, Volume 107, Issue 2, pp 149-158

Fate of [carbonyl-14C]methabenzthiazuron in an arid region soil — effect of organic amendment, soil disturbance and fumigation

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[Carbonyl-14C] methabenzthiazuron (MBT) was applied to an arid region soil at a rate of 5mg kg−1 soil to give a14C content of 2400 KB kg−1 soil. After 15 weeks of incubation at 22°C and 50% of the maximum water holding capacity of the soil, 7.2% of the applied14C was mineralized to14CO2. Where the soil was amended with wheat straw, total mineralization increased to 17.3%. Soil disturbance caused a significant increase while chloroform fumigation caused a significant decrease in the rate of14CO2 production, both from amended and unamended soils. These results suggest that MBT is degraded mainly through microbial co-metabolism.

Wheat straw amendment resulted in increased transformation of MBT into soil humus. In unamended soil, a major portion of14C was recovered in fulvic acid and in fractions extracted with organic solvents. Recovery of14C in non-extractable bound residues (humins) increased as incubation progressed and seemed to be derived from the fulvic acid fraction, which showed a concomitant decrease.

More than 99% of the residual14C in unamended soil consisted of unaltered MBT; the remainder occurred as 1-methyl-1 (benzthiazolyl) urea. In amended soil, a relatively higher percentage of the extractable14C was found in the metabolite. Small amounts of three unidentified14C-labelled compounds were also observed.

In amended soil, disturbance caused a decrease in extractable-14C whereas fumigation caused a significant increase, as compared to the untreated control. The effects were more pronounced when the soils were reated at an early stage of incubation. In general, soil disturbance increased the availability of MBT for further transformations while chloroform fumigation decreased the process.