Vot. XVII. No. 430. 



THE AGRICULTURAL NEWS. 



33:? 



BAT GUANOS OF PORTO RICO AND 



THEIR FERTILIZING VALUE. 



Deposits of bat guano are especially common in the 

 tropics and in sub tropical regions, and their fertilizing value 

 has never been investigated thoroughly. Generally they are of 

 small size, consisting ot from a few to several thousand pounds, 

 and they u.sually occur in limestone caves. Results and 

 analyses of an investigation to determine the fertilizing value 

 of ihe bat guano of Porto Rico comprise Bulletin Xo. 2j 

 of the Porto Rico Agricultural Experiment Station. This 

 material is roughly divided into fresh bat manure, decom- 

 posed guano, and leached or phosphate guano. 



The analyses and tests reported show the great variation 

 in difierent bat guanos, in respect to their content of the 

 fertilizing elements, and the availability of the elements. 

 Bat guanos, except fresh bat manure, cannot therefore be 

 regarded as a .specific fertilizer in the .same sen.se as modern 

 commercial fertilizers, or even as the old Peruvian guano. 



The fresh bat manure, however, is a fairly definite 

 material in appearance, composition, and availability of its 

 phosphoric acid. It is 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 of high availability (little less than that 

 of ac:d phosphate), and ihe 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 analysed where practicable, 

 as it is somewhat variable, especially where not freshly 

 gathered. 



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 fer- 

 tilizers 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 oa 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 becau.=e of a low availability of 

 the nitrogen or phosphoric acid. This does not mean that 

 they are capable of utilization only under certain conditions, 

 although they can be used mere 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 particu- 

 larly effective for certain conditions, because of having their 

 nitrogen present in different degrees of availability. 



Most guanos can be mixed with any of the commercial 

 fertilizers without loss of availability in the miiture. A few 

 gJanos containing carbonate of lime should not he mixed 

 ■with sulphate of ammonia or acid phosphate. A test for car- 

 bonate should be made by observing whether the guano 

 effervesces with acid, before mixing a guano with such mater- 

 ials. If it is desirable to use a guano containing carbonati^ 



with sulphate of ammonia, the sulphate of ammonia should 

 be apphed to the soil first, and later the guano incorporated 

 with the soil. ( )n the other hand, a few guanos contain con- 

 siderable ammonium salts, and these should not be mixed 

 with basic slag, as the free lime of the slag will liberate the 

 ammonia. 



Guanos can also be used to supplement stable manure, 

 as stable manure IS relatively deficient in phosphoric acid. 

 A phosphatic guano can be advantageously added to the 

 compost heap as it is being formed. By making the material 

 more compact, this will tend to conserve ammonia. 



Low-grade phosphatic guanos can be mixed with coffee 

 hulls and pulp, which contain a small amount of potash. 

 Doubtless the acetic acid produced in the fermented hulls and 

 pulp will aid somewhat in rendering the phosphates more 

 available. Experiments, however, have not been conducted 

 in support of this conclusion. Composting soluble phos- 

 phatic guanos with waste or decaying citrus fruits and pine- 

 apples, or with refuse from pineapple canneries wr.uld 

 doubtless be quite effective in increasing the availability of 

 the phosphoric acid in such materials. 



In applying the guanos, it should be borne in mind that 

 most of them contain little water-soluble material. Conse- 

 quently they will be most effective when well and evenly 

 mixed with the soil. 



When fresh bat manure, or guanos high in nitrogen and 

 organic matter are to be used for young pine-apples, the 

 material may be safely applied in the crown, as is done with 

 dried blood. Even though these guanos should contain con- 

 siderable ammonia and nitrate, there will be little danger of 

 injuring the plants, a3 the bulky nature of the fertilizer pre- 

 vents dangerous concentration of soluble salts in any place. 

 Only fresh bat manures, or guanos composed chiefly of organic 

 matter, should be applied in this way as other guanos, like 

 •soil, will tend to smother the plant. 



Compounded with other materials, on the basis of their 

 analys's and efficiency to make the proper formula, guanos 

 can be used for any crop. There are some specific fe.itures 

 about the guanos, however, which make them especially good 

 for long-time crops. 



All the guanos contain a considerable portion of their 

 nitrogen in an insoluble and relatively unavailable form. 

 To this part of the 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 therefoie 

 be regarded as of considerable value for a longtime crop, 

 •ir at least for the permanent enrichment of the soil. 



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 com- 

 pleted, quantitative dita should be available concern- 

 ing 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 

 the bat guanos should be particularly valuable phosphatic 

 fertilizers for acid soils and for non-calcareous clay soils. ( )n 

 neutral sandy soils they should show an efficiency equal to 

 that assigned them in this report, but not an enhanced 

 efficiency. Un strongly calcareous soils many guants, in 

 common with bone meal and rock phosphate, will have their 

 efficiency lowered much more than that of acid phosphate. A 

 few guanos, however, appt-ar particularly good for calcareous 

 soils, their efficiency being less affected by liming than any 

 of the other phosphates. Thus far no analytical method has 

 been found which will tell whether nr not the efficiency of a 

 guano will be affected by liming. 



