Falling into line: Adaptation of organically grown kale (Brassica oleracea var. acephala) and kale relatives to fall planting

■Organic agriculture requires different growing environments than conventional production.■Organic systems need cultivars adapted to organic growing conditions.■Kale is a nutritious leafy green vegetable rich in minerals and prebiotic carbohydrates.■Kale demonstrates a significant genotypic effect on biomass, minerals, and prebiotic carbohydrates.■Some kale cultivars outperform others in fall-planted organic conditions and are better suited to organic agriculture. Kale (Brassica oleracea var. acephala) is a low-calorie leafy green containing a range of minerals and prebiotic carbohydrates. Thus, the inclusion of kale in diets worldwide could have multiple beneficial health effects to combat micronutrient malnutrition and obesity. Kale cultivars adapted to conventional production record higher yields than those grown in organic growing conditions. Additionally, significant differences in nutritional quality have been reported in kale cultivars and kale relatives depending on the growing season. This study aimed to determine which kale cultivars and relatives are best suited to produce under organic growing conditions in the fall. In a randomized design, 36 kale genotypes (13 cultivars and 23 United States Department of Agriculture (USDA) germplasm) were grown under organic field conditions to determine adaptability, biomass, mineral, and prebiotic carbohydrate concentrations. Significant genotypic effects were noted for biomass, mineral nutrients, and prebiotic carbohydrates. Biomass ranged from 60–404 g/plant for cultivars and 73–506 g/plant for germplasm. A single serving of the cultivars grown in this study would provide a notable amount of the daily values of calcium (27–57%), zinc (3–7%), potassium (12–16%), magnesium (1%), manganese (104–217%), phosphorous (3–4%), iron (8–14%), and copper (4–6%). Total prebiotic carbohydrate concentrations ranged from 336 to 743 mg/100 g in cultivars and 502 to 1802 mg/100 g in germplasm. The germplasm contained significantly greater levels of the simple sugars glucose and fructose than the cultivars. The cultivars ‘Westlander,’ ‘Curly Roja,’ and ‘Scarlet’ were best adapted for fall organic production for biomass and mineral concentrations. The cultivars best adapted to organic production as identified by this study should focus on future research and breeding efforts emphasizing biomass, mineral nutrition, and prebiotic carbohydrate concentrations.