Laboratory and field studies on metribuzin persistence in soil and its prediction by simulation models

Abstract

Metribuzin degradation rate was determined in three soils by laboratory experiments under controlled conditions. Degradation in all soils closely approximates first order kinetics. Adsorption isotherms were calculated in the same soils using the batch equilibration method and results fitted the linearized Freundlich equation with slopes ranging from 0.67 to 0.84 and K_foc (mg^1–1/n kg^‐1L¹/ ⁿ ) values from 27 to 38. Field experiments were conducted at three locations in Spain in different seasons: winter in field A under wheat, summer in field B under tomato and summer and early spring in field C. Field half‐lives obtained were 52 days in field A, 16 days in field B, and 25 and 51 in field C in summer and spring, respectively. Two versions of a deterministic solute transport model were applied: a version with a mechanistic approach (LEACHP) and a version with a functional approach (LEACHA). Parameters derived from laboratory studies were used in the simulation. LEACHP simulations of metribuzin contents in the surface layer (0–10 cm) closely approximate actual values in all the experiments, but simulation of subsurface contents (10–20 cm) were less accurate. LEACHA simulations in the surface layer also agreed with actual contents except in the summer experiment in field C and in the first months of field B experiment. Subsurface contents were in general accurately simulated by LEACHA.

Keywords:

• Metribuzin
• Persistence
• simulation
• adsorption
• soil

Notes

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