Wormcasts produced by three earthworm species (Alma millsoni, Eudrilus eugeniae and Libyodrilus violaceus) exposed to a glyphosate-based herbicide reduce growth, fruit yield and quality of tomato (Lycopersicon esculentum)

Abstract

It remains unknown if casts produced by earthworms exposed to a glyphosate-based herbicide (GBH) will retain their agricultural benefit. This study investigated the agricultural importance of surface casts produced by three earthworm species (Alma millsoni, Eudrilus eugeniae and Libyodrilus violaceus) exposed to a GBH on growth, fruit yield and quality of tomato (Lycopersicon esculentum). We sprayed 60 buckets (i.e 20 buckets/earthworm species) containing 20 adult earthworms of each species with 115.49 ml/m2 of Roundup® Alphée (Exposed) while another 60 buckets with earthworm species were sprayed with water (Control). Surface casts produced by the earthworms were collected for 1st, 2nd, 4th, 6th and 8th week post herbicide application. Tomato planting experiment on soil treated with the casts, NPK fertilizer and normal soil were grouped into 32 treatments. Tomato growth performance, yield and quality were evaluated with standard methods. Only the tomatoes planted with the casts of the exposed earthworms were unable to set fruit. There was no significant difference (p < 0.05) in yields of tomatoes planted with the control casts of E. eugeniae and A. millsoni compared to those planted with fertilizer. Vitamin C and β-carotene contents increased in fruits of tomatoes planted with control cast of A. millsoni while reductions were recorded in the fruits of tomatoes planted with the control casts of E. eugeniae and L. violaceus relative to those planted with fertilizer. Surface casts of earthworms exposed to GBH could not enhance tomato growth while casts produced by unexposed earthworms greatly improved the performance of tomato plant.