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Glucosinolates (GSLs) are produced by plants of the Capparales order. Upon enzymatic hydrolysis the GSLs can be transformed to the toxic isothiocyanates (ITCs), which can be used as biofumigants for the control of soil-borne pests. The rates of ITC formation and degradation are critical to both biofumigation and the toxicity and leaching of GSLs and ITCs in soil. Degradation kinetics of benzyl GSL and benzyl ITC in a sandy and clayey surface and subsoil at 8-9 degrees C at natural moisture contents were investigated, as was the rate of formation of ITC from the GSL. Degradation of GSL followed logistic kinetics with t 1/2 = 0.7-9.1 days. Degradation was faster in clayey soil compared to sandy soil, and faster in surface soil compared to subsoil. In surface soils, up to 25% of added GSL was detected as ITC, while only 1-6% were detected in the subsoils. ITC degradation followed first-order kinetics with t 1/2 = 0.3-1.7 days, with faster degradation in subsoils than in surface soils. Based on the data for GSL hydrolysis and ITC degradation, the concentration of ITC following GSL application was successfully modeled assuming complete conversion of glucosinolate to isothiocyanate and first-order degradation of isothiocyanate.

The use of glucosinolate-containing plants as soil-incorporated biofumigants for pest and disease control has raised questions regarding the fate of glucosinolates in soil; however, no method for routine analysis of glucosinolates in soil has been reported. A simple method to extract glucosinolates from soil with quantification as desulfoglucosinolates by HPLC is presented. The method involves two extractions with 70% methanol at room temperature, centrifugation, and filtration prior to the desulfation step. The desulfoglucosinolates are then quantified by HPLC using established protocols for plant tissue analysis. There were no significant interfering peaks from the soil extracts, and the method provided high extraction efficiencies (around 100%) for both aromatic (benzyl) and aliphatic (2-propenyl) glucosinolates when amended at a wide range of realistic field soil concentrations (1.6-120 nmol/g of soil). The method was equally effective in three diverse Australian soils that varied in organic matter, clay content, and pH. The method was effective in air-dried or field-moist soil, although evidence for rapid glucosinolate degradation in field-moist soil indicates that extraction of moist soils should be performed as soon as possible after sampling. The method is compatible with field soil sampling at remote sites and utilizes the same equipment and protocols already established for plant tissue analysis. Extraction of glucosinolates in the field following incorporation of Indian mustard (Brassica juncea) and rape (Brassica napus) green manure crops was also tested. Eight different glucosinolates contained in the plant tissues were identified and quantified in soil extracts at concentrations ranging from 0.11 to 21.7 nmol/g of soil.

The herbicide glyphosate and inorganic phosphate compete for adsorption sites in soil and on oxides. This competition may have consequences for the transport of both compounds in soil and hence for the contamination of groundwater. We present and evaluate six simple, kinetic models that only take time and concentrations into account. Three of the models were found suitable to describe the competition in soil. These three models all assumed both competitive and additive adsorption, but with different equations used to describe the adsorption. For the oxides, three additional models assuming only competitive adsorption were also found suitable. This is in accordance with the observation that the adsorption in soil is both competitive and additive, whereas the adsorption on oxides is competitive. All models can be incorporated in transport models such as the convection-dispersion equation.