Chemical composition of kale as influenced by dry vermicast, potassium humate and volcanic minerals.

Biofortification using agronomic practices can be used to improve the nutritional quality of food crops. Three natural media amendments (dry vermicast, potassium (K)-humate and volcanic minerals) were assessed under greenhouse conditions to determine the effects on the chemical composition of kale (Brassica oleracea L. var. acephala 'Ripbor'). The results indicated that K-humate had low pH, while the volcanic minerals had high pH. Plants grown in the dry vermicast amended media had the highest levels of macronutrients and micronutrients except for zinc and iron. However, the glycolipid: phospholipid ratio was lower in kale plants cultivated in dry vermicast compared to plants cultivated in the volcanic minerals or K-humate. Conversely, plants cultivated in the dry vermicast had enhanced levels of polyunsaturated fatty acids. The omega-3 fatty acid content was significantly (P < 0.05) higher in plants cultivated in dry vermicast and potassium humate, while the omega-6 fatty acids were unaffected by media amendments. Dry vermicast was the most effective at increasing plant tissue oleic acid content. The total phenolic content and antioxidant capacity were highest in plants treated with K-humate, but lowest in the dry vermicast treated plants. In conclusion, dry vermicast proved to be the most effective in enhancing the phytochemical composition of kale 'Ripbor'. These results suggest dry vermicast could be a potential target natural media amendment for biofortifying kale plants during cultivation.