CHAPTER X 



MANURES SUPPLYING ORGANIC MATTER: 

 FARMYARD MANURE 



Organic matter is a general expression used to denote 

 substances of animal or vegetable origin in contradis- 

 tinction to the nitrates, phosphates and potassium salts 

 which are termed inorganic. It contains carbon, hydro- 

 gen and oxygen and is combustible : this property is used 

 in practice for distinguishing it from the inorganic 

 matter of soils or fertilisers which is usually non-com- 

 bustible. 



Organic matter differs in twoimportant directions from 

 the mineral substances studied in the preceding chapters. 

 Nitrates, phosphates, and potassium salts are directly 

 assimilated by plants; organic matter apparently is 

 not, and it derives no fertilising value from its three 

 characteristic components but only from any nitrogen, 

 phosphorus or potassium it may contain. Before these 

 elements can be utilised by the plant, decomposition 

 must take place in the soil; this is effected by moulds 

 and bacteria, and gives rise to ammonia, carbon dioxide 

 and certain complex residues grouped together as 

 humus. The fertilising value of the organic matter de- 

 pends very much on the rate at which this decomposition 

 proceeds, which in turn is determined by the bacterial 

 efficiency of the soil and by the nature of the substance. 

 Protein and the simpler compounds such as urea are 

 rapidly decomposed to form ammonia in the soil, but 

 the more complex substances which occur in straw, 



