SOIL INOCULATION 819 



ents, especially phosphates and potassium salts; (4) soil moisture and 

 aeration. In addition to these, certain specific treatments may prove 

 to be useful for the control of specific microorganisms, as presence of 

 available carbohydrates for the stimulation of non-symbiotic nitrogen 

 fixation; a certain reaction, for the control of specific plant diseases; 

 soil sterilization, for the improvement of the physical and chemical 

 conditions of the soil and the elimination of certain injurious microor- 

 ganisms. 



When the soil is to be inoculated with certain microorganisms, one 

 may choose between the use of (1) soil, in which the desired crop has 

 been grown successfully; (2) pure cultures, or artificially prepared 

 mixed cultures; (3) specific vigorous strains, which are more active 

 than those already present in the soil. 



Legume inoculation. 2 The first inoculation test on record is the 

 experiment carried out in 1887 at the Bremen Experiment Station. It 

 was found that a good stand of clover was obtained on newly drained 

 heath or swamp soils inoculated with old soil in which clover was grown, 

 provided the swamp soil was limed properly. In comparing the use of 

 soil, in which the specific legume was grown, with pure cultures, for 

 inoculation purposes, it is often found that soil gives better results. 

 Hiltner 3 suggested that this may be due to the fact that, when the seed 

 germinates, certain toxic substances pass out from the embryo which 

 seem to be toxic to the bacteria ; this danger can be obviated by inoculat- 

 ing the soil directly rather than the seed. 



Atwater and Woods 4 were among the first in America to show the 

 favorable effect of inoculation on the growth and nitrogen content of 

 alfalfa and peas. The gain in nitrogen was proportional to the number 

 of nodules on the roots. Warington 3 soon demonstrated that the 

 growth of properly inoculated legumes resulted in an increase in the 

 nitrogen content of the soil; part of a wheat field seeded to clover con- 

 tained 0.156 per cent nitrogen and only 0.142 per cent was found in 



2 A. detailed review of the earlier literature on legume inoculation is given by 

 K. F. Kellerman. The present status of soil inoculation. Centrbl. Bakt., II, 

 34: 42-50. 1912. 



3 Hiltner, L. tlber die Impfung der Leguminosen mit Reinkulturen. Deut. 

 landw. Presse, 29: 15, 119. 1902. 



4 Atwater, W. O., and Woods, C. D. The acquisition of atmospheric nitrogen 

 by plants. Storrs Agr. Exp. Sta. Rpt. 1889-90, 11-51. 



6 Warington, R. The circumstances which determine the rise and fall of 

 the nitrogenous matter in the soil. U. S. Dept. of Agr. Off. Exp. Sta. Bui. 8, 

 22-41. 1891. 



