60 THE CHEMISTRY OF THE FARM 



oxidation of the organic matter previously accumulated 

 commences, and the amount of drainage and the losses 

 by drainage are much increased. The vegetable and 

 animal produce of the land are also now consumed off 

 the soil which has reared them. Provision must con- 

 sequently be made, sooner or later, to return to the 

 land a part at least of the plant food removed from it 



its fertility is to be maintained. Hence the neces- 

 sity for manuring. 



A nearly complete return to the land would be 

 accomplished by manuring it with the excrements of 

 he men and animals consuming the crops. This is 

 partially done by the application of farmyard manure; 

 but the congregation of men in cities, and the difficulty 

 of employing sewage with profit, prevent this plan 

 being thoroughly carried out. The farmer is thus often 

 obliged to purchase manures for the land in exchange 

 for the crops and stock sold off it. 



On naturally poor soils it may be necessary to make 

 a complete return of all the elements of plant food 

 removed by the crops ; but in most soils there is an 

 abundance of some one or more of these elements, and 

 a partial manuring will consequently suffice. With 

 high farming the contributions to the soil may be 

 in excess of the exports, and the land consequently 

 increase in fertility. The nature of the exhaustion 

 resulting from the growth of particular crops, and the 

 economic application of manures to meet their special 

 requirements, will be considered in Chapter IV. ; the 

 losses during a rotation of crops in Chapter V. ; the 

 losses by the sale of animal products in Chapter VI. 



rarmyard Manure consists of the liquid and solid 



