258 ARTIFICIAL MANURES [chap. 



by far the most important. These guanos consist of 

 the excrements of the sea-birds which frequent these 

 islands in enormous numbers during the breeding 

 season. Owing to the absence of rain, the material 

 accumulates from year to year with very little change, and 

 can be excavated and readily reduced to a fine powder. 

 It, however, undergoes some slow process of decay and 

 washing, so that while the recent deposits contain as 

 much as 15 per cent, of nitrogen and only about 20 per 

 cent, of phosphates, in the oldest deposits the nitrogen 

 is reduced to less than 3 per cent, while the phosphates 

 have risen to nearly 60 per cent. It is thus very 

 important to purchase a guano according to its analysis, 

 and not by its name alone. In any case these fertilisers 

 will be found to be dearer than the same amount of 

 nitrogen and phosphoric acid in other forms, the extra 

 price representing the farmer's long experience of their 

 kindly action upon his crops. The richer guanos, con- 

 taining 6 per cent, of nitrogen and upwards, are 

 extremely active fertilisers, the nitrogen being in forms 

 which readily get converted into ammonia, and the 

 phosphates being comparatively soluble in water. They 

 are also very safe, well-balanced manures, containing 

 nitrogen and phosphoric acid in much the same pro- 

 portions as are required by plants, and also a little 

 potash. Moreover, many different compounds of 

 nitrogen are present which differ in the rate at which 

 they will decay, so that the plant is fed continuously, and 

 suffers from no excess of available nitrogen in the soil at 

 any time. Such a fertiliser leads to a steady, equable 

 growth, which is generally attended by superior quality 

 in the product. Thus the Peruvian guanos become 

 excellent fertilisers for crops where the quality is of 

 importance, and where it is not necessary to cut down 

 the expenditure on fertilisers to the lowest limit. 



