The use of glyphosate-based herbicides (GBHs) in industrial agriculture has intensified in the past decades, causing a growing concern about the occurrence and spatial distribution of glyphosate and its principal metabolite, aminomethylphosphonic acid (AMPA), in the environment. In 2014, glyphosate and AMPA content was measured in 45 soils from the St. Lawrence Lowlands (Quebec, Canada) before seeding and at harvest in soybean field crops using various weed management practices with or without GBH applications. At the same time, a recent history of agricultural practices and soil conditions was compiled for the sampled sites. The results of the study show that 91% of the samples contained detectable amount of either glyphosate or AMPA, with maximum values of 0.47 mg·kg−1 and 1.16 mg·kg−1 for glyphosate and AMPA, respectively. Surprisingly, detectable amounts of AMPA were measured in fields not treated with GBHs in 2014, whereas traces of both glyphosate and AMPA were detected in organic field crops, highlighting the potential spreading and/or persistence of both compounds in the environment. Glyphosate content was significantly higher in clay soils rich in exchangeable cations, such as Mg2+, K+ and Ca2+, which can contribute to the retention of glyphosate in soil via complexation processes.

Weed management (WM) is necessary to prevent crop losses through competition with weeds and maintain high yields. However, in the case of glyphosatetolerant (GT) crops, phytotoxic effects can occur after glyphosate-based herbicide (GBH) applications, which could impact yields and quality. In order to assess the agronomic performance of six WM strategies on GT soybean [Glycine max (L.

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.

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