[SHUTT] NITROGEN ENRICHMENT OF SOILS 125 
NITROGEN-ENRICHMENT OF SOIL DUE TO GROWTH OF CLOVER 







| Nitrogen 
Date of 
Collection | Percentage in | Pounds per 
| Water-free acre 
| Soil Depth of 4” 
| 
Before experiment.............. 13-5-02 -0437 | 533 
After twO Yeats. Ie 14-5-04 -0580 708 
After four yearsen s).). ete. 15-5-06 -0608 742 
Abe Ve years ee ar: acl 30-5-07 | -0689 | 841 
After SIX years Ce 23-5-08 | -0744 | 908 
After seven years............... 4-5-09 -0750 915 
After nine Years. ee. en ve 5-5-11 , 0824 1.005 
Increase in nitrogen due to nine | 
MEATS TOME. | LL ice .0387 | 472 

The soil, it will be observed, continues to increase in nitrogen. 
The figures, however, show that the increase has been irregular, un- 
doubtedly due to seasonal differences affecting growth and the dissipation 
of the debris. If we assume that the growth of the clover adds annually 
nitrogen at the rate of 100 pounds per acre (a conservative estimate) , 
the loss due to oxidation during the experiment period almost equals 
the net gain. Though the loss in a very light, sandy soil such as was used 
in this experiment, would no doubt be much greater than in a heavy 
loam, the probability is that under the best systems of farming on clay 
loams there is a greater dissipation of the nitrogen and humus than we 
have hitherto realized. The data from the Indian Head investigation 
(a heavy clay soil), already reported, show the rapid depletion in 
nitrogen due to a system involving the frequent fallowing of the land 
with no return of humus-forming material. All this points to the 
necessity of constantly replenishing the soil’s stores of humus and 
nitrogen. | 
Probably there is for every soil a limit to which nitrogen-enrich- 
ment can be carried; the nature of the physical and chemical con- 
stituents of the soil and the general weather conditions and many 
other factors no doubt determine the degree to which this method can 
be profitably pushed in any particular instance. But we have in the 
results of this experiment direct and satisfactory proof of the high 
practical value of clover for this purpose. 
