CHAPTEE III. 



ACTION OF SOIL ON FOOD OF PLANTS IN MANURE. 



Manures : meaning of the term ; their action as food of plants and means for im- 

 proving the soil Effect on soils with different powers of absorption Each soil 

 possesses a definite power of absorption ; the distribution of the food of plants 

 in the soil is inversely to the power of absorption ; means of counteracting the 

 absorptive power Absorption rumber, notion of; comparison of in different 

 fields , its importance in husbandry Soil saturated with food of plants ; its 

 comportment with water Quantity of food to saturate a soil A saturated 

 soil not required for the growth of plants Manuring may be compared to the 

 application of earth saturated with food Importance of the uniform distribu- 

 tion of food in manures ; fresh and rotted stall manure ; compost ; importance 

 of powdered turf for the preparation of manure Quantity of food in un- 

 manured fields and their powers of production ; increase of the latter appa- 

 rently out of proportion to the manure added ; experiments on this point ; 

 explanation ; composition of the soil and its absorptive power compared with 

 the requirements of the plants to be cultivated on it ; surface and subsoil 

 plants, the tillage and manurirg respectively required by each Clover sick- 

 ness ; experiments of Gilbert and Lawes ; their conclusions ; value of them. 



THE term ' manure' is commonly used to designate 

 all matters which, applied to a field, will increase 

 the amount of its future produce, or, when the land has 

 been exhausted by cultivation, will restore its capability 

 of yielding remunerative harvests. 



Manuring agents act partly in a direct manner as 

 elements of food, and partly, like common salt, nitrate 

 of soda, or salts of ammonia, by enhancing the effect of 

 the mechanical operations of tillage, so that they fre- 

 quently exert as favourable an influence as the actual 

 increase of the nutritive substances in the ground. 



Of the two last-named compounds, nitrate of soda 

 contains a nutritive substance in the nitric acid, and 

 salts of ammonia in the ammonia. Hence it is ex- 

 tremely difficult in individual cases to determine 

 whether their action is due to their nutritive constitu- 

 ents, or to the fact that they have brought about the 

 absorption of other nutritive substances. 



