Sept. ii, 1916 



Bacteriological Studies of a Soil 



965 



possible to replace calcium carbonate with manure. The effect of manure, 

 however, can be entirely eliminated by calcium carbonate. As perhaps 

 would be expected, the percentage increases due to calcium carbonate 

 not replaceable by manure are in an inverse ratio to those of manure not 

 replaceable by calcium carbonate. Such increases seem to be, in general, 

 correlated with the type of crop — that is, those crops naturally depleting 

 the soil of organic matter (corn and wheat) show a large percentage in- 

 crease from manure not replaceable by calcium carbonate, while those 

 naturally keeping up the organic matter (rotated) show a larger percent- 

 age due to calcium carbonate not replaceable by manure. 



It seems evident that in a general way the effect of the two agencies 

 are the same, so far as nitrate formation is concerned. This does not 

 support Temple's contention (20) that the beneficial effect of manure is 

 due to organisms actually brought in with the manure. 



Cropping system. 



Percentage of 

 increase due 

 to calcium car- 

 bonate in 

 presence of ma- 

 nure or not re- 

 placeable by it. 



Percentage of 

 increase due 

 to manure in 

 presence of 

 calcium car- 

 bonate or not 

 replaceable 

 by it. 



Corn 



Wheat. . . 

 Timothy 

 Rotation 



39 



21 



o 



9 



It is also interesting to note that in the rotation studied either with or 

 without the addition of calcium carbonate, the effect on nitrate formation 

 of the chemicals has been practically identical with that of the manure. 

 In the case of wheat, chemicals have had only about one-half of the bene- 

 ficial effect that manure has had. As to the effects of the different crops, 

 corn and wheat undoubtedly have a harmful effect in the absence of ma- 

 nure, both ranking very low either with or without calcium carbonate. 

 On the other hand, with the addition of manure they are raised from tenth 

 and ninth places to first and second places, respectively. Timothy and 

 the rotation are approximately equal and very much higher than corn 



