66 4 



long duration, it is necessary that the soil should be able to retain 

 a sufficiency of moisture to enable the plant to take up an adequate 

 supply of food in order to attain maturity. It has been shown 

 that silicious sand has the lowest power of absorbtion, and 

 consequently the lowest power of retention, and that humus has the 

 highest power of retention. Hence the great benefit of green 

 manuring a sandy soil, which means the addition of a certain 

 amount of organic matter, or humus. It is also evident that drain- 

 age is of the utmost necessity in clay and peaty soils. Too much 

 moisture in a soil is just as bad, if not worse, than too little. 

 Maerker gives the effect of different proportions of water in the soil 

 upon the growth of summer rape as follows : 



It will be seen that from 40 to 80 per cent, is the amount of 

 water a soil can hold in the best proportions. When less or more 

 the results are not so favorable, as it affects the plant growth in 

 every part. When too much water is in the soil it becomes cold, 

 and a free circulation of air, absolutely necessary to healthy growth, 

 is prevented. A dry soil develops the plant quicker than a damp 

 one. 



The amount of evaporation that takes place in any soil is 

 gre iter when under cultivation than when bare. It also depends on 

 the openness of the soil. An open soil does not lose water so 

 quickly as a close compact one, owing to the capillary power being 



The a Idition of clay to sandy soils greatly increases their 

 retentive powers. On the other hand, clayey and peaty soils are 

 more liable to contract when dried than sand or limestone. 

 The result of this shrinking of clay and peat is to compress the 

 roots of the plants and form such a hard compact mass that air is 

 not allowed to enter into the soil. Sand does not contract on 

 drying. When sand is mixed with clay it keeps it in a porous 

 state, so that the air can always pass through it. 



