24 



AERATION AND AIR-CONTENT. 



series gained more than 50 per cent in dry weight over the plants in 

 the non-aerated one. 



Harrison and Aiyer (1914 : 93) have determined the beneficial 

 effect of drainage on the growth of rice in pots. The results are 

 shown in table 4. 



TABLE 4. 



When the drainage was made complete, so that air could enter the 

 soil, there was likewise a definite increase in the production, which 

 reached a maximum between 1 and 2 days' aeration. This was less 

 marked than in simple drainage, however, owing to the greater 

 amount of oxygen in the soil-water as a result of the activity of algae. 



Hole and Singh (1914), in studying the relation of sal (Shorea 

 robusta) to air-content, found that germination was best in the well- 

 aerated sandy soil and that it was 8 to 32 per cent less in loam and 

 leaf -mold. As to the seedlings, 12 per cent died in watered loam and 

 26 per cent in watered leaf-mold to none in watered sand. In porous 

 pots, germination was best in sand, 8 per cent less in loam, and 28 

 per cent less in leaf-mold. In the case of the last two, germination 

 was 50 per cent less in painted than in porous pots. The plants in 

 the painted sand pots remained healthy throughout the rains, while 

 24 per cent died in the loam and 40 per cent in the leaf-mold. When 

 the pore-space of a soil is reduced by mechanical pressure, 25 per 

 cent more plants may die in it during the rains than in the normal 

 soil, while the survivors have an abnormal root-system confined to 

 the upper, better-aerated layer. When seedlings are grown in 

 glazed pots, some of which are corked, they become unhealthy in 

 the open in about 10 days and eventually die, while in uncorked pots 

 they remain healthy. Similar consequences ensue when the drain- 

 age holes are not corked, but the surface of the soil is covered with a 

 thick layer of sal leaves. 



Cannon (1915 : 64) aerated roots of Opuntia at 32 C. for alternate 

 periods of 2 hours and found that the average rate of growth was 1.59 

 mm. for the aerated period and 1.25 mm. for the unaerated one. 

 The increase due to aeration thus amounted to more than 25 per 

 cent. 



