Decomposition of Sweet Clover as a Green Manure 139 



It is noted that in each period there were four pots treated alike as regards 

 liming, and that at harvest the crop was removed from two of these pots 

 and turned under in the other two. It is natural that nitrification should 

 have occurred in all the pots, with the possible exception of the unlimed 

 ones, due to the favorable conditions maintained. 



The original soil contained 57 parts of nitrate per million on the 

 moisture-free fine basis, or 53 parts per million in the dry soil as put 

 into the pots. Thus by noting the figures for nitrates at harvest it is 

 seen that there was an increase during the period of growing the crop, 

 an increase more marked in the limed pots. In table 4 it is shown that 

 in the unlimed pots the nitrates did not increase in the four months 

 following harvest. It may be assumed that decomposition occurred to 

 some extent, as evinced by the fact that at the end of the period the 

 plant material, with the exception of a few roots, could not be distinguished 

 in the soil, but that conditions were not right for complete decay. In 

 table 5 it is seen that following harvest the nitrates increased somewhat 

 in the unlimed pots from which the crop was removed, and that there 

 was a decided increase in the pots in which the material was turned 

 under. Nitrate formation was much greater in the limed than in the 

 unlimed pots. 



The examination of the original soil placed in the pots when the culture 

 experiments were started indicated that conditions had been unfavorable 

 for decomposition processes to go on. It may be considered that the 

 physical conditions and the water relationships for the soil in the pots 

 were more favorable for decay than the conditions obtaining in the field 

 from which the soil was taken. However, a comparison of the results 

 obtained for the limed and the unlimed pots indicates that lime was the 

 larger factor in bettering the conditions favoring decomposition, due to 

 its effect in producing a more favorable medium for the activity of micro- 

 organisms. 



A study of tables 4 and 5 shows that the results vary rather widely 

 in duplicate pots, and makes evident the sensitiveness of nitrate formation 

 to slight variations even under accurately controlled conditions. In the 

 discussion at the end of this paper the probable errors of the results are 

 computed, in order to show how large variations may be expected under 

 the conditions of these experiments. 



season of 1916 



The experimental work conducted in 19 14 was repeated in part m 

 1 9 16. The data obtained in the first season indicated that, from the 

 standpoint of amount of available green manure produced, the four- 

 months period gave the best results. Consequently, it was decided to 



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