52 



SOIL CONDITIONS AND PLANT GROWTH 



Livingstone and E. E. Free (ly^c) grew plants in soil so 

 sealed that its atmosphere could be controlled. Different 

 plants varied in their susceptibility to the exclusion of 

 oxygen ; Coleus blumei and Heliotropium peruvianum were 

 the most sensitive, the intake of water in their roots ceasing 

 within 12 to 24 hours owing to death of the roots and the 

 entire plants ultimately died when oxygen was replaced by 

 nitrogen. Salix nigra, on the other hand, successfully en- 

 dured the exclusion of oxygen. 



Application of these general results to field conditions 

 have been made in India by A. and G. L. C. Howard (139), 

 who have shown that increased soil aeration resulting from 

 lessened irrigation or addition of potsherds to the soil leads 

 to increased plant growth. Some of their results are given in 

 Table XIII. :— 



Table XIII. — The Effect of Diluting the Pusa Soil with Potsherds 

 OR Sand. A. and G. L. C. Howard (139). 



Effect of Reducing Irrigation and thereby Increasing Air Supply. 



Wheat. 



Hall, Brenchley, and Underwood {i2id) found considerable 

 differences in the amount of growth of lupins in sand and 

 kaolin on the one hand, where ample aeration was possible, 

 and fine sand, silt, or water culture on the other where there 

 was much less aeration. Their results are : — 



