The Duration and Effect of 2,4‐D Toxicity to Crops Grown on Calcareous Soil under Controlled Irrigation Conditions 1

EVERAL workers (1, 3, 4, 5)3 have investigated S various factors which influence the persistency of 2,4-D (2,4-dichlorophenoxyacetic acid) in soils. Results of these studies indicate that moderately high organic matter content in soils, high pH, Le., neutral to slightly alkaline, high soil temperatures, and high soil moisture, all tend to reduce the period of soil sterility or the toxicity due to 2,4-D. Kries (4) found that when lime was added to a soil and the soil 2,4-D treated, toxicity persisted longer. Earlier studies on the duration of 2,4-D in soil, conducted under greenhouse conditions at Idaho, indicated that the toxicity of 2,4-D in soil could be eliminated in a few weeks time. The toxic effects of 2,4-D rates ranging from 1 to 16 pounds per acre, applied directly to the soil, were entirely removed in periods of 1 to 6 weeks. The duration of the soil sterility was in direct relation to the quantity of 2,4-D applied. Toxicity was determined by observing the germination and growth of alfalfa, beans, corn, and wheat as compared to the performance of these crops in untreated check flats. In these greenhouse studies, the treated and untreated soil flats were watered daily and constantly maintained at a high moisture level. Greenhouse temperalures varied between 70” and 90” F. Thus the soil temperatures were constantly higher than would exist under most field conditions. The rates of dissipation of 2,4-D obtained in these studies are in general agreemen t with other studies conducted under greenhouse conditions (1, 5) . Under field conditions, quite contrary soil sterility effects from 2,4-D have been observed. Preplanting and postplanting treatments usually have affected the crop stand adversely. Fall applications, in some instances, have shown toxic effects upon various crops plantedthe following spring. Sterility from spring applications has in a few instances persisted until fall. In one instance, a summer application gave evidence of toxicity to sugar beets a year later. Preplanting and pre-emergence weed control treatments using 2,4-D have given erratic results. Dunham (2) reported good results from pre-emergence treatments in corn in the North Central States for 1947 and poor results in 1948. This reversal was attributed