665 



Soils have the power of absorbing moisture from the air when 

 not expired to a hot sun, as at night time. This is a matter of the 

 highest importance in a hot climate, and the value of a soil is 

 greatly dependent on its power of absorbing and retaining moisture. 

 The more power it has of absorbing and retaining water, the more 

 hygroscopic will be the soil. Peat will absorb in one night one 

 twelfth of its weight in moisture, clay one-thirtieth of its weight, 

 while sand absorbs none, or, at most, a mere trace. It will thus be 

 seen that the absorbing, retentive, and hygroscopic powers of a 

 soil are directly dependent on the amount of organic matter or clay 

 that enters into its composition, and that the power can be increased 

 by the judicious addition of clay and organic matter to a sandy soil. 

 In a hot climate, such as we have in this colony, these various 

 powers of a soil necessary to their profitable cultivation should be 

 maintained at their best and improved as far as possible where they 

 are deiicient. The physical properties of a soil are just as impor- 

 tant as the chemical properties for keeping a soil in a fertile state. 



\Ve have seen that clayey and peaty soils contract when they 

 dry, and do not allow of the passage of oxygen and other gases 

 necessary for the plant growth. In the wet state they are so satur- 

 ated with stagnant water that oxygen cannot enter them, hence the 

 great necessity for drainage in these soils, which also prevents 

 sourness of the land, and enables them to absorb oxygen, carbonic 

 acid and ammonia in the form of gases. 



THE ABSORBTIOX OF GASES BY SOILS. 



Soils have the power of absorbing gases from the air, both 

 direct and from rain, which takes up oxygen, carbonic acid and 

 ammonia in its passage through the air to the earth. The soil also 

 receives carbonic acid from the decomposition of organic matter in 

 the earth, and in larger proportions than from the atmosphere. 

 The atmosphere H pr.ncipally composed of oxygen and nitrogen, 

 both of which gases aie absorbed by the soil, more especially 

 oxygen, for which it makes a greater demand than for nitrogen. 

 To enable the soil to receive sufficient of these gases it is necessary 

 that it should be open so as to allow of the free access of air ; this 

 is accomplished by tillage and drainage. It is a well known fact, 

 first proven by de Sansaure, that plants absorb oxygen directly 

 through their roots. The amount any plant absorbs varies at 

 different periods of its growth, and if not supplied freely at that 

 time the growth of the plant is delayed or stopped altogether. 



When seeds are germinating they require a good supply of 

 oxygen to enable them to sprout vigorously, and the young plants 

 require a plentiful supply, as they have not the strength or roots to 

 stretch out in search of supplies at a distance. Hence the great 

 necessity of a good seed bed, and not burying the seed too deep 

 in the soil. The soil absorbs nitrogen from the atmosphere, 



