Impact of litter contaminated with glyphosate-based herbicide on the performance of Pontoscolex corethrurus, soil phosphatase activities and soil pH

Abstract

The bioavailability of glyphosate from plant residues may be high in the soil matrix. In order to determine the impact of litter contaminated with glyphosate (GLY) on the growth and cocoon production of the earthworm Pontoscolex corethrurus as well as on acid and basic phosphatase activities and soil pH, a commercial glyphosate-based herbicide was applied to three types of litter mixed with soil. Earthworms from a GLY-free coffee plantation were grown for 132days in microcosms in a two-factorial design. The first factor was glyphosate (GLY; 21.6g of glyphosate per kg of litter, with two levels (−GLY, +GLY), and the second factor was type of litter (Coffea arabica, Musa cavendishii, Inga vera). All studied factors (except days*litter*glyphosate interaction) had significant effects on earthworm biomass (P<0.05). Treatments with Coffea and Musa litter -GLY had significantly higher biomass (P<0.05), whereas treatments with Inga litter -GLY and +GLY had the lowest biomass. A decline in earthworm biomass was detected in all treatments with glyphosate (+GLY) after 72days. No significant effect on cocoon production was detected for the main factors or their interaction. Litter type showed a marginal effect (P=0.06); the average (±SE) number of cocoons decreased from Musa (5.8±2.9) to Coffea (1.3±0.56) and Inga (0.17±0.17). Soil pH significantly (P=0.006) decreased at the end of the experiment from 4.4±0.17 in -GLY to 3.9±0.06 in +GLY. Acid phosphatase activity increased in treatments with Musa and Inga +GLY (P<0.05), while alkaline phosphatase activity in the same substrates was higher in treatments with -GLY (P<0.05). We conclude that repeated application of litter contaminated with glyphosate negatively affects earthworm vitality and increases soil acidity and acid phosphatase activity.