Dec. 2 4 . i9i7 Decomposition of Green and Stable Manures in Soil 685 
position of organic matter. This of course has both a beneficial effect and 
a harmful effect from a practical standpoint. The greater rate of decom¬ 
position of the manure causes an increase in the rate of the making 
available of the plant food. It no doubt causes an increase in the rate 
of the destruction of possible toxic substances and probably in itself 
increases the air circulation in the soil. The harmful effect is the deple¬ 
tion of the organic matter in the soil, but since the main benefit derived 
from the organic matter of soil is its enhancement of microbial activity, 
anything within limits which aids in this activity is desirable. 
Columns 9 and 10 (Table III) give the number of pounds of carbon 
lost from the added manure and the percentage loss, respectively. The 
most noteworthy thing in this connection is the large percentage of the 
green manure lost as compared with the stable manure. Thus, it is seen 
that 49 per cent of the carbon of the oats are lost, 60.8 per cent of that 
of the clover, and only 4.23 per cent of that of the manure. It seems 
surprising that about half of such an application of green manure would 
be lost in less than two months. It is believed that probably a somewhat 
comparable loss would take place in the field, because except for a lack 
of drainage these soils were held under conditions not greatly unlike 
those in the field. As to why, in the case of the stable manure in soils, 
a somewhat smaller amount of the manurial carbon was lost from the 
limed than the unlimed soils, we can not state. No doubt our assump¬ 
tion that the amount of carbon lost from the original soil organic matter in 
the manured soils is the same as that from the soil organic matter in the 
unmanured soils is not strictly true. As the manurial organic matter is 
more easily available, it is, no doubt, attacked largely at the expense of 
the soil organic matter. On the other hand, an enormous number, and 
doubtless a very great variety, of bacteria are introduced with the 
manure which of themselves serve to enhance the rate of decomposition 
of the organic matter and, hence, make a comparison of the manured, 
limed, and untreated soils of questionable significance. However, to 
arrive at some conclusion as to the amount of manure consumed in an 
experiment like this, some such an assumption must be taken. From 
column 11 (Table III) it is seen that in every case where total organic 
matter is considered, a larger percentage is decomposed from the limed 
than from the respective unlimed soil. 
In column 12 (Table III) it is observed that the addition of stable 
manure has increased the rate of decomposition of the green manures to 
a small extent. According to some agriculturists, a dressing of stable 
manure on green manure before plowing under serves to enhance the 
rate of decomposition of the latter because of added bacteria. This 
experiment seems to confirm that belief. In anticipation of the consid¬ 
eration of the next experiment, it may be stated here that this result was 
not entirely confirmed when conditions were kept more typical of field 
practice. 
