61 
nitrogen, a value only one-fourth that of the ammoniacal and nitrate 
nitrogen, was given. It is nevertheless probable that practically all 
this insoluble nitrogen will become available in time. It should 
therefore be regarded as of considerable value for a long-time crop 
or at least for the permanent enrichment of the soil. 
SOILS ON WHICH GUANOS SHOULD BE USED. 
Work is at present under way to determine the relative efficiencies 
of the standard phosphatic fertilizers on the different soils of Porto 
Rico. When this work is completed, quantitative data should be 
available concerning what phosphates are best for the different soils. 
From the general knowledge available on the subject and from the 
availability tests reported here, it appears that bat guanos should be 
particularly valuable phosphatic fertilizers for acid soils and for non- 
calcareous clay soils. On neutral sandy soils they should show an 
efficiency equal to that assigned them in this report, but not an 
enhanced efficiency. On strongly calcareous soils many guanos, in 
common with bone meal and rock phosphate, will have their effi- 
ciency lowered much more than that of acid phosphate. A few 
guanos, however, appear particularly good for calcareous soils, their 
efficiency being less affected by liming than any of the other phos- 
phates. Thus far no analytical method has been found which will 
tell whether or not the efficiency of a guano will be affected by 
liming. 
SUMMARY. 
Deposits of bat guano are especially common in the Tropics and in 
subtropical regions, and their fertilizing value has never been investi- 
gated thoroughly. Generally they are of small size, consisting of a 
few to several thousand tons, and they usually occur in limestone 
caves. 
The material may be roughly divided into fresh bat manure, decom- 
posed guano, and leached or phosphatic guano, although this classi- 
fication is not sharp. Only the fresh bat manure is of fairly constant 
composition, averaging 10.93 per cent nitrogen, 7.29 per cent total 
phosphoric acid, 5.54 per cent citrate-soluble phosphoric acid, and 
2.3 per cent water-soluble potash. The leached phosphatic guano is 
similar physically and chemically to leached guanos of bird origin. 
Attention was called to the manner in which the different kinds of 
guano were formed and the conditions determining the composition 
of the material and its variation in the cave. 
Twenty-five samples were subjected to a complete mineral analysis. 
No one constituent showed any regular variation with any other con- 
stituent in any sample. The portion of the total phosphoric acid 
