270 Bulletin 275. 



The cause of the great difference in yield on the inoculated and the 

 uninoculated sterilized soils is not indicated by anything in the analyses 

 made six weeks after the first infusion was added, unless it is the more 

 rapid decrease in the soluble matter which occurs in the inoculated 

 soil. No later analyses have been made, but probably will be when the 

 wheat following the millet is removed. 



It has been suggested by Russell and Hutchinson CO that, as ammo- 

 nification takes place very rapidl}'^ in partially sterilized soils, while 

 it proceeds much more slowly in normal ones, and as nitrogen never 

 accumulates in salts of ammonium as it does in nitrates, a limiting 

 factor in soil productiveness is quite commonly to be found in the 

 power of ammonification which a soil may possess. The argument 

 is advanced that during the process of partial sterilization the organ- 

 isms which destroy the ammonifying bacteria and thus limit their 

 product are themselves destroyed and that the plants utilize the ammo- 

 nia, which is shown to be produced in very much larger quantities 

 in these partially sterilized soils. In support of this the fact is cited 

 that an infusion of unsterilized soil added to a partially sterilized one 

 serves to- decrease its productiveness. From this it is concluded that the 

 reintroduction into the soil of .the organisms injurious to ammonifying 

 bacteria decreases plant growth by limiting the production of ammonia. 



While our experiments indicate that plants growing on the steamed 

 soils use ammonia, they do not give evidence that the decreased crop 

 production occasioned by the infusion of unsterilized soil was due 

 to lack of ammonia. By reference to Table X i-t will be seen that 

 the steamed soil planted to wheat and treated with the infusion of 

 unsterilized soil contained more water-soluble ammonia and more 

 total ammonia than did the soil not receiving the infusion. At the 

 time these analyses were made, the crop on the infusion-treated soil 

 had already fallen behind the other in growth, as may be seen by 

 reference to Table IX. It would seem, therefore, that in the case 

 of this soil under the conditions of sterilization, etc., to which it was 

 subjected, the depres.sing effect of the inoculation on plant growth 

 was not due to lack of nitrogen either in the form of ammonia or nitrates. 

 We mention this not because it has a direct bearing on the conclusions 

 reached by the investigators referred to, as they were working with soil 

 treated in a very different manner, but because it shows that, under 

 some conditions at least, the effect of an infusion of unsterilized soil 

 depresses plant growth in some way other than by limiting the supply 

 of water-soluble ammonia. 



'Jour. Agr. Sci., Vol. 3, pp. 1 18-12 1. 



