54 
tion tests were made with the guano, the amount of available phos- 
phoric acid as shown by the vegetation tests was used in calculating 
the value, rather than the citrate-soluble portion, but where no vege- 
tation test was made, the citrate-soluble phosphoric acid was taken 
as the amount available. It should be borne in mind that the values 
given for guanos which were not tested vegetatively are not so accu- 
rate as those for the tested guanos because of the inaccuracy of the 
citrate method for available phosphoric acid in certain guanos. 
Five cents per pound was allowed for water-soluble potash present 
in guano. This value was taken as being about that prevailing before 
the European war. The present value (1917) is about 40 cents per 
pound; the future value can not be predicted. The temporary value 
of the guanos containing 2 or more per cent of potash is thus consid- 
erably greater than that given in the tables. 
Twenty cents per pound was allowed lor that portion of the nitrogen 
present as ammonia and nitrate. The remainder of the nitrogen is 
very slowly, although ultimately, available. An allowance of 5 cents 
per pound was thus made for that nitrogen not immediately available. 
There were GS samples containing from 0.5 to 1.93 per cent of total 
nitrogen which were not tested vegetatively nor for the solubility of 
the nitrogen in water. Practically all these gave a qualitative test for 
nitrates. A value of 10 cents per pound was assumed for the nitrogen 
in such samples. This value may be a little too high lor some samples 
and too low for others, but the average is considered fair. 
In assigning a value to the guanos, consideration was thus made of 
the immediately available phosphoric acid and potash, and of the 
immediately and slowly available nitrogen. No allowance was made 
for the phosphoric acid which was not immediately available. Pos- 
sibly some allowance should have been made for the insoluble phos- 
phoric acid in guanos containing a high percentage, but the value 
should be low, as only on certain soils will this form of phosphoric 
acid show even a low availability. The value of such insoluble phos- 
phoric acid in Porto Pico will be better established when those soil 
areas are known which respond to insoluble phosphates. In regions 
where finely ground rock phosphate is used as a fertilizer, the in- 
soluble phosphoric acid in guanos should have an equivalent value, 
as the availability will average about the same. On account of the 
low value and efficiency or ground rock phosphate and because of 
freight charges, there has been no market for this material in Porto 
Pico up to the present time, and thia analogy does not establish a 
value here. 
Bearing in mind that the insoluble phosphoric acid would have an 
efficiency only on certain soils, about 1 cent a pound might be allowed 
for the monetary value of insoluble phosphoric acid in guanos con- 
taining an appreciable amount. Certain guanos like Nos. 796, 807, 
