lyphosate-based herbicide increases nutrient content in earthworm casts of three species in Nigeria

Despite the impact of glyphosate-based herbicides (GBHs) on earthworm species beingrecognised, little attention has been given to the possible effects of GBH on the quality of their casts. This study investigated the quality of surface casts produced by three earthworm species (Alma millsoni, Eudrilus eugeniae andLibyodrilus violaceus) exposed to a GBH. A total of 20 buckets containing 20 adult earthworms of each species were sprayed with 115.49 ml/m² of Roundup® Alphée (Exposed),while another 20 bucketsper earthworm species were sprayed with water (Control). Casts produced by the earthworms were collected for 1st, 2nd, 4th, 6th and 8th week post-herbicide application and analysed for their quality (physico-chemical properties, minerals and metals) using standard methods. Glyphosate residue was also monitored in the cast, soil, earthworms, and weed plants from each bucket. Casts produced by the earthworms exposed to GBH were significantly higher in physico-chemical parameters and mineral contents comparedto the control casts (P < 0.05). Metals such as iron and manganese were higher in casts produced by the exposed earthworms compared to those in castsproduced by the unexposed earthworms. Varying concentrations of glyphosate, which appearto be time-dependent and species-specific, were observed in the soil, cast, earthworms and weed plants from the buckets. Surface casts produced by earthworms exposed to GBH were higher in nutrients and, of higher quality than the casts produced by the unexposed earthworm species