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Gal Dvorkin , M Manor, M Sibony , B Chefetz and B Rubin

Gal Dvorkin , M Manor, M Sibony , B Chefetz and B Rubin. Effects of long term irrigation with reclaimed wastewater, on the efficacy and fate of ALS inhibiting herbicides in the soil.

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Gal Dvorkin , M Manor, M Sibony , B Chefetz and B Rubin

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  1. Gal Dvorkin, M Manor, M Sibony, B Chefetz and B Rubin Effects of long term irrigation with reclaimed wastewater, on the efficacy and fate of ALS inhibiting herbicides in the soil The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel

  2. Na’an- cotton field (bi-crop), pivot irrigation 2006

  3. Main problems in Na’an field • The trifloxysulfuron that was applied twice in the highest recommended dose, was not able to control the Amaranthus palmeri. • Wheat that followed the cotton 4 months after the trifloxysulfuron application, was not damaged by residues that were supposed to remain in the soil.

  4. Trifloxysulfuron • Mainly used for POST treatments in cotton and also for weed control in sugarcane and turf. • Stable and residual in most Israeli soils (pH 7.6-7.8).

  5. Research hypothesis • The long term irrigation with RWW have caused changes in the soil (OM and microorganisms), thus decreasing the residual effect of ALS inhibiting herbicides. • The Amaranthuspalmeri population in Na’an field have evolved resistance to trifloxysulfuron.

  6. 4 DAT POST 12 DAT POST Trifloxysulfuron 30 g ai ha-1 27 DAT POST 32 DAT POST

  7. Possible elements effecting trifloxysulfuron dissipation from the soil • Enhanced leaching to deeper soil level. • Adsorption to the SOM in the soil/DOM in the RWW. • Microbial activity.

  8. a ab ab a ab ab ab b bc c Trifloxysulfuron effect on the test plant shoot weight significantly decreased after 40 days, regardless of soil sampling depth Ave. shoot FW (% of untreated control) Sampling depth (cm) DAT

  9. Iodosulfuron effect on the test plant shoot weight significantly decreased after 20 days, regardless of soil sampling depth a a a a a a a Ave. shoot FW (% of untreated control) Sampling depth (cm) b DAT

  10. Lab experiments Dose response curves: • RWW irrigated soil was collected from Na’an field, and FW irrigated soil was collected from near by field. • Both soils were air dried, sieved (5 mm), and were put in 7*7*7 (cm) plastic pots. • The pots were planted with wheat, and sprayed with trifloxysulfuron and irrigated with FW. • After 3 weeks in the screen house, plants were harvested and shoot fresh weight was recorded.

  11. RWW soil control 7.5 g ai ha-1 1.9 g ai ha-1 3.8 g ai ha-1 15 g ai ha-1 30 g ai ha-1 FW soil 1.9 g ai ha-1 3.8 g ai ha-1 30 g ai ha-1 7.5 g ai ha-1 15 g ai ha-1 control

  12. Possible elements effecting trifloxysulfuron dissipation from the soil • Enhanced leaching to deeper soil level. • Adsorption to the SOM in the soil/DOM in the RWW. • Microbial activity.

  13. Lab experiments Adsorption isotherms: • RWW irrigated soil and FW irrigated soil were collected and put in plastic tubes. • Water containing 3 ppm of trifloxysulfuron were added to the tubes, and shaked for different time intervals. • Water samples were collected, filtered and analyzed using HPLC.

  14. Trifloxysulfuron does not adsorb to the soil, but undergoes minor hydrolysis

  15. C14 trifloxysulfuron- no significant adsorption to the soil was observed after 48 hours

  16. Possible elements effecting trifloxysulfuron dissipation from the soil • Enhanced leaching to deeper soil level. • Adsorption to the SOM in the soil/DOM in the RWW. • Microbial activity.

  17. Lab experiments Soil sterilization: • RWW irrigated soil and FW irrigated soil were collected and put in plastic bags. • The soils were irrigated to 60% field capacity incubated for 24 hr, and autoclaved twice. • After sterilization/ resting period, trifloxysulfuron was applied asceptically to the soil. • Soils were put in petri dishes and planted with S. bicolor. • After 5 days incubation root length were measured.

  18. Non sterilized FW Trifloxy 75 g ai ha-1 Trifloxy 7.5 g ai ha-1 control RWW

  19. Sterilized FW Trifloxy 7.5 g ai ha-1 control Trifloxy 75 g ai ha-1 RWW

  20. When RWW soil is sterilized, there is trifloxysulfuron activity, and plant growth inhibition

  21. Conclusions (1) Long term irrigation with RWW accelerates trifloxysulfuron dissipation in the soil. (2) Adsorption to OM and enhanced leaching to deeper soil level are not of major significance. (3)Most likely, trifloxysulfuron’s dissipation is due to microbial processes in the soil.

  22. Thank you for listening Thank you to Teomim and Yafe foundation for financial support for this research Thank you to all Rubin lab crew for technical help and support

  23. Accumulating irrigation volume in the field (pivot irrigation, CM/ha)

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