318 



On Guano. 



aware of very beneficial results having been obtained during the 

 past season from the application of sal ammoniac in admixture 

 with other substances, without the presence of chalk. 



I consider the above mixture as likely not only to be equally 

 efficient with 4 cwt. of guano, costing at present bl., but ulti- 

 mately it may be more so ; and this chiefly because in specifying 

 the ingredients no account has been taken of the animal matter 

 present in the bones, though the quantity of gelatine they contain 

 is itself sufficient during its slow decay to yield about 30 lbs. of 

 ammonia to the soil. I have not taken this into account, because 

 the special and immediate action of guano seems to depend upon 

 its containing, like farm-yard manure, ammonia ready formed, and 

 thus prepared to act without delay on the plant to which it is 

 applied. That growth which the ammonia of the sal ammoniac 

 in our mixture is fitted to hasten and provoke, the ammonia which 

 is afterwards slowly evolved from the decaying animal matter will 

 carry forward and help on to maturity. The few pounds of 

 potash in the mixture have been added, not because this substance 

 is always present in the guano, but because it is known that nearly 

 all plants require a certain small quantity of this alkali for the 

 perfect development of their several parts. Another advantage 

 which will be possessed by the artificial mixture will be, that its 

 constitution will be constant, and may always be calculated upon. 



From these theoretical considerations, therefore, we should say 

 that until its virtues are proved to be greater^ beyond dispute, 

 than those of the above or similar mixtures, the practical farmer 

 ought not to purchase guano at a higher price than 205. per cwt., 

 a price which in the opinion of Mr. Pusey the farmer may pro- 

 bably afford to pay — which according to Mr. Winterfeldt would 

 more than remunerate the importer—and below which, according 

 to the chemist, an artificial guano of equal efficacy may be prepared 

 in England, and from the super abundant produce of cur own 

 mamfadories. 



§ 8. Of Comparative Experiments with Guano and other Manures. 



But the absolute value of guano itself, as well as its rela- 

 tive value compared with other manures, can only be placed 

 beyond dispute by actual and comparative trials of its efficacy in 

 different soils and upon different crops. To be really useful and 

 satisfactory these trials must be made according to some well- 

 digested method, and the comparison must be made with known 

 weights of other substances^ the action and money value of which 

 are known, and which from their constitution may be supposed to 

 act on vegetation in a similar way. As I have elsewhere en- 

 deavoured to draw the attention of practical men to the importance 



