Vot. X. No. 251. 



THE AGRICULTURAL NEWS. 



391 



A DISEASE OF ALFALFA IN 



ITS RELATION TO SOIL 



INOCULATION. 



'^Z':^;£The following details ot a way in which a disease 

 of alfalfa (Medicago aativa) may be spread, through 

 mistaking nodules produced by it on the plants for 

 those containing the true beneficial nodule organism 

 (Pseudomonas radicicola), are taken from Circular 

 No. 76 of the Bureau of Plant Industry of the United 

 States Department of Agriculture: — 



The relative merits of the inoculation of legumes by the 

 pure-culture method and by the scattering of soil taken from 

 old well-inoculated tields have been widely discussed, and 

 both methods have been recommended by this Bureau. In 

 case old soil is used, the tields from which it is secured 

 should be free from objectionable weeds and insect pests, and 

 free from plant diseases. 



From time to time specimens of supposedly well-inocu- 

 lated plants of alfalfa, crimson clover, and alsike clover have 

 been forwarded to the Laboratory of Soil-Bacteriology 

 Investigations with the e.'cplanation that although nodules 

 were produced in abundance the leguminous crop was not 

 satisfactory. In these cases the appearance of the nodule.s 

 was abnormal and the bacteria isolated from them, although 

 resembling the nodule-forming organism, did not have the 

 power of fixing nitrogen in culture solutions, and as a tenta- 

 tive explanation it was suggested (Bulletin 71, Bureau of 

 Plant industry) that this was but an extreme case of 

 pleoniorphism of Pseudomonas radicicola, which could be of 

 no symbiotic advantage to the leguminous host. 



During 1909 the organism occurring in the abnormal 

 nodules of alfalfa was studied more extensively, anj it was 

 decided that this organism represented a new, although not 

 a destructive, disease of alfalfa. Through the courtesy of 

 Drs. Smith and Townsend, a comparative study was made of 

 material furni.shed by the Laboratory of Soil-Bacteriology 

 Investigations, which shovi-ed that the bacteria causing the 

 almormal nodules upon alfalfa were practically identical with 

 those causmg the crown gall of orchard trees. 



Fortunatelj', the difference between nodules produced 

 by the beneficial nodule-forming organism of the legumes 

 and those produced by the crown gall organism is sufK';iently 

 typical to be easily recognized by an experienced observer. 

 Though it may lie possible to confuse these during a hasty 

 examination, it is obvious upon close inspection that the 

 nitrogen-fixing nodule is an outgrowth from the plant root, 

 and that it has no more apparent effect upon the root than 

 has an ordinary branch of the root. The interior of the nodule 

 contains flesh coloured cells full of bacteria, which may be 

 ea.sily seen under the microscope. The crown gall tumour, 

 on the other hand, causes much distortion of the root, fre- 

 quently forcing it to branch into many small roots, which 

 project from the tumour itself. The interior of the tumour 

 is white, and it is difficult, if not impossible, to see any Iiac- 

 teria in any of the cells, even in the most carefully prepared 

 sections of the tumour tissue. . 



The fact that must be emphasized especially in connexion 

 with farm practice is that the excrescences, or tumours, formed 

 on certain legumes by the crown gall organism have occasion- 

 ally been confused with the desiraMe nitrogen-fixing nodules. 

 The use of soil for inoculating alfalfa or clover, if .selected at 

 random, may be a serious menace. In the few years that this 

 matter has been under observation, many records of the ship- 



ping of alfalfa soil infected with crown gall, under the 

 designation of inoculated alfalfa soil, have been obtained. 



coNuLu.siONs. (1) The crown gall organism has been 

 found in tumours somewhat resembling the normal nitrogen- 

 fixing nodules upon the roots of alfalfa, crimson clover and 

 alsike clover. (2) Great care should be taken in using soil 

 or cultures tor inoculating legumes in regions which may 

 eventually be u.sed for sugar beets or for orchards. (3) It is 

 usually possible to distinguish the tumour produced by the 

 crown gall bacteria from the nodule formed by the nitrogen- 

 fixing bacteria by their external appearance. (4) By the use 

 of special media it is possible to distinguish between the 

 bacterium which causes crown gall and the nitrogen-fixing 

 bacterium which forms the desired nodules upon the roots of 

 leguminous plants. (5) It is not known what other legumin- 

 ous crops are susceptible to crown gall infection. It is 

 believed, however, that there is reason to suspect all the 

 clovers. 



THE LIME IN BASIC SLAG. 



The Journal of tlt.e Board of Agriculture for 

 October I9I1 gives the following abstract of a paper 

 dealing with this subject, which appeared in the 

 Journal ofihe Society of Ghemicallndustry, May 15, 

 1911:— 



In a paper by Mr. James Hendrick in the Journal of 

 the Society of Chemiral Industri/, in 1909, it was shown that 

 there is a much smaller percentage of free lime in basic slag 

 than is conmionly represented, and that calcium carbonate 

 is practically absent. At the same time, it was .shown that 

 there is a considerable amount of 'lime available as a base', 

 that is, lime capable of neutralizing acidity in the soil and of 

 acting as a base during nitrification. An attempt was made 

 to measure the available base in basic .slag, chiefly by dis- 

 tilling a solution of ammonium sulphate with the slag and 

 estimating the basicity from the amount of ammonia given 

 off. Ammonium sulphate was chosen on account of its being 

 extensively used as a fertilizer. It undergoes nitrification 

 in the soil, with the production of nitric and sulphuric 

 acids, and in order that its action may not be harmful 

 by rendering the soil sour these acids must be neutra- 

 lized as produced. This paper describes some further 

 experiments on the subject. It was pointed out that 

 when dilute solutions of ammonium salts are distilled, 

 ammonia is given off, and that consequentlj- the am- 

 monia given ofl', in estimating the amount of lime available 

 as a base in basic slag, might not be due to the basic slag. 

 By distillations of ammonium sulphate without basic slag, 

 Mr. Hendrick found that ammonia was given otf, but only in 

 an amount which, when stated as its equivalent in lime, would 

 amount to a very small percentage of the slag. He concludes 

 that the results in the former paper are not materially affect- 

 ed by the fact that ammonia is volatilized when a dilute 

 solution of ammonium sulphate is boiled, but that these 

 further experiments support the conclusion that there is in 

 basic slag a considerable proportion of lime capable of acting 

 as a base in the soil, and that a part of this lime is readily 

 liberated. Distillation with a solution of ammonium chloride 

 provides, however, a better method of determining the avail- 

 able base in slag than distillation with ammonium sulphate. 



Finally, the glass of the vessels used for distillation in 

 experiments on ammonium salts may have a verj' appreciable 

 influence, especially if alkaline solution^ have previously been 

 boiled in the glass. 



