Impact of Wheat Straw Biochar Addition to Soil on the Sorption, Leaching, Dissipation of the Herbicide (4-chloro-2-methylphenoxy)acetic Acid and the Growth of Sunflower (Helianthus Annuus L.)

Biochar addition to agricultural soils might increase the sorption of herbicides, and therefore, affect other sorption-related processes such as leaching, dissipation and toxicity for plants. In this study, the impact of wheat straw biochar on the sorption, leaching and dissipation in a soil, and toxicity for sunflower of (4-chloro-2-methylphenoxy)acetic acid (MCPA), a commonly used ionizable herbicide, was investigated. The results showed that MCPA sorption by biochar and biochar-amended soil (1.0wt% biochar) was 82 and 2.53 times higher than that by the non-amended soil, respectively. However, desorption of MCPA from biochar-amended soil was only 1.17 times lower than its desorption in non-amended soil. Biochar addition to soil reduced both MCPA leaching and dissipation. About 35% of the applied MCPA was transported through biochar-amended soil, while up to 56% was recovered in the leachates transported through non-amended soil. The half-life value of MCPA increased from 5.2d in non-amended soil to 21.5 d in biochar-amended soil. Pot experiments with sunflower (Helianthus annuus L.) grown in MCPA-free, but biochar-amended soil showed no positive effect of biochar on the growth of sunflower in comparison to the non-amended soil. However, biochar itself significantly reduced the content of photosynthetic pigments (chlorophyll a, b) in sunflower. There was no significant difference in the phytotoxic effects of MCPA on sunflowers between the biochar-amended soil and the non-amended soil. Furthermore, MCPA had no effect on the photosynthetic pigment contents in sunflower.