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Soil and Environmental Health After Twenty Years of Intensive Use of Glyphosate

Monsantos RoundUp herbicide on a store shelf

Glyphosate [N (phosphonomethyl)glycine], the active ingredient of formulated herbicides including Roundup and others, is the most widely used herbicide compound in the world for vegetation management in agricultural, urban/suburban, aquatic, publically-held, and recreational ecosystems. The herbicide became very popular for non-selective weed management used in burndown or knockdown applications in field preparation prior to implementing conservation tillage systems, including no- or zero-tillage practices, that were initiated as alternatives to intensive tillage methods of moldboard plowing and disking in the late 1970’s. As agriculture shifted toward large-scale production of commodity crops on wide expanses of land, major crops were genetically engineered (GE) to resist the herbicidal action of glyphosate so that weed management could be streamlined by using only one herbicide to control all weed species present in fields thereby simplifying production practices for large-scale crop production systems. The first GE crops with glyphosate resistance included soybean (Glycine max [L.] Merr.), maize (Zea mays L.), cotton (Gossypium hirsutum L.), and canola (Brassica rapa L.), which were introduced and commercially planted in the mid-1990’s. Subsequently GE varieties were released for sugarbeet (Beta vulgaris L.) and alfalfa (Medicago sativa L.). Meyers et al. [1] describes the continuing increase in use of glyphosate in the United States alone, from an annual usage of 2.72 to 3.62 million kg in 1987 prior to release of GE crops, to 81.6 to 83.9 million kg in 2007 when glyphosate-resistant crops were widely planted. By 2014, annual agricultural usage of glyphosate increased to about more than 108 million kg applied to the environment. Worldwide use is estimated to be 1.35 million metric tons in 2017 [2].