Glyphosate spraying and earthworm Lumbricus terrestris L. activity: Evaluating short-term impact in a glasshouse experiment simulating cereal post-harvest

Abstract

A glasshouse experiment was conducted to study if glyphosate spraying has immediate short-term effects on the growth, reproduction and residue incorporation of the earthworm species Lumbricus terrestris L. The experiment simulated post-harvest conditions in no-till cereal cultivation, where L. terrestris often abound, and glyphosate is widely used. Pairs of adult, field-collected L. terrestris (median total mass 11.2 g fresh weight) were kept in fine sand-filled cylinders, with chopped wheat straw on the soil surface as feed. The treatment cylinders were sprayed with glyphosate at normal field application rate [Rodeo® XL 3.0 l ha−1, resulting in 1080 g a.i. ha−1 and “Contact” surfactant (0.5 l ha−1)]; the controls were sprayed with water (N = 12 for both). The treatment and control cylinders were maintained for two months at +15 °C, approximate 60% air humidity and 12h:12h light:dark cycle. All individuals survived the experiment. There was no difference in L. terrestris mass change over the experiment, with an average weight change of +0.96% in glyphosate treatment and −0.93% change in the control (p = 0.66). Glyphosate treatment and control did not differ in cocoon production rate (31 vs 28 cocoons cylinder−1 respectively; p = 0.30). The straw incorporation was slightly but not significantly lower in glyphosate-treated soil (decline in surface straw mass 27.5% vs. 30.5%; p = 0.07). The glyphosate treatment applied represents a commonly used practice in spring cereal cultivation, and it did not affect negatively L. terrestris. The varying study results on the effects of glyphosate on earthworms – and on L. terrestris in particular – may partly arise from notable variation in application rates and the formulation-surfactant combinations used in different experiments which needs to be considered in the ecological risk assessment of glyphosate use.