Apr. 15, i9i8 Soil Acidity as Injiuenced by Green Manures 187 



As to nitrates, the accumulation did not reach so high a point during 

 the time of the experiment with the air-dried manures as with the fresh. 



In general, the evidence indicates that none of the major fermenta- 

 tions here concerned progressed as rapidly with the air-dried as with 

 the fresh materials. Wollny ^ has observed a like decrease in the rapidity 

 of fermentation with fresh plants air-dried and remoistened. 



ORGANIC MATTER OF MANURED SOILS 



The quality of sourness, or acidity, is sometimes traceable to the 

 condition of the mineral constituents of soils sometimes to that of their 

 organic constituents. In the case of the soil used for these experiments, 

 the factors conditioning its acid or lime-requiring qualities have not 

 been at all completely worked out. 



It is, however, a silty soil rather than one rich in clayey constituents, 

 and on the fertilizer plots, other than those treated with ammonium 

 sulphate, has not exhibited a high-degree lime requirement, though, 

 elsewhere in the vicinity, when under grass for a long time or even long 

 farmed by the common rotation, it gradually acquires acid properties. 



In the case of the present experiment, however, the diflferences 

 exhibited as the result of the addition of manures chiefly composed of 

 organic substances must be due, either directly to the fermentation 

 residues of these manures or indirectly to changes they induce in the 

 soil constituents, organic or inorganic. 



To gain some idea of some of the relationships of the organic residues 

 from the green manures, the several mixtures were each thoroughly 

 remixed, passed through a sieve of 40 meshes to the inch, and submitted 

 to additional analvtical examination. 



ORGANIC MATTER 



The amount of the organic matter in the soils was approximated by 

 ascertaining the loss in weight which they exhibited upon burning, 

 correction being made for the portion of this loss that is due to the 

 hygroscopic moisture of the respective soils. 



It is recognized that the method of determination here used gives too 

 high direct results, owing to the fact that the water of hydration of the 

 mineral matters, the carbon dioxid of the carbonate, part of the sulphur 

 of the sulphids, and part of any chlorin present probably escape with 

 the gases formed from the burning of organic matter. We are here 

 chiefly interested, however, in differences in mixtures resulting from the 

 use of a single soil as the chief constituent, of which mixture it constituted 

 slightly over 98 per cent of the dry matter. These diff'erences are not, 

 it is believed, considerably affected by the sources of error just named. 



1 WOLLN'Y, Ewald. DIE ZERSETZUNGEN DER ORGANISCHEN STOFPB UND DIE HUMUSBttDUNGEN. p. 



115. Heidelberg, 1917. 



