2 CIRCULAR 862, U. S. DEPARTMENT OF AGRICULTURE 



parathion. The period covered by this report extended through 

 May 1949. 



Most of the work involved the growing of a large number of 

 crops and varieties from seed sown in replicated small plots of 

 treated soils in benches in the greenhouse and noting the effects 

 of treatment on germination, stand, and growth of young plants. 

 The numerous crops were grown in the greenhouse in rapid suc- 

 cession; most of them were harvested and the average plant 

 weights were determined about a month to 6 weeks after planting. 



Studies of effects of DDT were conducted on four soils in the 

 greenhouse : Chester loam, Sassafras sandy loam, Evesboro loamy 

 sand, and an acid muck from New Jersey. Other substances were 

 studied only on Chester loam. 



Treatments consisted of single applications of carefully meas- 

 ured amounts of the test substance thoroughly mixed with the 

 soil of each plot. Typical treatments involved 0, 25, 100, 400, and 

 1,000 pounds per acre of DDT and of toxaphene ; 0, 100, 200, and 

 400 pounds of BHC; 0, 25, 100, and 400 pounds of chlordane; 

 and 0, 1.5, 3.0, 6.2, 12.5, 25.0, 50.0, and 100.0 pounds per acre 

 of parathion. All materials were applied on the basis of weight 

 per unit area of soil approximately 6 inches deep in the beds. 



Two years' data are presented on a field experiment with DDT 

 established in 1947 and chiefly involving replicated plots treated 

 with DDT at 0, 25, 50, 100, and 200 pounds per acre. 



Species and varieties differ markedly in their sensitivity to 

 DDT in the soil. Abruzzi and Rosen rye and Stringless Black 

 Valentine bean are among the most sensitive observed. They are 

 consistently and significantly depressed in growth by 100 pounds 

 or more of DDT per acre on mineral soils. Pound for pound, 

 DDT was much less toxic on the acid muck than on the mineral 

 soils used. Effects upon such very sensitive species were pro- 

 duced by as little as 25 to 50 pounds of DDT in carefully con- 

 trolled experiments. Other beans, beets, most legumes, cucurbits, 

 and tomatoes were moderately to highly sensitive. Most grains, 

 including corn, members of the cabbage family, and Irish potatoes 

 were moderately to highly tolerant. Two varieties of sweet corn 

 showed no reduction in growth on soil containing 1,000 pounds 

 per acre of DDT. It will require years to learn the relative toler- 

 ance of all the more important crop varieties. 



In general, DDT had but slight effect upon germination and 

 stand, even among species that are sensitive after emergence. 

 At concentrations of 400 and 1,000 pounds per acre, however, 

 stands were significantly depressed. 



DDT showed no decrease by chemical analysis or decline in 

 toxicity on mineral soils over the 4-year duration of the work 

 reported here. 



The o,p' isomer of DDT appeared about four times as toxic as 

 the p,p' isomer in limited tests. The 20 pounds of the former 

 that is present in 100 pounds of technical DDT depressed growth 

 as much as the 75 pounds of the latter. 



Technical BHC is generally harmful to germination and stand 

 of all crops tested at 400 pounds per acre. Only the more sensi- 

 tive crops were harmed at 100 and 200 pounds. It appeared 



