34 



CIRCULAR 862, U. S. DEPARTMENT OF AGRICULTURE 



possible that DDT drip and residues from the fallen leaves had 

 accumulated under the trees to a harmful degree. Since, how- 

 ever, the weather had been unusually dry for several weeks be- 

 fore and also after the sowing of the rye, it was possible that the 

 failure was due to the serious depletion of the soil moisture in 

 the area of root spread of the trees (approximately the same as 

 the spread of the branches). 



To determine whether harmful amounts of DDT and other 

 chlorinated hydrocarbon insecticide compounds had accumulated 

 in the soil of this orchard and to eliminate water deficiency and 

 other effects as controlling factors in the tests, an experiment was 

 set up in the greenhouse in September 1949 as follows : Soil was 

 removed from beneath representative trees in the orchard to the 

 depth of 3 to 4 inches, the normal depth of cultivation on that 

 soil, a Sassafras loam. Soil was similarly removed from areas 

 between the trees where the growth of rye appeared good, and 

 a third lot of soil of the same type was removed from sites just 

 beyond the limits of the orchard. Each soil was put into a sepa- 

 rate plot at random in each of the four blocks in greenhouse 

 benches and planted with rye and wheat, essentially as described 

 for other greenhouse studies reported in this circular. 



Samples of the three lots of soil were analyzed for arsenic by 

 R. D. Chisholm, of the Bureau of Entomology and Plant Quaran- 

 tine ; for zinc by Ellsworth Shaw ; and for DDT by Viron V. Jones, 

 of the Division of Soil Management and Irrigation. The three 

 lots of soil are identified here as "under trees," "between trees," 

 and "control." 



Results 



Table 13 contains the results of the chemical analyses of the 

 three lots of soil. It appears that the known amounts of DDT 

 applied to the trees over the 3-year period were largely recovered 

 from the soil under them. The amount of DDT found between 

 the trees was small. The amount found in the controls is within 

 the limits of error. Moderate amounts of arsenic were found both 



Table 13. — Content of arsenic, zinc, and DDT in soil front peach orchard 

 that had been sjyrayed with arsenicals, zinc-lime, DDT, and BHC, Belts- 

 ville, Md., 19A9 



Substance determined 



Amount of various substances found 

 in soil from the location shown l 





Control 



Between trees Under trees 





P. p.m. 



18 



26 



3 



P. p.m. 



222 



168 



11 



P. p.m. 



385 



Zinc 3 



51 



DDT^ 



127 







i 1 pound per acre is roughly equivalent to % part per million in the surface 6 2 s inches of 

 soil. Residue accumulations under trees will be higher, and between trees lower than the rate 

 per acre because the spray materials are applied almost entirely to the trees. 



- Total estimated amount of AS2O3 equivalent applied as lead arsenate from 1936 to 1949, 

 45 pounds per acre. Analyst, R. D. Chisholm. 



3 Total estimated amount of Zn equivalent applied as zinc-lime from 1936 to 1949, 430 pounds 

 per acre. Analyst, E. Shaw. 



4 Total estimated amount of DDT applied from 1946 to 1949, 130 pounds per acre, on or 

 beneath the trees. Analyst, V. V. Jones. 



