A solid-matrix, liquid hybrid hydroponic system for establishing small-seeded crop species

Abstract

A solid-matrix-over-liquid (hybrid) growth system was developed for direct sowing of small-seeded crop species into hydroponic culture and compared for performance with a standard solid-matrix, capillary-wick hydroponic system. Seeds were sown directly onto a 3-cm (1.2-inch) deep soilless seed bed occupying 0.147 m2 (1.582 ft2) within a tray. The planted seed bed was moistened by wicking up nutrient solution through polyester wicking material from a 7.0-L (6.6-qt) reservoir just below the matrix seed bed. The hybrid system successfully grew dense [435 plants/m2 (40.4 plants/ft2)], uniform canopies of dwarf Brassica napus L. in a controlled-environment growth room. Seed yield using the hybrid system was twice that achieved with the matrix-based system. Both systems eliminated the labor needed to transplant many small seedlings from a separate nurse bed into a standard bulk liquid hydroponic system. Root-zone pH extremes caused by ion uptake and exchange between roots and unrinsed soilless media were avoided for the hybrid system by the short dwell time of roots in the thin matrix before they grew through the matrix and an intervening headspace into the bulk solution below, where pH was easily managed. Once roots grew into the bulk solution, its level was lowered, thereby cutting off further capillary wicking action and drying out the upper medium. Beyond early seedling establishment, water and nutrients were provided to the crop stand only by the bulk nutrient solution. This hybrid hydroponic system serves as a prototype for larger-scale soilless growth systems that could be developed for production of small-seeded crops in greenhouses or controlled environments.