Ionic Thiocyanate (SCN⁻) Production, Fate, and Phytotoxicity in Soil Amended with Brassicaceae Seed Meals

Abstract

Brassicaceae seed meals produce ionic thiocyanate (SCN (-)), a bioherbicidal compound. This study determined the fate of SCN (-) in a field soil amended with seed meals of Sinapis alba, Brassica juncea, and Brassica napus and quantified crop phytotoxicity by monitoring carrot ( Daucus carota) emergence. Meals were applied at 1 or 2 t ha (-1), and soils were sampled to 35 cm for SCN (-). Maximum SCN (-) (211 micromol kg (-1) of soil) was measured at 5 days in 0-5 cm samples from plots amended with S. alba meal at 2 t ha (-1). Less than 30 micromol of SCN (-) kg (-1) of soil was measured at soil depths below 15 cm. At 44 days, SCN (-) was <15 micromol kg (-1) of soil in all treatments. Emergence inhibition of carrots seeded 15-36 days after meal amendment was found only in S. alba treatments. The rapid decrease of SCN (-) concentrations in Brassicaceae meal-amended soil indicates limited potential for off-site environmental impacts.

Evaluating Mustard Seed Meal for Weed Suppression in Potato (Solanum tuberosum)

“…'Umatilla Russet' was planted in and var. 'Ranger Russet' in 2007and 2008 at a seed piece spacing of 22 cm in rows spaced 86 cm apart. Seed pieces were placed 17 cm deep with a 6-row potato planter.…”

“…MSM contains glucosinolates that typically undergo enzymatic hydrolysis to isothiocyanates, SCN2, nitriles, and other compounds when added to moist soil (Brown, Morra, McCaffrey, Auld, & Williams, 1991;Borek & Morra, 2005;Vaughn & Berhow, 2005). The predominant glucosinolate in S. alba seed is 4-hyroxybenzyl glucosinolate or sinalbin, which ultimately yields SCN2, a compound partly responsible for herbicidal activity of MSM (Daxenbichler, Spencer, Carlson, Rose, Brinker, & Powell, 1991;Borek & Morra, 2005;Hansson, Morra, Borek, Snyder, Johnson-Maynard, & Thill, 2008). MSM applied at rates ranging from 113 to 450 g m -2 to the soil surface of container-grown ornamentals reduced annual bluegrass (Poa annua L.), common chickweed [Stellaria media (L.) Vill.…”

Residues of bioenergy production chains as soil amendments: Immediate and temporal phytotoxicity

“…However, in this study, biochar did not alter the fate of glucosinolate or its hydrolysis products in soil (isothiocyanate, thiocyanate, and nitrile) as phytotoxicity produced by rapeseed meal was unmodified by biochar addition. Although decrease of thiocyanate content in soil has been found to be strongly correlated to soil organic matter, it seems that sorption or degradation by abiotic processes only occur at temperatures above 30 • C, whereas microbial degradation prevails below that temperature [14,15].…”

“…Rapeseed meal has some phytotoxic properties, which are attributed to glucosinolates and their decomposition products [12,13]. As they become non-toxic within days [14,15], rapeseed meal is used on a limited scale as soil amendment for weed or pest suppression [16]. However it has also been suggested as nitrogen fertilizer [17].…”

Comparative Efficacy of White Mustard (Sinapis albaL.) and Soybean (Glycine maxL. Merr.) Seed Meals as Bioherbicides in Organic Broccoli (Brassica oleraceaVar. Botrytis) and Spinach (Spinacea oleracea) Production

“…Other studies, however, also have reported phytotoxic effects of white mustard seed meal on crops. For example, Hansson et al (2008) reported that the seedling emergence of carrot (Daucus carota L.) was inhibited by white mustard meal soil amendments. Such phytotoxic effects have been attributed to high glucosinolate content in Brassica species and to the gradual release of ionic thiocyanate (SCN − ) from the mustard meal (Borek and Morra 2005;Hansson et al 2008).…”