Effects of soil and foliar applications of iron with or without nitrogen on production and nutritional quality of broccoli (Brassica oleracea var. italica)

Abstract

Context Iron (Fe) is an essential nutrient; however, it is deficient in the diets of millions of people globally, resulting in anaemia. Agronomic biofortification has been shown to be effective in alleviating Fe deficiency. Aims We evaluated the efficacy of soil and foliar applications of Fe with or without nitrogen (N) on floret and plant yield, and nutritional properties of broccoli (cv. Parthenon), in order to assess biofortification potential. Methods A greenhouse experiment comprised seven treatments: (1) control, no Fe or N application; (2) soil application of Fe (10 mg FeSO4.7H2O/kg before transplanting); (3) soil application of Fe + foliar application of N (0.4% (w/v) calcium ammonium nitrate at floret emergence); (4) foliar application of Fe (0.5% (w/v) FeSO4.7H2O at floret emergence); (5) foliar applications of Fe and N; (6) soil + foliar applications of Fe; (7) soil application of Fe + foliar applications of Fe and N. Key results Foliar Fe application with N and/or with soil Fe significantly increased commercial floret weight relative to the control (>62.5 vs 46 g), whereas treatments without foliar Fe (i.e. soil Fe alone or with N) did not differ from the control. Similarly, treatments with foliar Fe generally significantly increased floret diameter, whereas those without foliar Fe did not. Treatments with foliar Fe significantly increased floret Fe concentration (>10-fold), resulting in highly available Fe, with phytic acid:Fe molar ratios <0.2, and higher antioxidant activity and polyphenol content. Conclusions Foliar application of Fe, especially in combination with N, is the most efficient and effective application method, not only for biofortification purposes but also for productivity and for enhancing bioactive compounds in broccoli. Implications This study opens the door to implementation of effective and economically viable Fe biofortification programs with broccoli and other crops.