THE USE OF MANURES 161 



cent.), but these, while costing less, are 

 distinctly less effective. 



All true guanos consist of excreta of sea- 

 birds. If the deposits are comparatively 

 fresh the nitrogen is high and the phosphate 

 low in quantity, but, in both cases, high in 

 quality. But the deposits may have lain 

 so long that much of the nitrogen has been 

 washed out, and what remains is com- 

 paratively inactive. With advancing decom- 

 position the phosphates increase in quantity, 

 but become less soluble, so much so, indeed, 

 as to be of little service till dissolved by 

 sulphuric acid, as in the manufacture of 

 superphosphate. 



CHAPTER VII 



THE EFFECTIVE USE OF ARTIFICIAL 

 MANURES 



IN connection with the use of artificial 

 manures generally, the following rules for 

 guidance should be observed. Attention 

 should be given to equal distribution of the 

 dressings, that is to say, the manures should 

 be evenly scattered over the land, and all 



