On Guano. 



313 



decompose and disappear in great measure from the soil in one 

 or two seasons, but the bone-earth (the phosphate of lime) re- 

 mains long in the land, is — in small quantity only, and therefore 

 slowly — withdrawn from the soil by the crops and by other natural 

 agencies, and thus may continue to exercise a beneficial influence 

 on the fertility of the field to which it is applied for a long period 

 of time. 



The same remarks apply to guano. On an average, 150 lbs. 

 of guano may contain as much bone-earth as 100 lbs. of bones;* 

 and in the same proportion will its action on the land, compared 

 with that of bones, be permanent — in so far as this ingredient is 

 concerned. 



This fact is of great practical importance. Nitrate of soda, so 

 much used of late and so deserving of more extensive trial, may be 

 washed out of the soil where the earthy part of the guano would 

 remain : it may cease to exert a marked influence after a single 

 crop, where it is scarcely possible that the phosphates of the 

 guano should cease to act ; and it may fail to bring to maturity 

 crops of corn or to fill the ripened ear, when the guano would 

 supply to the grain, among other substances, the earthy phosphates 

 also, which the seed contains as a necessary constituent. 



While then the ammonia of the guano promotes the early 

 growth, its phosphates supply to the ripening plant the materials 

 which are indispensable to its perfect development. The nitrates 

 also, like ammonia, aid in a remarkable degree the growth of the 

 plant in its earlier stages ; but, except the potash or soda which 

 the nitrate may contain, it can supply to the maturing vege- 

 table none of the inorganic substances it is known to require. 

 Unless these are present in sufficient quantity in the soil, the 

 healthy appearance of the young plant, whether imparted to it by the 

 agency of ammonia or by that of nitrate of soda, cannot be safely 

 trusted to as an index of the weight of corn we are to reap, when 

 the time of harvest comes. 



4. The presence of common salt in the guano need not sur- 

 prise us. It is no doubt derived from the sea, partly through the 

 medium of the birds themselves, and partly from the evaporation 

 of the salt-spray continually driven upon the coasts by the winds. 

 It is variable in quantity, as we should expect from a knowledge 

 of its origin. The beneficial effect of common salt when applied 

 to the land has been frequently recognised in many localities and 

 upon many soils. It no doubt aids the other ingredients of the 

 guano in producing its full effect upon the living vegetable. 



The important influence of guano, therefore, on the vegetation 



* Four cwt. of guano as much as 7 bushels of bones, supposing the 

 guano to contain about 35 per cent, of phosphate of lime, which is less than 

 the mean of the specimens I examined. 



