675 



Mixing of soils, as I have already said, greatly improves them 

 both physically and chemically. The addition of sand to a heavy 

 clay makes it more pervious and admits of a freer circulation of 

 water and air through it. \Yater is one of the most necessary 

 elements of the plant food ; at least it is required in larger propor- 

 tions than any of the others. Water to be of any use to the plant 

 must be a moving water and well Derated. 



If the subsoil is a heavy clay the water gets stagnant in it, and 

 does not allow a free passage of atmospheric air. The organic 

 matter decomposes very slowly, forming poisonous organic com- 

 pounds, which are retained in the deep soil. The roots of the 

 crop passing down into the deep soil in search of food come in 

 contact with these poisonous substances and die off. What was, 

 up to that time, a strong healthy crop, sickens and droops, till it 

 either dies away or remains of a stunted growth. Even if the roots 

 do not pass down to these poisonous substances, as soon as the 

 surface water evaporates, there will be an upward movement of 

 water which will affect the crop more or less according to the 

 amount of these deleterious substances it carries with it from below. 

 Hence the great necessity of deep drains on heavy clay and peaty 

 soils. The drainage of the soils increases their fertility in several 

 ways. Wet soils are cold, and lack a genial warmth. After a long 

 drought they contract and crush the roots, and do not allow the 

 free passage of the roots through them in search of food. When 

 the quantity of water in a soil is too great, the food for the 

 nourishment of the crops will be in a very diluted condition, 

 and the plant will require to absorb a very much larger quantity 

 ot water than is necessary for its proper growth. The pre- 

 sence of so much water in the plant will necessitate a greater 

 evaporation from the leaves, thus producing a lower temperature in 

 the plant than is natural to it, thereby delaying the chemical 

 changes that take place during the plant's growth. The water 

 being carried into the drain will take with it the injurious com- 

 pounds out of the reach of the roots of the plant. It will cause 

 a downward flow of water, which will carry with it a good supply 

 of fresh air into the soil, which is necessary to its fertility. The 

 free passage of air into the soil causes a rapid oxidation of the 

 vegetable matter, converting it into plant food, carbonic acid, and 

 prevents the formation of noxious acid compounds. The decom- 

 position of the mineral matter in the soil tit for plant food is then 

 more active. The formation of hardpans is greatly prevented by 

 keeping the subsoil open. Soluble plant food is carried down to 

 the roots from the surface. 



Tillage improves the soil by dividing the particles of the soil 

 more minutely, rendering it more open and light, and allowing an 

 easier access of air and a freer passage for the roots in their search 

 for food. By turning over the soil more of the insoluble particles 

 are exposed to the weathering agents for the preparation of the 



