131 



CHAPTER III. 



ACTION OF SOIL OX FOOD OF PLANTS IN MANURE. 



Manures : meaning of tlie term ; tlieir action as food of plants and means 

 for improving the soil — Eftect on soils witli dillerent powers of ab- 

 80i"ption — Each soil possesses a definite power of absorption ; the dis- 

 ti-ibution of the food of plants in the soil is inversely to the power of 

 absorption; means of counteracting the absorptive power — Absorption 

 number, notion of; comparison of in different fields; its importance in 

 husbandry — Soil saturated with food of plants; its comportment wnth 

 water — Quantity of food to saturate a soil — A saturated soil not re- 

 quired for the growth of plants — Manuring may be compared to the 

 application of earth satm-ated with food — Importance of the uniform 

 distribution of food in manures ; fresh and rotted stall manure ; compost ; 

 impoitance of powdered turf for the preparation of manure — Quantity 

 of food in unmanured fields and their powers of production ; increase of 

 the latter apparently out of proportion to the manure added ; experiments 

 on this point ; explanation ; composition of the soil and its absoi-ptive 

 power compared with the requirements of the plants to be cultivated on 

 it ; surface and subsoil plants, the tillage and manuring respectively 

 required by each — Clover sickness; experiments of Gilbert and Lawes; 

 theii' conclusions ; value of them. 



THE term ' manure ' is commonly used to designate all 

 matters whicli, 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, hke common salt, nitrate of 

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

 mechanical operations of tillage, so that they frequently 

 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 



K 2 



