The effect of the annual use of pesticides on soil microorganisms, pesticide residues in the soil and barley yields

Abstract

AbstractA study has been made of the influence of pesticides used annually on soil microorganisms and crop yields. The persistence of these pesticides in the soil was also investigated. The herbicides MCPA, glyphosate, maleic hydrazide and tri‐allate, and the insecticide parathion, were applied on experimental plots on which barley was grown during the years 1973‐1981. The fungicide 2‐methoxyethylmercury chloride was used every year for dressing the seeds grown in pesticide‐treated plots. The pesticide treatments did not affect significantly the numbers of several groups of soil microorganisms. A slight increase was, however, observed in the nitrification activity in the soil. The barley yields were on average higher on pesticide‐treated plots than on controls because of successful weed control. Pesticide residues in the soil were generally very low; for example, for parathion they were below 0.02 mg kg−1 within 11 days, and for MCPA 0.06 mg kg−1 within 7 days. However, the glyphosate residue was 1.6 mg kg−1 in the autumn 2 days after the treatment, and the residue settled to a level of 0.2 mg kg−1 during the following summer. No clear dependence was observed between the residue level and the time between treatment and sampling.