Microwave irradiation effects on vermicasts potency, and plant growth and antioxidant activity in seedlings of Chinese cabbage (Brassica rapa subsp. pekinensis)

Vermicasts is rich in beneficial microorganisms and plant growth factors. Unlike soils, the effect of microwave irradiation (MWI) on vermicasts potency has not been reported. This study investigated MWI effects on vermicasts potency, plant growth and biochemical activity in Chinese cabbage 'Bilko' seedlings. Fresh, moist vermicasts were microwaved at power output levels: 0, 100, 200, 300, 400 and 800 Watts (W). Water loss, nutrients and total aerobic plate content were assessed. A complete randomized design greenhouse experiment was used to evaluate seedlings growth performance and tissue bioactivity. Water loss increased from 5 mg/g (0 W) to 215 mg/g (800 W). Total dissolved solids and electrical conductivity of the vermicasts gradually increased with an increase in MWI power output level from 0 to 200 W. This was followed by a steep rise through treatment 300 W and a peak at 400 W. Total nitrogen and nitrate decreased, while ammonia-nitrogen and nitrite-nitrogen increased at higher power levels. Similarly, phosphorus, potassium, magnesium, calcium, manganese, barium and molybdenum contents increased while sodium and barium remained fairly constant. However, MWI irradiation reduced total aerobic plate count by ≥50%. Plant growth and biomass were increased by the 400 W and 800 W MWI treatments. Antioxidant activity was highest in 200, 400 and 800 W treated plants. Collectively the finding indicated that the 400 W treatment increased the bioavailability of nutrients, and represents the best option for plant growth enhancement and improved antioxidant activity.