58 PLANT PRODUCTS 



while carpets of pine needles form a useful mulch on the 

 surface, but decay only very slowly. 



Peat is also a material which can be used for fertilizing 

 purposes on light sandy soils, or on heavy clays. It improves 

 the water supply and aeration of the soil. Much attention 

 has been directed to the attempt to ferment peat into some- 

 thing more immediately active. This very old idea has been 

 revived recently, in the effort to give a carefully directed 

 bacterial fermentation in place of a more haphazard decom- 

 position. Very valuable reports on humogen have been given 

 by Voelcker and Russell (see Bibliography). Whenever such 

 materials as peat, having a very high capacity for absorbing 

 water, are added in large quantities to a soil, they are perfectly 

 certain to produce a beneficial result, but the expense and 

 labour involved will often detract from their value. 



Conclusion. The very varied by-products of the in- 

 dustries which are capable of being used as fertilizers have 

 been discussed above in moderate detail. Consultation with 

 the various books referred to in the Bibliography will give 

 many further details. Unintelligent use of fertilizers can 

 easily do more harm than good, and a knowledge of the proper 

 fertilizers requires not merely a knowledge of the fertilizers 

 themselves, but also of the types of soil to which they are to 

 be applied, the crops proposed to be grown, and the conditions 

 under which the cultivation of these crops is undertaken. 



REFERENCES TO SECTION IV 



Collins, " The Valuation of Manures," The Journ. of the Land Agents 

 Society, Sept., 1908, p. 452. 



Richards, " The Fixation of Nitrogen in Faeces," Journ. Agric. Science, 

 8, p. 299. 



Russell and Golding, " Investigations on ' Sickness ' in Soil," Journ. 

 Agric. Science, 5, 27. 



Fowler and Clifford, "Notes on the Composition of Sundry Residual 

 Products from Sewage," Journ. Soc. Chem. Ind., 1914, p. 815. 



Rideal, " Sewage and the Bacterial Purification of Sewage," p. 330. 

 (The Sanitary Publishing Co.) 



Dibdin, "The Purification of Sewage and Water," p. 108. (The 

 Sanitary Publishing Co.) 



Rideal,- " Disinfection and Disinfectants," p. 238. (Griffin.) 



Weiss, " Directions for Preparing Manure from Peat," Journ. Board of 

 Agric., 1916-17, p. 481. 



Russell, " Report on Humogen," Journ. Board of Agric., 1917-18, p. n. 



