56 
a complete fertilizer, high in nitrogen, medium in phosphoric acid, 
and low in water-soluble potash. The water-soluble potash, of course, 
is all available, the phosphoric acid is ol high availability (little less 
than that of acid phosphate), and the nitrogen is in part immediately 
available and in part slowly available. This material is somewhat 
similar to tankage, differing in containing potash, in having part of its 
nitrogen more available and part less available than the nitrogen of 
tankage, and in containing, as a rule, more immediately available 
phosphoric acid. 
The monetary value of fresh bat manure averages about $33 per 
dry ton. It should be analyzed where practicable, as it is somewhat 
variable, especially where not freshly gathered. 
As fresh bat manure will lose its soluble and valuable constituents 
if exposed to leaching, it is well to extract this material from the 
cave periodically. In Texas some gather the fresh bat manure 
annually. A cave where much fresh manure is being deposited is 
evidently a valuable permanent asset. 
All other guanos, excepting the fresh material, are incomplete 
fertilizers, lacking either potash, nitrogen, or both. All bat guanos, 
however, contain phosphoric acid. As a rule the uncontaminated 
guano increases in phosphate content as the nitrogen content 
diminishes. Most bat guanos are to be regarded as phosphatic 
fertilizers containing a small amount of nitrogen, although some are 
merely phosphatic fertilizers. They ought to be reinforced by the 
addition of other materials before being used for certain crops on 
certain soils. 
Most bat guanos, but not all, are to be classed with the low-grade 
fertilizers, either because of a low percentage of the fertilizing 
elements, or because of a low availability of the nitrogen or phos- 
phoric acid. This does not mean that they are capable of utilization 
only under certain conditions, although they can be used more 
advantageously under some conditions than under others. As 
guanos contain a variety of other substances besides nitrogen, 
phosphoric acid, or potash, some persons have an idea that they 
ought to have a peculiar fertilizing value because of their very 
complexity. This is not true for the most part, although a few of 
the bat guanos, in common with the old Peruvian guanos, are par- 
ticularly effective for certain conditions because of having their 
nitrogen present in different degrees of availability. Most guanos 
contain more or less gypsum. Little importance should be attributed 
to this, since gypsum has proved of fertilizing value only in excep- 
tional cases, aside from its use on soils impregnated with alkali salts. 1 
* The favorable action of gypsum on a few soils has been attributed to the furnishing of lime or sulphur, 
the liberation of potash from soil silicates, and the protection afforded by the calcium ion in antagonism 
between salts. 
