The Effect of Organic Matter, Salinity and Soil Texture on the Degradation Rate of Glyphosate and Tribenuron-methyl Herbicides

The persistence of herbicides in soil is strongly influenced by soil properties, yet limited information is available for arid agricultural systems. This study evaluated the effects of soil organic matter, salinity, and texture on the degradation of glyphosate and tribenuron-methyl under laboratory conditions. A factorial experiment was conducted in a completely randomized design with three replications. Treatments included four sources of organic matter (municipal waste compost, vermicompost, cow manure, pistachio pulp), two application rates (30 and 50 t ha⁻ 1 ), two soil textures (sandy loam and clay loam), three salinity levels (0, 1500, and 3000 mg NaCl kg⁻ 1 soil), and two herbicides. Herbicide residues were quantified 70 days after application using HPLC. Results showed that degradation rates were significantly higher in clay loam compared to sandy loam soil. Increasing soil salinity reduced herbicide degradation, particularly in sandy loam, whereas this effect was less pronounced in clay loam. Organic matter type also played a critical role: vermicompost reduced degradation due to high adsorption capacity, while pistachio pulp and cow manure enhanced herbicide dissipation. Increasing organic matter content from 30 to 50 t ha⁻ 1 significantly accelerated degradation of both herbicides. Overall, tribenuron-methyl degraded more rapidly than glyphosate. The findings highlight the importance of soil texture, salinity, and organic amendments in regulating herbicide persistence. Moreover, pistachio pulp, an abundant agricultural by-product in Iran, demonstrated potential as a sustainable soil amendment to enhance herbicide degradation and reduce environmental risks. Highlights • The persistence of glyphosate and tribenuron-methyl herbicides was investigated under soil texture, types of organic matter and soil salinity. • The amount of organic matter and soil texture are key factors that determine the stability of herbicides in the soil. • The decomposition of herbicides was more pronounced in less salinity, clay with high organic matter. • Glyphosate herbicide was more stable than tribunurono-methyl in the soil at all treatments. • The degradation of herbicides in pistachio pulp did not vary significantly from manure and compost, thus, pistachio pulp can be seen as one of the biological filter systems in soil.