Glyphosate and aminomethylphosphonic acid contents in field crops soils under various weed management practices

Abstract

To avoid yield loss in field crops associated with glyphosate‐resistant weed and changes in their population dynamics, repeated applications of glyphosate‐based herbicides (GBH) and combination with other herbicides are weed management practices (WMP) increasingly used worldwide, and particularly so in southern Quebec (Canada). These practices affect soil biological activity as well as soil functions but could also influence glyphosate and its main degradation product, the aminomethylphosphonic acid (AMPA), persistence. This study was conducted in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] field crops to evaluate the effects of single vs. repeated GBH applications, with or without the addition of other herbicides, on glyphosate and AMPA persistence in soils throughout a growing season. In corn plots, the highest glyphosate content (0.11 mg kg–1) was observed following two GBH applications combined with other herbicides (i.a. S‐metolachlor and mesotrione). In soybean plots, the highest glyphosate content (0.18 mg kg–1) was also measured following two GBH applications combined with other herbicides (i.a. imazethapyr and chlorimuron). AMPA contents in corn plots soils were similar whatever WMP employed, whereas differences were observed in soybean plots according to the WMP. Soybean plots thus seemed more responsive to variation in weed management practices than corn plots. This study highlights the persistence of glyphosate and AMPA in agricultural soils at least 8 wk after the last GBH application.

Impacts of Cropping Systems on Glyphosate and Aminomethylphosphonic Acid Contents and Microbial Community in Field Crop Soils in Quebec (Canada)

“…Glyphosate and AMPA extractions were performed according to the approach described by Samson-Brais, et al [40]. Soils were freeze-dried and crushed using a pillar and mortar.…”

“…Hence, sites with no-till practices and frequent cover crop usage (Sites G, H, and I) could result in a slower glyphosate dissipation compared to sites with tillage and lower soil cover by crop residues (Site D). Additionally, repeated GBH applications can lead to lower soil microbial activity and soil respiration [76,77], potentially inhibiting glyphosate biodegradation into AMPA [40]. Hence higher GBH applications could not directly lead to higher AMPA contents in the soil, but rather to an accumulation of glyphosate.…”