EFFECT OF DISSOLV ED SALTS ON WATER MOVEMENT 63 



Measurement of D/Dq for the diffusion of hydrogen through the dry 

 stones using the method of Currie (i960) gave 



Portland D/Do= 0-0430 

 Greenbrae -D/Dq = 0-0664 



Akhough the almost exact agreement is probably fortuitous, it suggests 

 that the analysis is correct, and the assumptions in it are acceptable. One of 

 these, between eq. 8 and eq. 9, takes ql/Ds as small. Its value for Portland 

 stone is 0-045, and the assumption is vaHd. 



lOr 



l/K' 



PORTLAND/" 



X 10'° sec /cm 



GREENBRAE 



j_ 



0.2 0.4 0.6 



NaCI CONCENTRATION mo 



0.8 



Fig. 2. The effect of dissolved salts on water movement. 



CONCLUSION 

 In soil in which there is both a matric potential gradient and an osmotic 

 potential gradient the bulk movement of water is controlled only by the 

 former even though the latter may add greatly to the total potential 

 gradient, or even impose an opposing gradient, which will happen when 

 fertihsers are drilled in bands alongside the plants. There seems to be no 

 serious risk that the very strong osmotic gradient set up by the fertiHser 

 will successfully compete with the plant roots in drawing water out of the 

 region between them. Water vapour will, it is true, move towards the 



