Development of Protocols for Containerized Culture of Seabeach Amaranth (Amaranthus pumilus) and Nitrogen Nutrition of Southern Seaoats (Uniola paniculata) Grown in the Float System.

Abstract

Fresh seeds of seabeach amaranth (Amaranthus pumilus Raf.) were treated with K-GA3 at 0, 100, 500, or 1000 mg•L-1 for 24 hours and germinated at 25 °C or an 8⁄16-hour thermoperiod of 30⁄20 °C with daily photoperiods at each temperature of 0 (total darkness) or 16 hours. Germination was recorded every 3 days for 30 days. Nontreated seeds did not germinate. When germinated at 25 °C the response of seeds to K-GA3 was linear for both photoperiods with significantly greater total germination in the dark for seeds treated with K-GA3 at 100, 500, or 1000 mg•L-1. At 25 °C, 84% germination was observed for seeds treated with K-GA3 at 1000 mg•L-1 and maintained in darkness, whereas for seeds exposed to a 16-hour photoperiod, maximum germination was 72%. The response to K-GA3 at 30⁄20 °C was quadratic with maximum germination at predicted rates of K-GA3 at 882 and 875 mg•L-1 (93% and 91%, respectively) for photoperiods of 0 and 16 hours, respectively. Treatment of seeds with K-GA3 removed physiological dormancy. For a second study, seeds of seabeach amaranth were moist-prechilled for 90 days at 4 °C or treated with K-GA3 at 1000 mg•L-1 for 24 hours. Both groups of seeds were sown in containers of two differing volumes, 139 or 635 cm3, with a substrate of 1 peat : 1 pine bark (v/v) amended with pulverized dolomitic limestone at 2.24 or 4.48 kg•m-3. The containers were maintained in a greenhouse and after seedling emergence, seedlings were fertilized with a 20N-4.4P-8.2K acidic, water soluble fertilizer or a 15N-2.2P-12.3K basic, water soluble fertilizer. Each fertilizer was applied thrice weekly at N application rates (NARs) of 75 to 300 mg•L-1. Eight weeks after sowing, data were recorded. Regardless of fertilizer, top dry weight and leaf area of seabeach amaranth increased linearly with increasing NAR, and maximum top dry weight and leaf area occurred with N at 300 mg•L-1, whereas root dry weight was unaffected by NAR. Both fertilizers increased electrical conductivity (EC) linearly with increasing NAR, and EC values of 1.15 to 1.18 dS•m-1 should be adequate for maximum growth. Substrate pH decreased linearly with increasing NAR 21, 43, and 57 days after initiation. Top and root dry weights, and leaf area were greater for seedlings from seeds treated with K-GA3. Seabeach amaranth grown in the large containers had top and root dry weights and leaf area 61%, 33%, and 57% larger, respectively, than plants grown in the smaller container volume. Top N concentration increased linearly with increasing NAR for acidic and basic fertilizers with N concentrations of 58.4 and 50.4 mg•g-1, respectively, at maximum top dry weight. Seabeach amaranth can be produced successfully utilizing an acid or basic fertilizer having a 4.5N-1P-1.9K or 6.8N-1P-5.6K ratio, respectively. As a third experiment, seeds of southern seaoats were sown in styrofoam float trays filled with a vermiculite-based hydroponic substrate. Trays were floated in plastic tubs (one tray per tub) containing a complete nutrient solution with N at 10 to 240 mg•L-1 from a 2N-3.5P-1K ratio (8N-14.1P-4.1K) liquid slow-release fertilizer. After 10 weeks data were recorded. Total plant, top, leaf, stem, and root dry weights increased quadratically with increasing N application rate (NAR) with maximum dry weights calculated to occur with N at 140 to 150 mg•L-1, respectively. Leaf area, root length, and root area were maximized with N at 157, 140, and 140 mg•L-1, respectively. Calculated leaf N concentration at maximum top dry weight was 31 mg•g-1. Southern seaoats can be grown successfully using the float system with optimum N rates of 140 to 150 mg•L-1 provided by a fertilizer having a 2N-3.5P-1K ratio.