Fertility Treatment Affects Vitamin C, Fiber, and Total Nutrient Content in Mizuna and Red Giant Mustard

Red Giant Mustard (Brassica juncea) and Mizuna (Brassica rapa var. nipposinica) plants were grown at the University of Minnesota St. Paul Campus (St. Paul, MN) in a greenhouse from December to February under an 18-hour photoperiod (natural daylight plus 50 μmol·m^-2·s^-1 high pressure sodium lighting from 0800 to 0200 HR) and a 24/13 °C day/night temperature. Plants were grown using five different fertility treatments, including four organic treatments and one conventional control (Cal Mag 15-5-15 in SunGro LC8©media), to determine their effects on Red Giant Mustard and Mizuna growth and nutrient content. Biomass yield, vitamin C and total dietary fiber varied with fertility treatment. Total dietary fiber and vitamin C levels were measured from tissue frozen at –80 °C.  Foliar nutrients (P, K, Ca, Mg, Fe, Mn, B, Cu) were determined using an inductively-coupled plasma spectrophotometer. The experiment was replicated four times in time and the experiment was duplicated. The poultry litter treatment with Sunshine Natural and Organic Planting Mix© had the highest vitamin C content in both crops (16.0 mg/100 g in Mizuna and 20.8 mg/100 g in Red Giant Mustard). Both crops had similar vitamin C responses to the five fertility treatments, but were not associated with biomass yield, and there were no positive correlations between increases or decreases in biomass yield in relation to vitamin C content. Total dietary fiber ranged from 2–4 g/100 g per sample, indicating both crops can contribute a significant fiber to the diet, compared with other leafy vegetables, such as Romaine or Iceberg lettuce. Results indicated that fertility plays a role in vitamin C synthesis and/or accumulation, both crops can contribute a moderate amount of dietary fiber to the diet, and biomass yield may not be associated with changes in vitamin C content.   Fertility effects on leaf mineral content will also be discussed.