NURSERY PRACTICE ON THE NATIONAL FORESTS. 81 



INCOMPLETE FERTILIZERS. 



WOOD ASHES. 



With the exception of nitrogen, which is lost during the process 

 of burning, wood ashes contain all the nourishing substances, pot- 

 ash, lime, phosphoric acid, magnesia, and sulphuric acid, in a form 

 capable of absorption. Wood ashes may accordingly be added to the 

 list of fertilizers for general use. The quantity of these elements, 

 particularly phosphoric acid and potash, contained in the ashes 

 varies with the species, the ash of hardwoods being much richer in 

 such material than that of conifers. In sandy soil care must be 

 taken in using wood ashes, because such soil is not capable of much 

 absorption. The use of such a strong fertilizer has an unfavorable 

 effect, because it furnishes the roots with too much carbonate of 

 potash, which acts as an alkali ; on the other hand, its use on clayey 

 humic soil is very favorable. Pure wood ashes, however, are seldom 

 used but are generally mixed with compost; their use deserves all 

 the more consideration, as they can usually be obtained at little 

 expense by burning the brush around the nursery or by utilizing 

 the wood ashes from the stoves of the nursery buildings. 



NITROGEN FERTILIZERS. 



Nitrate of soda NaN0 3 (Chili saltpeter) contains 15 or 16 per 

 cent of nitrogen, is easily dissolved by water, and quickly distributed. 

 It has a quick and decisive effect, but the portion not absorbed at 

 once by the plants quickly sinks to the subsoil and may be lost. Its 

 best use is for intermediate fertilizing — that is, the fertilization of 

 beds in which after the growing season has started the plants appear 

 unhealthy and the cause is apparently due to lack of nitrogen. 



A somewhat better commercial nitrogen fertilizer for forest tree 

 nurseries is ammonium sulphate (NHJ 2 S0 4 , obtained from the 

 refuse in gas manufactories where the ammonia produced is fixed by 

 sulphuric acid ; the white salts contain about 21 per cent of nitrogen, 

 which is only effective after being changed into nitrates. A simul- 

 taneous fertilization with lime or carbonate of lime should be 

 avoided, as in such a case by decomposition of the salts the ammonia 

 becomes ineffective and evaporates. 



Blood powder or blood guano, made from the blood of slaughtered 

 animals mixed with powdered lime, contains from 10 to 12 per cent 

 of nitrogen and from 1 to 2 per cent of phosphoric acid. Horn pow- 

 der made from the refuse of horns, hoofs, and hair, ground and 

 63186°— Bull. 479—17 6 



