<al ])oint of view. 

 These results were afterwards confirmed and 

 am])lified by English scientists at Hoi liaiupstead, 

 Cambridge, ami •■Iscwhere, and iiian\ further 

 researches have sim-c l)een carried "ut with the 

 view of turning the newly-acquired knowledge 

 to ])ractical use. The hoi)e was at one time 

 entertained that it might be possible to bring 

 about a partnership between the lupin organism 

 Bacillus radicicola and plants other than those 

 of the leguminous order : but all experiments in 

 the way of inoculation of grain, crueifers, &c., 

 have so far proved unsuccessful. Better results 

 have followed in tlic case of inoculation for the 

 beiiclit nf Icgiiiufs thcinsclvcs, more particularly 

 with regard to their growth in newly reclaimed 

 moorhmd. Here the ad.dition of some ordinary 

 soil from olT aral)le land, has been found to be 

 higbly Ijenelicial, as l)y tliat means the organism 

 Bacillus radicicola is, no doubt, introduced into 

 a soil where it had not ]>reviously been in 

 existence. To avoid this cumbersome method of 

 inoculation by quantities of soil taken off arable 

 land, pure cultures of B. radicicola were placed 

 on the market, with special strains appropriate to 

 each of the different leguminous crops — peas, 

 beans, lupins, vetches, <S:c. — but from one cause 

 or another these special cultures have not proved 

 a commercial success. More research seems 

 necessary. Soil bacteriology is, as it were, a 

 science still in the making : it has not yet 

 " arrived " so far as practical agriculture is 

 concerned- 



-Much ])ractical use is, however, made of the 

 hipiu croj) in the reclamation of poor sandy soils. 

 Instead of removing the crop it is ploughed in 

 while still growing. The carbonaceous matter 

 thus added., though of no value chemically as 

 food, is of great im])ortance i)hysically in improv- 

 ing the texture of the loose sand,y soil, imparting 

 1<> it a greater capacity for retaining moisture, 

 ahsoibiug gases. A;c. ; and- of course, tliere is also 

 ad.ded til.- valuable nitrog<-u, in the lixing of 

 whiih lupin excels all the other ieguminosa*. 



Another mici-o-oi-ganism which can assimilate 

 free nhrogen has recently ( I i)() 1 ) been found in 

 the soil, not living in ])art nershii* with a plant, 

 as B. radiclcolii does, but leading an indei>eiul.ent 

 exi«ten<'e, obtaining its carbonaceous food, from 

 dead organic matter in the soil. The activity of 

 this organism (known as A-Jololxnlrr) is now 



associated with the great fertility jiossessed by 

 prairie soils. The growth of grass and the non- 

 removal of the crop even for countless years 

 would in itself only add carbonaceous matter to 

 the soil ; as the grasses have no root nodules, no 

 working alliance with nitrogen organisms, like 

 the legumes. The Azotobacter, however, nuxkes 

 up for this want by using the energy of the 

 decaying prairie vegetation to add the invaluable 

 nitrogen compounds. The im])ortance of these 

 lowly organisms becomes more and more a]»])arent 

 as we go on. Even ordinary farmyard manure is 

 of no use to the crop until certain bacteria liave 

 worked chemical changes in its constitution — 

 until, in fact, its nitrogen compounds have been 

 reduced to amnxonia, to take a particular examitle. 

 If these decomi)osing bacteria are held u]» in their 

 work, or inhibited in any way, the cro]) suffers. 

 Recent ex])eriments at Rotham])stead have shown 

 how these useful bacteria are i)reyed u|)on by 

 other organisms in the soil to the great detriment 

 of the growing cro]). There are therefore both 

 good and bad organisms from the farmer's i)oint 

 of view. Finally, as an instance of a wasteful 

 process going on in the soil, the activity of another 

 organism may be referred to, an activity which 

 sets nitrogen free from ammonia, thus reversing 

 the action of Azolobacler and B. radicicola. It 

 nxay be worth mentioning that this wasteful 

 process is most in evidence where intensive 

 cultivation is carried, on, where in fact the 

 ordinary processes of plant nutrition are speeded 

 up beyond the normal limit. 



In following up our inquiries as to the nianner 

 in which plants obtain the nitrogen of their food, 

 we have had to touch on the question of soil 

 bacteriology — a subject about which the writer 

 does not claim to possess any special technical 

 knowledge. Although in its nature somewhat 

 elusive and intangible, nevertheless the subject 

 appears to be one Avith a future. One of our <;reatesi 

 authorities on questions of practical agriculture, 

 but more especially on all matters ))ertaini)ig to 

 the soil, Mr. A. D. Hall, in his book. " The Feeding 

 of Crops and Stock," says : — " While we are very 

 far from being able to control the bacteria and 

 other organisnrs present in the soil, we are 

 beginning to realise both the fundamental 

 imijortance of the part they play and the manner 

 in which they can be affected by y>rocesses and 

 materials applied to the soil ; and though so far 

 we have only succeeded in exjjlaining results 

 which the practical farmer had arrived at by 

 exj)erience. yet our knowledge nuist in time lead 

 to deliberate and conscious advance in the way 

 of utilising their powers to better effect." Some 

 years later, in the light of further research, he 

 .speaks in a nrore confident tone. In a paper read 

 at the Koyal Institution. May, 1912, he says :— 

 " The problem before us is to bring the iioW 

 bacteria under contnd. and, already we begin to 

 see such control is not im])ossible. . . By 



certain ])rocesses of jiartial sterilisation we can 

 eliminate organisms which keep in check Iho 

 useful bacteria, in the soil — i.e., those which break 

 down the nitrogen coini>ouruls to the state of 

 ammonia. . . . At i)resent the )>rocesses have 

 not been extended to the open held, but there is 

 promise of a nu'thod by which ultimately the 

 unseen fauna and flora will be domesticated, the 

 useful races encouraged, the noxituis rejiressed : 

 just as the larger flora and fauna liave been 

 reduced to our service since the days when 

 l)rimitive nuin lirst turned from Jiuiiting to 

 agri.ulture.-' 



