SOILS-^FEETILIZERS. 515 



As regards the aniinoiiificatiou of the organic manures flesh meal, horn meal, 

 and blood meal, the bacterial activity showed, a rise from August to October, a 

 tendency to fall or remain constant in November, and a rise to a maximum in 

 December. This was followed by a minimum in February and. a low maximum 

 in April, and from April to July there was a slight fall, wliich was probably 

 continued to a summer minimum in August. Similar results were obtained as 

 regards nitrification, except that the spring maximum occurred in March and 

 the decline to a summer minimum commenced in April. The slight variations 

 in ammoniflcation and nitrification and the December maximum are attributed 

 to the mild character of the winter. Nitrogen fixation in 1 per cent mannite 

 solution was low with the soil samples of August and September. Subsequently 

 it was fairly constant except with samples taken after plowing. No definite 

 results were obtained in the cyanamid experiments. 



" Comparison of the results of manuring experiments in the field with those 

 of laboratory tests indicates that the latter may be of considerable value in 

 affording information as to the decomposition processes naturally occurring in 

 soils. No difference, however, could be detected between soil from one-half of 

 the experimental area which had received autumn cultivation and soil from 

 the other half which remained untouched until the spring i^lowing, although 

 the crop returns showed a 20 per cent superiority (in respect to nitrogen) in 

 favor of autumn cultivation." 



Solution methods were found to be equal to those in which the natural soil 

 is employed as a medium. As regards nitrification, the solution method gave 

 much clearer indications of seasonal variation, while the seasonal variation in 

 ammonification was more clearly indicated in soil tests. 



Nitrogen fixation by Azotobacter in substrata poor and rich in nitrogen, 

 J. Hanzawa (Centhl. Bald, \_etc.}, 2. AU., Jfl {lOlJf), No. 18-23, pp. 573-576; 

 ahs. in Jour. Chem. Soc. [Lotidon^, 106 {191J,), No. 623, I, p. 1113) .—Fuvther 

 studies along the line of those reported by Lohnis and Green (E. S. R., 31, 

 p. 120), including a test as to the value of humus as a source of energy in the 

 nitrogen fixing process, are reported. 



Mixed cultures of different strains of Azotobacter were found to be more 

 effective in nitrogen fixation than the same bacteria in pure cultures, especially 

 in aqueous solutions of mannitol. 



The nitrogen of humus, even in large quantities, had no serious retarding 

 effect on the fixation of nitrogen by pure cultures of Azotobacter. Small 

 amounts of nitrates also had almost no effect, but when present in amounts 

 corresponding to amounts of nitrogen greater than 2.5 per cent of the carbon, 

 nitrogen fixation was retarded and finally inhibited. It is thought probable 

 that the soil nitrogen can only in special cases, if at all, have an unfavorable 

 effect on nitrogen fixation. 



The humus of stable manure was capable of being utilized as a source of 

 energy in nitrogen fixation, while that of green manure was not. 



Mutual influence of certain crops in relation to nitrogen, K. F. Kellerman 

 and R. C. Wright {Jour. Amer. 8oc. Agron., 6 {1914), No. 4-5, pp. 204-210, figs. 

 4). — A brief account is given of pot experiments with legumes and nonlegumes 

 grown singly and combined which showed " that the effect of a given crop upon 

 two different soils may be very different, both in regard to its effect upon the 

 total soil nitrogen and upon the nitrifying power of the two soils." There was 

 an actual loss of soil nitrogen in the case of the nonlegumes, especially barley, 

 over and above that utilized by the plants. With the legumes there was no 

 such loss, but in some cases a gain. Where combinations of leginnes and non- 

 legumes (beans and barley, and peas and barley) were grown both the legmne 

 and the nonlegume showed an appreciable gain in nitrogen. 



