20 BULLETIN 169, U. S. DEPARTMENT OF AGRICULTURE. 



the time of germination is when acid applied to the beds will do the 

 most damage to pine seedlings. The longer the period before or after 

 ger min ation takes place that the acid is applied the less danger there 

 is of acid injury. The free acid in the soil solution would normally 

 be decreased by diffusion or leaching downward into the subsoil, by 

 adsorption or solid solution by the soil, and by chemical interaction 

 with other constituents of the soil or soil solution. No attempt has 

 been made to determine the relative importance of these different 

 processes in the removal of the acid from the solution. It has seemed 

 rather surprising that even with applications of acid as small as 0.25 

 ounce per square foot enough acid remains free in the surface soil 

 three weeks after application to kill the tips of jack-pine roots and 

 prevent the growth of most dicotyledonous weed species for 1-| months. 

 In soil containing large quantities of carbonates there could be no such 

 length of persistence of free acid. 



The amount of injury occurring in plats treated at different lengths 

 of time before germination and the comparative lack of relationship 

 between the amount of acid used and the extent of injury in cases 

 where more than 15 days elapse between treatment and germination 

 indicate that the rate of dissipation of the free acid in the soil solution 

 decreases rapidly as the concentration decreases. Very small 

 amounts of acid have proved extremely injurious to root tips in the 

 soil at the time of application. While they lose this extremely toxic 

 character in a very few days after application, the final reduction to 

 a point where no injury occurs requires a relatively long time. The 

 apparent relative stability of very low concentrations of acid in the 

 soil solution is in agreement with the general course of removal of a 

 solute either by diffusion or chemical reaction. 



ADDITION OF NEUTRALIZING AGENTS AFTER THE APPLICATION OF THE ACTD. 



In different experimental series, plats treated with sulphuric acid 

 before sowing were later treated with neutralizing agents to prevent 

 acid injury. This procedure greatly decreased the effectiveness of 

 the acid treatment against the damping-off parasites on whose 

 account the work was being conducted, and so it was not exhaustively 

 tested. In no case was lime applied to the extent of equivalent 

 weights of the acid used. 



The indications are that injury to pines may be prevented by small 

 amounts of lime put on the beds a few days after the application of 

 the acid. The results of the treatments are given in Table V. 



