INTRODUCTION. xiii 



functions, and may be of value not merely because 

 they supply to the soil nitrogen, phosphoric acid, or 

 potash, but also because they exercise some influence 

 on the soil's mechanical properties, or it may be, in 

 preparing for the plants' use inert fertilising substances. 

 The functions of a manure, therefore, may be very 

 varied, and no manure exemplifies this to a greater 

 extent than farmyard manure. 



