title: Varying plant density and harvest time to optimize cowpea leaf yield and nutrient content.
abstract: Plant density and harvest time were manipulated to optimize vegetative (foliar) productivity of cowpea [Vigna unguiculata (L.) Walp.] canopies for future dietary use in controlled ecological life-support systems as vegetables or salad greens. Productivity was measured as total shoot and edible dry weights (DW), edible yield rate [(EYR) grams DW per square meter per day], shoot harvest index [(SHI) grams DW per edible gram DW total shoot], and yield-efficiency rate [(YER) grams DW edible per square meter per day per grams DW nonedible]. Cowpeas were grown in a greenhouse for leaf-only harvest at 14, 28, 42, 56, 84, or 99 plants/m2 and were harvested 20, 30, 40, or 50 days after planting (DAP). Shoot and edible dry weights increased as plant density and time to harvest increased. A maximum of 1189 g shoot DW/m2 and 594 g edible DW/m2 were achieved at an estimated plant density of 85 plants/m2 and harvest 50 DAP. EYR also increased as plant density and time to harvest increased. An EYR of 11 g m-2 day-1 was predicted to occur at 86 plants/m2 and harvest 50 DAP. SHI and YER were not affected by plant density. However, the highest values of SHI (64%) and YER (1.3 g m-2 day-1 g-1) were attained when cowpeas were harvested 20 DAP. The average fat and ash contents [dry-weight basis (dwb)] of harvested leaves remained constant regardless of harvest time. Average protein content increased from 25% DW at 30 DAP to 45% DW at 50 DAP. Carbohydrate content declined from 50% DW at 30 DAP to 45% DW at 50 DAP. Total dietary fiber content (dwb) of the leaves increased from 19% to 26% as time to harvest increased from 20 to 50 days.
authors.affiliation: National Aeronautics and Space Administration Specialized Center of Research and Training in Bioregenerative Life Support, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: Ohler
authors.forename: S S
authors.initials: SS
authors.lastname: Nielsen
authors.forename: C A
authors.initials: CA
authors.lastname: Mitchell
mesh_terms: D018533:Biomass; D002241:Carbohydrates / Q000032:analysis; D004043:Dietary Fiber / Q000032:analysis; D018504:Ecological Systems, Closed; D007887:Fabaceae / Q000737:chemistry / Q000254:growth & development*; D005223:Fats / Q000032:analysis; D008021:Life Support Systems; D009753:Nutritive Value; D018515:Plant Leaves / Q000737:chemistry / Q000254:growth & development*; D014674:Plant Proteins, Dietary / Q000032:analysis; D010946:Plants, Medicinal; D013997:Time Factors
chemical_list: D002241:Carbohydrates; D004043:Dietary Fiber; D005223:Fats; D014674:Plant Proteins, Dietary