Application and Persistence 197 



inhibitors (Audus, 1951) and consequently the protective effect ap- 

 pears to be due to the prevention of auxin from outside the root zone 

 entering into contact with the root. 



The effectiveness of activated (arbon as an ads(M|)ti\e agent to 

 remove residues from spray ecjuipment has been demonstrated by 

 Lucas and Hamner (1947). 



Leaching. The second major factor in the persistence of auxins 

 in soils is that of leaching. Obviously the ease with which a material 

 can be leached from a soil will be strongly influenced by adsorption, 

 as we have discussed in the previous paragraphs, and the adsorptive 

 properties will vary with soil type. Besides adsorption, the solubility 

 of the auxin will play a role here. Early observations indicated that 

 liming or an excessively calcareous condition would retard leaching 

 of auxins (Kries, 1946; Muzik et al, 1951). This would presumably be 

 accounted for on the basis of the formation of auxin salts such as the 

 calcium salt which are relatively insoluble. Other reports have failed 

 in several instances to confirm that liming or calcareous conditions 

 retarded leaching (Hanks, 1946; Akamine, 1951), but the experiment- 

 ers have seldom distinguished between adsorption and leaching and. 



IS Inches 



AMOUNT OF LEACHING WATER 



Fig. 82. The relative rates of leaching of 2,4-D from the surfaces of three dif- 

 ferent soils by various amounts of leaching water. The amount of 2,4-D remaining 

 was quantitatively estimated by the inhibition of grabgrass seedlings (Ogle, 1953). 



