18 CIRCULAR 862, U. S. DEPARTMENT OF AGRICULTURE 



DDT, inclusive, there was no significant reduction in growth. 

 In only 9 of the 27 separate tests of sensitive species on muck 

 did significant differences appear, and they occurred only at the 

 high levels of DDT. 



It should be pointed out that several tests were run on a second 

 lot of muck of unknown origin that contained a large amount 

 of silt and that had a pH of approximately 6.0. All DDT-sensi- 

 tive plants grown on this muck showed a somewhat greater 

 response to DDT than when grown on the New Jersey muck on 

 which most of the tests were run. Even at the 1,000-pound level 

 growth of sensitive crops on the unlimed New Jersey muck was 

 as good as on the average of the mineral soil controls. The 

 average of the two muck soils receiving 1,000 pounds of DDT 

 (table 2) showed little more relative reduction below the muck 

 controls than the 100-pound treatment on mineral soils showed 

 below the mineral soil controls. 



The five crops that are rated as less sensitive (according to theii 

 response on mineral soils) grew as well or better on the DDT- 

 treated muck as on the muck controls. The sweet corn appeared 

 to be benefited somewhat by the 1,000 pounds of DDT on the 

 muck, but the difference was not significant. This suggestion of 

 stimulation of sweet corn by DDT in the soil appeared also in 

 the field work to be described later. Although there are significant 

 increases in growth of sweet corn accompanying increasing 

 amounts of DDT above the control in the mineral soil, there are 

 no significant increases above the 25-pound treatment. 



Although the DDT on the plots of acid muck from New Jersey 

 showed no measurable effect on plant growth during the first two 

 series of tests, the soil was so highly acid that certain acid- 

 sensitive crops such as beets and spinach could not be grown 

 satisfactorily. Therefore, over a period of months dolomitic 

 limestone was added in successive moderate amounts, gradually 

 raising the pH of the muck from approximately 4.5 to 5.7. There 

 were a few indications that this rise in pH was accompanied b> 

 some increase in toxicity (or emergence of toxicity) of DDT at the 

 highest levels of treatment. The number of tests with the same 

 varieties on this soil both before and after liming was, however, 

 too small to give conclusive results on this point. . On the silty 

 muck soil having the higher original pH (6.0) several levels of 

 DDT appeared more toxic than on the other muck. It is not novv 

 possible to say to what extent pH might have affected these re- 

 sults and to what extent other, and unknown, factors affected 

 them. 



At the termination of about 2 years the soils were transferred 

 from the greenhouse to a coldframe. The two muck soils were 

 mixed and lime was added to raise the pH to a range of 6.3 to 6.6. 

 It will be seen in the section describing the coldframe crop data 

 that the limed, DDT-treated muck mixture was rather highly toxic 

 to the plants at the 400- and 1,000-pound levels of DDT. 



Table 3 was prepared from the same data that were used in the 

 preparation of tables 1 and 2. The figures for the several species 

 in a group of plants were combined for each DDT treatment of 

 each of the four soils. The table shows that among the three 



