CULTIVATION. 87 



financial profit. The better the tillage the larger is the 

 crop obtained and hence the greater is the amount of plant 

 food which the crop has been able to take. This increased 

 vigour of the plant is the result of the effect of tillage on 

 the chemical, physical and biological properties of the soil. 

 The tillage is only satisfactory when the soil is in a loose, 

 friable condition ; that is, when the tilth is fine. The soil 

 tends to form itself into a solid mass which gradually be- 

 comes more tightly packed, and offers ever more resistance 

 to the spread of the plant roots and the entrance and action 

 of the weathering agents. Irrigation, by carrying down the 

 finer soil particles and packing them into the air spaces, 

 decreases the porosity and permeability of the soil while 

 increasing its tenacity. Naturally, fine clay soils pack 

 most closely and therefore require most cultivation. 



The physical effect of tillage is that the soil is thrown 

 open and left loose, allowing a free passage into it of 

 water and air. The soil is pulverised, large pieces are 

 broken up, and a greater surface is presented to the action 

 of the weathering agents. The finely pulverised soil 

 forms a better medium for germinating seeds, as the 

 seed and soil come into closer contact and better germi- 

 nation is got. Further, in fine tilth, the young seedlings, 

 being covered with a loose and equal layer of soil, are 

 better able to develop their roots, and to send their stems 

 into the atmosphere. The loose soil offers less resistance 

 to the spread of plant roots and as the quantity of water 

 and air is regulated, the plant root becomes larger and 

 healthier. It can readily be understood that plants with 

 large roots draw their nourishment from a greater volume 



