Effects of some organophosphate and carbamate insecticides on nitrification and legume growth

Summary Nine insecticides (six organophosphates and three carbamates) were tested for their effects on soil nitrification, growth of legume seedlings, and growth of four species of rhizobia bacteria. No inhibition of nitrification was found at normal field rates (5 ppm) of application. Some instances of inhibition were observed at 50 ppm and at 500 ppm. Similarly, 5 ppm applications did not inhibit growth of alfalfa or sweetclover seedlings ... with one exception. Disc inhibition tests of the rhizobia bacteria showed thatRhizobium leguminosarum andRhizobium trifolii were most sensitive to the pesticides.Rhizobium meliloti, and particularlyRhizobium japonicum, were resistant to the insecticides. No consistent correlation was observed between tests on the nodulating bacteria and the tests on legume growth.Published with the approval of the Director of the North Dakota Agricultural Experiment Station as Journal Article No.309. Portion of a thesis presented by the senior author in partial fulfillment of the requirements for the M.S. degree in bacteriology at North Dakota State University.