Persistence and Effect of TMTD on Soil Respiration and Nitrification in Two Nursery Soils

Persistence of tetramethylthiuram disulfide (TMTD) and its effect on activity of soil microflora in general and on nitrifying micro-organisms in particular were investigated in soils from two tree nurseries in western Washington. TMTD was depleted in both soils; rate of depletion depended on initial concentration of the chemical and action of soil micro-organisms. Addition of some commercial fertilizers enhanced depletion. Use of these fertilizers or addition of well-decomposed organic matter in the nursery would probably increase degradation of TMTD in soil. TMTD decreased soil respiration. Soils responded differently to treatment, but initial depressions of CO2; production in both soils were proportional to concentration of TMTD in soil. Following initial inhibition in two treatments, respiration was stimulated, probably due to utilization of decomposition products of TMTD by micro-organisms. Nitrification was impaired by TMTD for 20 days but by 60 days had recovered completely in almost all cases. Effects of TMTD reaching the soil during spray operations with a repellent formulation containing the chemical do not seem serious, and even beneficial effects seem possible under some conditions.