عنوان مقاله [English]
Introduction: persistence of herbicide in the environment is one of the most important consequences of the release of herbicide in the soil. This is more important particularly, in soil consumer herbicides such as metribuzin. Metribuzin is from the group of photosystem Π inhibitors and is widely used for controlling broadleaf weeds in many crops such as potatoes, tomatoes and wheat. According to available information, metribuzin has medium and high persistence in soil and the high potential for contaminating groundwater resources as well as damaging crops in the rotation. Therefore, using strategies for reducing harmful effect of this herbicide is essential. In this regard, attention to factors affecting the fate of herbicide such as evaporation, distillation, leaching, surface runoff, absorption by soil and plant matter and especially the role of chemical analysis and biodegradation is essential and has important role in management of persistence and remains of herbicide.
Materials and Methods: An experiment was conducted in completely randomized design with factorial arrangement and three replications. Treatments included the soil at two levels (sterile and non- sterile), cow manure amount at four levels (0, 1, 5 and 10 based on soil percentage weight), and soil incubation periods at 8 levels (0, 2, 4, 8, 16, 36, 64, 90 days). To perform the test, after preparing the soil to a depth of 0 to 10 cm from the place that has no history of using herbicide for at least 5 years, the soil samples were transferred the laboratory to determine the physiochemical properties. For Sterile soil, soil samples were taken at 121 ° C and 2.1 bar pressure in the autoclave for 45 minutes, and this was repeated three times. For contaminated soil to metribuzin, after preparing the soil, at interested different levels of organic fertilizers (including 50 g dry soil), the soil samples were contaminated with metribuzin at amount of 5 mg per kilogram of soil (the equivalent of 0.25mg metribuzin in 50 g soil). The sterile water at 75% field capacity soil was then added and the bottles were closed with vent aluminum paper and placed in the incubator in darkness at 27 ° C for 90 days. After leaving the soil samples at specific time periods, the extraction of metribuzin from the soil samples was stored in freezer at -25 °-C to be used for Hplc analyses.
Result: There was no difference in the several levels of organic matter. Extraction efficiency of metribuzin at levels of 1, 5 and 10% was, respectively, 92.52, 91.76 and 91.51 % compared with the control without the use of organic fertilizers (95.52). According to the results, degradation rate was more rapid in non-sterile soil, therefore, metribuzin soil residue was 59.12, 38.18 and 28.55 %, after 36, 64 and 90 days incubation period, respectively, in non-sterile soil relative to sterile soil. No significant differences in metribuzin residues in the soil, in the first days of incubation of soil samples, may be related to the lack of a history of herbicide application and need of compatibility of soil microorganisms to metribuzin. Using 1, 5 and 10 % of cow manure amendment to non-sterile soil, decreased metribuzin halflife from 85.57 days to 47.80, 57.28 and 38.08 days, respectively, and in sterile soil its half-life decreased from 83.51 to 91.03, 49.50 and 51.34 days, respectively. Khoury et al. reported that by increasing the organic matter, the half-life of metribuzin decreases. In this experiment, increasing the organic fertilizers from 0 to 25, 50.75 and 100% resulted in a reduction of half-life from 15.4 to 12.4, 9.6, 7 and 3.1 day, respectively.
Conclusion: According to the results of this experiment, addition of cow manure can increase metribuzin degradation in soil and decrease its half-life.