DAT GIAXO IX KIl()J)i;slA. 159 



Occurrence and Mode of Forinctfion. — In almost eveiy 

 instance those caves occur in limestone formation,, and the 

 deposit consists almost entirely of the excreta and remains 

 of bats, Avhicli have inhabited the caves from time immemorial. 

 In some caves the renmins of native calabashes and bones 

 of animals have been found, pointino- to the fact that in 

 some remote age the caves liad been inhabited by native 

 tribes. This fact was ])orne out when I made an inspection 

 of a series of caves in the (latooma district, refeience to which 

 Avill be nuide latei' on. 



If the deposit occurs in a dry cave or caves, and was 

 f(jrmed under the nn)st favourable conditions, the excreta 

 would remain dry and in an unchang-ed condition, and one 

 would ])robably find the bat guano to contain practically all 

 the nitrogen, phosphoiie oxide and potash (jrig-inally jiresent 

 in the manure. 



In a semi-tropical climate such as we have in lihodesia, 

 and where the deposit occurs on limestone formation in damp 

 caves, the rate of decomposition^ (hie to bacterial action would 

 be very rapid, resulting' in the loss of a large anumnt of the 

 (tig'anic nitrogen, the nitrog-en ])eing' converted into volatile 

 ammonium carbonate. Any water percolating- in the caves 

 would leach out the solulde nitrates and other water soluble 

 constituents, resiilting- in the material containing- but a 

 small amount of nitrogen witli a somewhat high content of 

 l)hosphoric oxide. 



It is probable that the above facts accoimt for smdi a 

 variation in tlie comi)osition of bat guano. 



J)('fl n/tion of lidf (rudno ond (tiki no Phosjilidte . — Bat 

 g'uano, as defined in the Reg-ulations of the Fertilisers 

 Ordinance, must contain at least 2A i)er cent, of nitrog-en 

 and 8 per cent, of jiitiogen and ])hos])horic oxide takeii 

 tog'ether. (irmino from Avliich all, or ])ractically all, the 

 nitrogen has disappeared shall not be sold as " guano," but 

 may be sold as " ])hos])hatic g'uano " or " guano ])li(is])hate." 



Bat guano may be classified as follows : — 



Zvitrog-enous bat g'uano. 



Phosphatic bat gintno or bat g'uano phosphate. 



Inferior bat guano. These are so poor in plant food 

 tliat they are of no commercial value, except on 

 the farm on which the deposit occurs. 



.\/fro(jenoiis Ihif (junnox. — These occur in a dry cave, and 

 contain all the plant foods — namely, nitrog-en, phosphoric 

 oxide and j^otash. Tln^ nitrog-en ccnitent of bat g'uano is of 

 a complex nature, as sucli nitrogen may exist in several 

 forms— (a) nitric, (b) ammoniacal and (c) organic. All these 

 forms are of different availability to plant growth. Plants 

 during' their yiowlh can make immediate irse of the nitric 



