Leaf chlorophyll content, phenolic content, flavonoid content and antioxidant activity of collard greens in response to fertilizer value of duckweed

Biennial collard greens (Brassica oleracea var acephala cv Morris Heading) are leafy vegetables that serve as an excellent source of phenolic and flavonoid compounds. Information concerning the supplementary effects of duckweed as a sole organic source of plant nutrition to enhance the content of certain phytochemicals in this vegetable remains limited. The research assessed the extent to which duckweed pellets and dried duckweed used as fertilizer affected the chlorophyll content of collard green leaves along with the total phenolic as well as flavonoid content and antioxidant properties of the vegetable. Assessments during consecutive dry and wet seasons were carried out from January to July 2022. The treatments comprised 330 kg of organically cultivated paddy soil (control), 300 kg of organically cultivated paddy soil supplemented with the sole dried duckweed, sole duckweed pellet and various ratios of dried duckweed (duckweed pellets). The combination of dried duckweed and duckweed pellet with organically cultivated paddy soil produced the maximum leaf chlorophyll content, greater antioxidant activity, and increased overall phenolic and flavonoid content compared to that recorded for the control in each of the seasons studied. The relationship between total phenolic content and antioxidant activity was found to be strongly positive according to Pearson correlation coefficient analysis, indicating that it contributes more antioxidant activity than total flavonoid content.