124 Bulletin 394 



and Vinall's bulletin will show. A more valid objection to sweet clover 

 has been the difficulty experienced in obtaining a satisfactory stand, 

 especially the first season. This has been demonstrated to have been 

 due in part to faulty methods of cultivation, for a hard, compact seedbed 

 is required. The difficulty has probably been due in a larger degree to 

 poor germination because of hard seed, especially when combined with 

 lack of inoculation. Further, the fact that sweet clover is a biennial 

 has curtailed its use. Two years has seemed too long a time to give up 

 a field to a soil renovator, particularly as the woody nature of the plant 

 at maturity indicates that it would decompose slowly in the soil. The 

 lack of accurate experimental data has doubtless been another factor in 

 limiting the use of the crop. 



A survey of the factors that have limited the utilization of sweet clover 

 in general farm practice indicates that some exact data are needed 

 relative to the following points: the ability of the plant to thrive on a 

 worn-out soil; methods of increasing the germinating power of the seed; 

 the value of lime; the possibility of securing a satisfactory yield the 

 first season; the rate of decay of the plant material when incorporated 

 with the soil; and the proper time for turning under to combine a satis- 

 factory yield with rapid decay. It was with the object of throwing 

 some light on these questions that the present investigation was undertaken. 



DECOMPOSITION OF GREEN MANURE 



No record has been found of any study of the rate of decay of sweet 

 clover as a green manure. The value of green manures has been more 

 frequently studied from the standpoint of their effect on succeeding crops 

 than by measurements of their rate of decay. This is natural, inasmuch 

 as the decomposition of organic matter is a complex process of many 

 stages and no really satisfactory methods have been devised for measuring 

 it. Decay of organic matter is caused by microorganisms, as first pointed 

 out by Wollny (1884), and this fact has been utilized in the methods 

 devised for studying the process. 



Wollny (1886) measured the carbon dioxide evolved during decay. 

 This method leaves open the question as to the form into which the 

 nitrogen of the organic matter is converted. Inasmuch as plants take 

 up this element principally as nitrate, it is desirable to know to what 

 extent nitrification is going on, or at least to know that conditions are 

 favorable for this process. It is obvious that conditions which favor 

 initial decomposition and those favorable to nitrate formation are not 

 identical. Pagnoul (1895) has shown that under certain conditions 

 ammonium salts may form in abundance while nitrification proper is 



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