Effects of Organic Fertilizer Treatments and Old Humus On Thiofanox and Aldicarb Soil Metabolisms in Sugar-beets

Cow manure, pig slurry, or a mixture of both were applied on field plots of a sugar beet trial, 1 month before sowing and an insecticide thiofanox soil treatment. During the first 2 months crop period, the S-+SO-+SO2-thiofanox soil half-lives were about 43 days in the organic fertilizer treated plots and 24 days in the organic fertilizer untreated control plots. In another sugar beet trial, soil was treated at sowing with the insecticide aldicarb, and the field was divided into two parts. The first part had been treated with cow manure in the autumn preceding sugar beet sowing; its organic matter concentration was 2.4%; that cow manure treatment had been repeated every 3 years for 18 years. In the second part, the soil contained a high concentration of old soil organic matter, humus (4.3%); this corresponded to a meadow ploughed 18 years ago; since then, no organic fertilizer had been applied. During the first 2 months crop period, the S-+SO-+SO2-aldicarb soil half-lives in the first and second part of the field were 63 and 29 days, respectively. The results show that the recent soil organic matter slows down insecticide soil metabolisms, and increases their protection efficiencies. However, the old soil organic matter, humus, had no significant effect on biodegradation, in spite of its high soil concentration.