6 LEGUME INOCULATION AND THE LITMUS REACTION OF SOILS. 



and such sharply contrasted growths of plants may, however, be due 

 to inequalities in the distribution of basic soil elements which react 

 on the microflora. 



During the season of 1908 soil samples were submitted from plats 

 or fields where inoculation experiments were in progress, and over 

 600 of these samples from all parts of the United States have been 

 tested by the litmus-paper petri-dish method. From many co- 

 operators we have as yet received no report upon the results of 

 inoculating with pure cultures. Samples from garden patches in 

 cities were discarded. Rather extensive data have been secured upon 

 the inoculation of three crops, alfalfa, vetch, and crimson clover, 

 growing in soils reacting differently to litmus. While scattering 

 reports are on file regarding red clover, Canada field peas, and soy 

 beans, they are too few to w^arrant conclusions at the present time. 



An arbitrary standard for recording the results of these litmus 

 tests has been determined upon as follows: Red = rose-pink;"^ faint 

 pink = between rose-pink and heliotrope-purple;" unchanged = helio- 

 trope-purple ; ** blue = flax-flower blue.'^ 



According to this standard, as is shown in Table II, soils of various 

 types and from various regions, but all giving the red reaction and 

 not limed or manured, have in no case allowed the successful inocula- 

 tion of alfalfa. Almost the same is true of the soils giving the faint 

 pink reaction. It should be noted that the successful case at Timber 

 Valley is perhaps fundamentally different from the others because of 

 the difference in planting. At best, the success is but 25 per cent. 



Those soils which leave the color of the litmus strips unchanged 

 have allowed successful inoculation of alfalfa in twenty out of twenty- 

 five cases. The success here is 80 per cent. 



Still better results are show^n in soils which distinctly blued the 

 litmus; all of the ten cases of such alfalfa inoculation are successes. 



The table also indicates that soils which redden litmus may still 

 allow successful inoculation of alfalfa if treated with lime or manure. 

 Diflerent fields are reported in the table, and there is therefore a pos- 

 sibility that conditions aside from the application of lime or manure 

 determined the success or failure of inoculation. From a careful 

 study of the table in question, however, the inference seems unavoid- 

 able that liming or manuring those soils which redden htmus is usualh' 

 desirable '' from the standpoint of alfalfa inoculation. Unfortunately, 

 at the present time there is no laboratory method of determining how 



a Ridgway, Robert. A Nomenclature of Colors. 1886. 



b ^Miether it is always desirable to apply lime or manure is not certain, for at least 

 in some cases liming or manuring did not prevent soil samples from reddening litmus, 

 yet the inoculation of the field was successful. Further investigations upon this 

 point, as well as upon the biological changes in the soil brought about by applications 

 of lime or manure, must be left for future work. 



[Cir. 71] 



