53 
It will be seen that the 39 samples tested gave quite uniform 
results, since in practically every case the availability of the nitro- 
gen was about equal to the percentage of the total nitrogen present 
as ammonia plus nitrate. The average percentage of total nitrogen 
present in the guanos as ammonia and nitrate was 19.6 per cent, 
while the average availability of the total nitrogen was 20.4 per cent. 
Evidently in nearly all samples only a very small portion, if any, of 
the organic nitrogen was available during the 40 to 50 days of the 
tests. This low availability of the organic nitrogen can not be 
attributed to the fact that the soils used were poor mediums for the 
decomposition of organic nitrogen, since dried blood gave an average 
availability of 71, a very fair value for the duration of the tests. 
Even the samples of more or less fresh bat manure, Nos. 472, 503, 
780, 854, 881, 885, and 977, showed practically none of the organic 
nitrogen available during the tests. 
The fact that only the ammonia and nitrate nitrogen and none 
of the organic nitrogen was available in 40 to 50 days does not mean 
that the organic nitrogen in the guanos will not become available 
later. It is evident, however, that the organic nitrogen is very 
slowly available. The fact that insect remains, which form the 
more slowly decomposing part of the organic nitrogen of bat guanos, 
are known to decompose in the soil shows that the organic nitrogen 
is eventually available. Also the fact that, in caves where fresh bat 
manure is being formed, the surface inch of material often contains 
only 2 or 3 per cent nitrogen, shows that the decomposition of the 
nitrogenous compounds is fairly rapid under certain conditions. 
Experiments were made to determine how much nitrogen in bat 
guanos was available in 100 and 140 days, as compared with the 
amount available in 40 to 50 days. Unfortunately, in these tests 
increases in the crop through nitrogen fertilization were not large 
enough to yield reliable results. It is significant, however, that in 
nearly every case the guanos which had remained in the soil the 
longer time gave slightly greater yields. If possible, this work will 
be repeated later. 
In using bat guanos as fertilizers, it should be considered that 
part of the nitrogen (that present as ammonia and nitrate) is imme- 
diately available and that the remainder probably does not begin 
to become available for four months or more. Many guanos, how- 
ever, contain 50 to 90 per oent of their nitrogen in the immediately 
available form. 
VALUATION OF GUANOS. 
In Tables III and IV, a money value per dry ton was given for each 
guano. This value was estimated as follows: The available phos- 
phoric acid was taken as worth 5 cents per pound. Where vegeta- 
