PLANT RESPONSES TO INSECTICIDES IN THE SOIL 5 



with all chemicals that are applied to crops. In this circular the 

 data obtained from the summer of 1945 to the summer of 1949 are 

 summarized for several series of tests with DDT, BHC, chlordane, 

 toxaphene, and parathion. 



This circular is primarily a progress report of work done on 

 response of several vegetable and field-crop plants to a number of 

 insecticides in the soil, at the Plant Industry Station, Beltsville, 

 Md., from late 1945 through the summer of 1949. The greater 

 part of the work was upon DDT. Some data were obtained in 

 similar studies upon BHC, chlordane, toxaphene, and parathion, 

 with some few observations on specific isomers and impurities 

 of DDT. New studies involving additional substances were ini- 

 tiated in the summer of 1949. 



NATURE OF THE INQUIRY 



The parts of these investigations that are reported herein have 

 two major objectives: (1) To determine how specific crop plants 

 are affected at each of a wide range of concentrations of a par- 

 ticular chemical in the soil, supposing that chemical to be stable 

 enough to accumulate from repeated applications over a period of 

 years; and (2) to get some idea of the persistence of whatever 

 effect is produced on plants by the addition of a known amount of 

 a chemical to a soil. 



From the very nature of the problem it is hardly possible to 

 obtain many partial answers in a short time. Large amounts as 

 well as small amounts of chemicals have been applied in the many 

 treatments to determine which crops may be highly tolerant. 

 Although it is recognized that adding large amounts of DDT, for 

 example, to the soil at one dose may not produce the same plant 

 response as applying one-tenth as much each year for 10 years, 

 it is the most practical way of learning promptly how plants will 

 react to such an amount of DDT in the soil. In view of the 

 apparent chemical stability of -DDT, BHC, and some other com- 

 pounds the large amounts added in certain of these experiments 

 are of considerable practical importance. If their apparent sta- 

 bility is confirmed, large and harmful residues of some substances 

 may accumulate in as short a time as 5 years under some condi- 

 tions of heavy use, as on orchards, on cotton, and on some truck 

 crops grown under intensive succession-cropping systems. 



REVIEW OF LITERATURE 



Arsenical Residues 



Crop injury associated with accumulation of arsenic spray or 

 dust residues in orchard or field soils has been studied by many 

 workers since the early 1900's. 



Headden (21), Vandecaveye and others (4-3), Jones and Hatch 

 (23, 24>), Morris (31), Snyder (41) , Blodgett (If), and Vin- 

 cent (H) have all dealt with toxic accumulations of arsenic in 

 orchard soils of the West. Their several findings showed that 

 arsenic accumulations in the surface soil were largely responsible 

 for increasing difficulties in the growing of certain cover crops, 

 although the deep-rooted orchard trees remained unharmed. Most 



