Defoliation timing for optimal leaf nutrition in dual-use amaranth production systems

BACKGROUND: Amaranth leaves can provide important nutrients to small-scale farming families growing amaranth for seed. Amaranth is known to be tolerant to defoliation, but there is little guidance on when defoliation should be performed for optimal nutritional benefits. This series of experiments assessed tolerance to defoliation at different points throughout the vegetative stage of development, in addition to the nutritional benefits and flavor of amaranth leaves at each stage. RESULTS: Overall, timing of defoliation had no impact on seed yield or quality. Fifty percent defoliation at any point did not significantly reduce seed yield, whereas 100% defoliation throughout development reduced seed yield. The nutritional value of amaranth leaves differed substantially throughout development, with the highest concentrations of iron mid-way through vegetative development, and the highest levels of vitamin A, magnesium, and copper at the end of the vegetative development stage. Palatability was highest in young leaves, and decreased as plants aged. We also found that neither timing nor intensity of defoliation had an influence on branching, which can negatively influence ease of harvest. CONCLUSIONS: These results indicate that amaranth leaves are a nutritious food source that provides vital nutrients at different concentrations throughout development. Farmers who wish to harvest both leaves and seeds can harvest up to 50% of the leaves at any point during vegetative development or bud formation while maintaining seed yield. Leaf harvest timing can thus be tailored to nutritional needs, although palatability decreases with plant age. © 2020 Society of Chemical Industry.