Brassicae crops (mustard family) contain chemicals called glucosinolates. These compounds are present in the leaves, stem, roots, and seed of the plants. When the plant biomass is incorporated into the soil these glucosinolates are broken down into a number of secondary compounds. The primary compound is isothiocyanate which can be biocidal to germinating seeds, insects, nematodes, and other microbes (fungi, bacteria, etc). In recent years, plant breeders have worked to develop high glucosinolate varieties of mustard to be used as biofumigants in crop production. These high glucosinolate mustards (HGM) are being used as cover crops and the entire plant biomass incorporated into the soil. Interestingly, the mustard is also an oilseed with a potential use in biofuel production. Extraction of the oil from the seed leaves a meal that is also high in glucosinolates as well as nitrogen. Hence, the meal used as a soil amendment could potentially provide nutrients and suppress weed and diseases.
Vermont, University of Vermont Extension
Darby, Heather; Harwood, Hannah; Cummings, Erica; and Monahan, Susan, "Impact of High Glucosinolate Mustard Biomass and Meal on Black Bean Yield" (2013). Northwest Crops & Soils Program. 33.