Effects of pesticides on soil microflora using dalapon as an example

Effects of the herbicide dalapon on the soil microflora are evaluated. Measurements were made on populations and pure cultures of micro-organisms, dehydrogenase and phosphatase, soil respiration, and nitrogen transformations. At normal concentrations of 2.6 and 26 ppm, dalapon had little effect and is unlikely to harm the soil microflora or soil fertility. At abnormal concentrations of 266 and 2,660 ppm, marked effects occurred on the microflora and its activities. In one soil, 2,660 ppm dalapon significantly increased production of ammonium-nitrogen; nitrification was almost totally inhibited in this soil. The results are discussed in terms of the validity of the tests for detecting effects of pesticides on the soil microflora. Some problems, particularly of data interpretation and evaluation, are high-lighted.