TILLAGE AND DEAINING 47 



crops have very different powers of attacking these 

 various forms of plant food. 



13. Tillage and Braining. — The operations of tillage 

 and draining serve in many important ways to make 

 the conditions of plant life more favourable, and to 

 increase the amount of plant food which is at the 

 disposal of a crop ; many of these have been already 

 noticed. 



By tillage, aided by frost, and by alternate drought 

 and rain, the surface soil is pulverised, and brought 

 into a loose, open condition. The fine tilth thus 

 obtained allows of a rapid extension of the delicate 

 root fibres, and favours a happy condition of soil 

 moisture. 



By the action of the plough the residues of crops, 

 weeds and manure are buried, and incorporated with 

 the soil. The deep tillage of heavy land allows rain 

 to penetrate it, and estabHshes the drainage of the 

 surface soil, and increases its temperature. A shallow 

 surface tillage preserves the moisture of the soil in 

 time of drought. By rolling a pulverised soil we 

 increase the moisture at the surface, and the depth 

 to which the soil is warmed by the sun. 



Another important result of tillage is that the soil 

 is thoughly exposed to the influence of the air. Soils 

 containing humus or clay will, under this condition, 

 absorb some ammonia from the atmosphere. The 

 oxidation of the nitrogenous organic matter present 

 in the soil will also be greatly facilitated, carbonic and 

 nitric acids being produced. The disintegration and 

 solution of particles of rock will take place from the 

 mechanical and chemical actions brought into play. 

 Of the chemical results brought about by tillage the 



