Pungency of Red Radish Storage Roots Is Unaffected by Spent Mushroom Substrate or Yard Waste Compost Treatments Used for Field Production

Field experiments were conducted at Bixby, OK, in 2007. Four compost treatments and an unamended control were compared for field production of eight (spring) or four (fall) red radish (Raphanus sativus L.) cultivars. Treatments were either spent mushroom substrate or yard waste compost spread over plots to an average depth of 2.5 or 5 cm and preplant-incorporated to approximate to 5 to 7 cm deep. Radishes were direct-seeded into prepared plots and subsequently grown using standard cultural practices. Samples of median-sized marketable storage roots were shredded and juice was analyzed in the laboratory for pungency as measured by isothiocyanate (ITC) concentration (primarily 4-methylthio-3-butenyl isothiocyanate). In the spring, mean ITC concentrations ranged from 28.2 to 36.8 mu mol per 100 g juice in storage roots from the four compost treatments, and differences were not significant (alpha = 0.05). There were not enough storage roots to analyze from the unamended control plots as a result of herbicide toxicity. Cultivars differed in mean concentration of ITCs, ranging from a high of 52.9 mu mol per 100 g juice for 'Cherry Belle' to a low of 19.2 mu mol per 100 g juice for 'Crunchy Royale'. In the fall, mean ITC concentrations ranged from 10.5 to 24.6 mu mol per 100 g juice in storage roots from the four compost treatments. Differences were not significant (alpha = 0.05), and there were no differences from the control value of 17.5 mu mol per 100 g juice. The mean ITC concentration was 19.9 mu mol per 100 g juice for the four cultivars tested in the fall, and the cultivars did not differ. Results indicate that the tested compost treatments did not affect pungency of red radish storage roots as measured by concentrations of ITCs.