Miscellaneous Useful Products. 228 



[March, 1910, 



OBSERVATIONS ON WILD LEGU- 

 MINOUS PLANTS. 



(From the Agricultural Neios, Vol. VIII., 

 No. 199, December, 1909.) 

 Some interesting facts are brought 

 forward in Circular No. 31 of the Bureau 

 of Plant Industry of the United States 

 Department of Agriculture, with regard 

 to the way in which virgin soils have 

 gained their high nitrogen content. 

 The following is abstracted from the 

 circular to which reference is made : — 



Many hypotheses have been formed to 

 account for the large stores of nitrogen 

 in virgin soils, but none of these have 

 been entirely satisfactory, It seems 

 to be a well established fact that small 

 quantities of ammonia are collected 

 from the air, by rain and added to the 

 soil ; also, that more or less nitric acid 

 is formed by electrical discharges and 

 added to the supply. Some investigators 

 have attributed the fixation of nitrogen 

 entirely to the latter cause. Recently 

 a number of efforts have been made to 

 show that nonsymbiotic, or independent, 

 bacteria are the chief agents in fixing 

 this element. While it seems certain 

 that some nitrogen is added to the soil 

 by each of these methods, it appears 

 to the writer that there is not sufficient 

 evidence to warrant a conclusion that 

 any one of them has been the most im- 

 portant factor in this work. They do 

 not furnish a satisfactory explanation 

 of the presence of such large quantities 

 of nitrogen in the soil. 



Several experimenters have suggested 

 that wild legumes may have played 

 some part in this work ; they have not 

 generally been considered as important 

 factors. The studies reported in this 

 circular indicate that this subject de- 

 serves more thorough investigation than 

 it has yet received, and that native 

 legumes have been of much more im- 

 portance in this role than has been 

 thought. 



Several years ago the writer raised 

 the question as to whether the native 

 legumes of the prairies were sufficiently 

 numerous to have fixed the amount of 

 nitrogen present. A search for published 

 data on the subject was made, but none 

 were found. Accordingly, in the spring 

 of 1908 a series of investigations was 

 begun, a preliminary report of which 

 is here given. 



The writer had long been familiar 

 with the flora of this region, but was 

 not at all prepared for such results as 

 were found. The average numbers of 

 wild leguminous plants per square yard, 

 that were found, were : ordinary ground 



17, high plains S-Q, and sandhills 8'4. 

 After the grasses (including sedges) and 

 possibly the composites, legumes form 

 a larger part of our flora than does 

 any other group of plants. If these 

 figures are representative, or anywhere 

 near it, it is evident that our farm lands 

 from time immemorial have been grow- 

 ing a full stand of legumes. Seventeen 

 plants to the square yard are enough 

 to fill all the soil with their roots. Most 

 of these plants, such as Amorpha, 

 Kuhnistera and Psoralea, have enormous 

 root systems (and these genera represent 

 the large majority of the prairielegumes). 

 A single plant is often sufficient to fill 

 the soil with its roots for a radius of 

 several feet, as any farmer who has 

 ploughed up Amorpha is ready to testify. 

 The smallest root systems are probably 

 those of Vicia and Lotus, and yet 

 seventeen of these to the square yard 

 would seem to be sufficient to gather 

 a large supply of nitrogen. 



Many examinations were made to 

 ascertain the prevalence of nodules upon 

 different species. Large numbers of 

 tubercles were found on every species 

 examined, and on nearly every indi- 

 vidual except mature Kuhnistera. No- 

 dules are especially plentiful on Psoralea, 

 Astragalus, Acuan, Meibomia, and Lotus. 

 On Lotus the nodules are often almost 

 massed together on the tap-root. Some 

 difficulty was experienced at first in 

 finding tubercles on Kuhnistera, but 

 they are always in evidence on seedlings. 

 On the old plants there is a doubt 

 whether typical nodules are produced, 

 or whether the bacteria are in the small, 

 thickened roots which occur in extraor- 

 dinary numbers, almost in fascicles, 

 especially on roots of the previous year's 

 growth, During the coming season an 

 effort will be made to determine this 

 point. The efficiency of these legumes 

 as nitrogen gatherers does not seem 

 open to question, however, if the uni- 

 versal inoculation of the seedling plants 

 is considered. 



It does not seem that most of these 

 legumes choose the poorer soils, for, 

 in fact, many of them grow much better 

 on rich soil ; but when the soil becomes 

 rich in nitrogen and humus, other plants 

 which do not thrive on poor soil are 

 able to crowd out the legumes. There 

 is good reason to believe that lands 

 that are now richest formerly supported 

 the densest leguminous growths, except, 

 perhaps, where the plant food has been 

 washed down from higher levels. 



Western farmers have been slow to 

 learn their lessons from Nature. Nature 

 on her farm has kept up the production 



