CONTENTS. 15 



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

 ently 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 manuring respectively required by each Clover 

 sickness ; experiments of Gilbert and Lawes ; their conclusions ; value of 

 them, ... 134 



CHAPTER IV. 



FARM-YARD MANURE. 



The fertility of a soil depends upon the sum of available food, the continuance of 

 the fertility upon the total amount of all food in it Chemical and agricultural 

 exhaustion of the soil Exhaustion of the soil by cultivation, laws regulating 

 its progression ; effect of the transformation in the soil of the chemically fixed 

 into physically fixed elements of food ; effect on the progress of exhaustion by 

 partial restoration of the withdrawn food of plants Progress of the exhaustion 

 by different cultivated plants Cultivation of cereals, consequence of removing 

 the grain and leaving the straw in the soil ; intervening clover and potato 

 crops , effect of leaving in the ground the whole or a portion of these crops ; 

 division of soils ; productive power of wheat fields increased by accumulating 

 in them the materials derived from clover and potato fields ; cultivation of 

 fodder plants ; their food partly derived from the subsoil ; addition of these in- 

 creases the productive power of the surface soil Natural connection between 

 the cultivation of cereals and fodder plants, the influence on the fertility of 

 land Exhaustion of the soil rc a moved by the restoration of the withdrawn 

 mineral constituents ; the excrement of men and animals contains these ; their 

 restoration depends upon the agriculturist, . . . . .164 



CHAPTER V. 



THE SYSTEM OP FARM-YARD MANURING. 



Questions to be solved Experiments of Renning, their significance Produce of 

 unmanured fields Influence of preceding crops, of the situation, and climatic 

 conditions, on the produce Each field possesses its own power of production 

 Large crops, their dependence and continuation Closeness of the food of 

 plants, what is meant thereby The closeness of the particles of food in the 

 soil is in proportion to the produce Produce of corn and straw influenced by 

 the relations of the assimilated food and by the conditions of growth ; action 

 of food supplied in manures Potatoes, oats, and clover crops of the Saxon 

 fields ; conclusions drawn from them as to the condition of the fields Produce 

 of these fields from farm-yard manure ; the increase of produce cannot be cal- 

 culated from the amount of manure used Restoration of the power of produc- 

 tion of exhausted fields by the increase of the necessary elements of food pres- 

 ent in the soil in minimum amount ; advantageous use of farm-yard manure 

 in this respect ; explanation of the result Action of manure as compared with 

 quantity used : experiments Rational system of cultivation Depth to which 

 the food of plants penetrates is dependent on the power of absorption of the 



