Sources and fate of glyphosate and aminomethylphosphonic acid in field crops soils

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The usage of glyphosate-based herbicides (GBH) in association with glyphosate tolerant crops increased exponentially in field crop agriculture throughout the world for the past two decades. Consequently, glyphosate and its main degradation product, aminomethylphosphonic acid (AMPA), are ubiquitously detected in the environment. The long-term vision of this DG research program focuses on understanding the dynamics of glyphosate and AMPA with respect to various agricultural practices, and on identifying the role played by the soil biotic and abiotic constituents in degrading, remobilizing or accumulating, those chemicals. Ultimately, it is intended to highlight best practices in conservation agriculture limiting GBH usage while enhancing GBH degradation. The present Discovery research program is based on two analytical breakthroughs developed in my Environmental Geochemistry Laboratory, i.e. routinely analyzing traces of glyphosate and AMPA in soils and plants using a GC-ECD, and measuring compound-specific d13C of glyphosate and AMPA with a newly acquired LC-IRMS. Three complementary short-term research objectives will be pursued throughout the program with the benefit of long-term collaboration with farmers: 1) Estimate the degradation and persistence of glyphosate and AMPA in soils. To do so, laboratory and open field experiments will be conducted to follow along with agricultural operations the evolution of glyphosate and AMPA contents and d13C signatures in soils. 2) Evaluate the respective soil inputs of glyphosate and AMPA by GBH and biosolids. Wastewater biosolid amendments could represent a source of glyphosate and AMPA to soils. An experimental setting using GBH lots with a glyphosate d13C signature distinct from that of glyphosate and AMPA in biosolids should allow distinguishing the relative dynamics of both compounds brought to agricultural soils either by biosolids or by GBH. 3) Identify the source of glyphosate and AMPA in organic farming systems. Glyphosate and AMPA are detected in soils of long-established organic field crop systems. Measurements of glyphosate and AMPA d13C signatures in various farm inputs such as manure will allow identifying the sources and persistence of these compounds in organic farming soils. Using GBH to control weeds with no-till practices, and / or recycling municipal biosolids as fertilizer residual are presented as management practices keeping or restoring soil functions, maintaining biodiversity and fighting climate change. This argument towards sustainability of field crops systems is only valid if glyphosate and AMPA's persistence in soil is short. Understanding the mechanisms responsible for the dissipation of these chemicals in soils is thus of utmost importance. The program will offer a stimulating environment for HQP, combining training on sophisticated analytical techniques with the broad understanding of complex and strategic agri-environmental issues.