THE NATURE OF SOIL 45 



plant food in most fertilisers applied to soils would 

 be quickly leached or washed away, if these chem- 

 ical changes did not occur and hold it until the 

 roots of plants can use it. Plants feed, not upon the 

 materials that we apply to the soil ashes, bones, 

 phosphates, guano, and the like but upon the 

 chemical compounds formed in the soil by them. 



These and other chemical changes that all fer- 

 tilisers pass through before they are absorbed by 

 the roots of the plants illustrate what takes place 

 with each and every constituent of the soil, whether 

 it is essential to the growth of the plant or not. The 

 soil is a great chemical laboratory. Numberless 

 reactions, or new adjustments of the partnerships 

 between the elements, occur every hour. No 

 chemist holds the beaker or fires the great retort; 

 the changes take place in obedience to natural 

 laws, quietly and methodically, yet with results so 

 far reaching that we can hardly grasp their signifi- 

 cance. It is the business of the chemist and the 

 bacteriologist to explore this laboratory and report 

 how its chemical changes are effected by the dif- 

 ferent methods of handling the soil. It is the 

 business of the farmer to keep the soil laboratory 

 in excellent working order, by a wise and varied 

 husbandry; and especially by giving careful atten- 

 tion to those principles of good farming that we 

 already know make it run smoothly thorough 

 tillage, excellent drainage, and a rotation of crops. 



