122 EXPERIMENT STATION RECORD. [Vol. 40 



made at Rothamsted during the period of 1906-1911, inclusive, in a study of 

 the influence of sugar and plant residues upon nitrogen fixation in both sand 

 and soil and upon the loss of nitrates in the soil. The results are summarized 

 as follows : 



" The foregoing experiments give definite evidence, corroborative of the 

 work of Koch. Remy, and others, that the nitrogen content of sand or soil 

 may be appreciably increased by the activity of Azotobacter when some suitable 

 source of energy is supplied. For this purpose sugars, such as dextrose and 

 saccharose, are suitable, but distinct gains have also been obtained by the use 

 of plant residues. In laboratory experiments an Increment of upward of 6 

 mg. of nitrogen per jrram of plant residues occurred, but in pot experiments 

 gains of 9 mg. per gram of substance were obtained. It is also shown that 

 on the field scale, and in spite of the entrance of complicating factors, definite 

 increases of crop (equal to 20 to 54 per cent) resulted from the application 

 of carbonaceous compounds (sugar) when the soil conditions were favorable. 



"Since the difference between the action of susar and plant residues is 

 largely one of degree and not of type, it is reasonable to suppose that such 

 substances as stubble, leaves, anil other complex organic materials may a s-> 

 serve to contribute Indirectly to the reserves .,f soil nitrogen. The general 

 soil conditions making for the successful operation of nitrogen fixation pro- 

 cesses are, in addition t<> the supply of some source of energy, a suitable tem- 

 perature, the presence of phosphates, and a supply of basic material, such as 

 calcium carbonate. Even under the most favorable circumstances for nit! 

 fixation there occurs a period during which adverse processes come into pay, 

 and it is not advisable that a crop be introduced before these have run to 

 completion. Under unfavorable conditions, and particularly during periods of 

 low temperature, these adverse changes may persist without any subsequent 

 entrance of soil gains." 



The production of carbon dioxid by molds inoculated into sterile soil, 

 U. S. POTTKB and II. S. Snydk.i; (Soil ScL, 5 {1918), No. J. pp. 35V-3T7. ftffS. 5). — 

 This paper, a contribution from the Iowa Experiment Station, describes In- 

 vestigations planned to determine the physiological activity of certain molds 

 when inoculated into sterile soil. A clay loam soil with a lime requirement of 

 1.540 lbs. of calcium carbonate per acre of L\i>00,000 lbs. (Yeltch) was em- 

 ployed. Sterilization was accomplished in the autoclave, and also in the 

 Arnold sterilizer, in an effort to render the soil sterile without radically 

 altering its composition. Inoculations were made from pure cultures of the 

 different molds studied, including Mucor, Rhizopus, Aspergillus, Trichoderma, 

 and Chaetomlum, and from a soil emulsion, and the relative activity of the 

 organisms was measured by the amount of carbon dioxid produced. The cul- 

 tures were made both with and without 1 per cent of dextrose and with and 

 without sufficient calcium carbonate to supply an excess of 1.6 tons of lime 

 per acre over the lime requirement of the soil. The data are presented in 

 tabular form and fully discussed. 



Although the results of 'these experiments are not regarded as having defi- 

 nitely shown that molds are active in normal soils, the fact that in some 

 cases more, and in all cases nearly as much, carbon dioxid was evolved from 

 sterilized soils inoculated with molds as from similar soils inoculated with 

 soil emulsions is held to indicate that they may be. f 



It has been definitely concluded that typical soil molds inoculated into 

 sterilized soil grow with a vigor equal to or nearly equal to the growth induced 

 by an inoculation with the entire soil flora, the evolution of carbon dioxid 

 being the measure of the vigor of growth. Where dextrose was added to the 



