Optimizing germination and growth of greenhouse hydroponic baby spinach via substrate moisture, active aeration, and nitrogen concentration

Abstract

Uniform germination is essential for hydroponic baby spinach (Spinacia oleracea) production, yet poor and inconsistent seed germination remains a common problem. This study examined how the initial substrate moisture affected seed germination and how nutrient solution active aeration and nitrogen concentration influenced subsequent growth. Seeds of four cultivars (‘Corvair’, ‘Kolibri’, ‘Seaside’, and ‘Space’) were sown in foam trays filled with a peat-perlite substrate at four initial moisture indices [weightwater ÷ (weightwater + weightsubstrate)] of 0.33, 0.50, 0.67, and 0.75. Trays were incubated in darkness at ≈95.7 % relative humidity for 5 days, then transferred to greenhouse deep-water culture for 15 days at ≈21.2 °C air temperature and ≈40.7 % relative humidity under sunlight with supplemental lighting (daily light integral ≈17.3 mol m−2 d−1, 16-h photoperiod). During this phase, plants were grown in a split-split-plot randomized complete block design, with 12 flood tables divided into two blocks, receiving six nutrient solution treatments (125, 175, or 225 mg L−1 nitrogen × with or without active aeration). Germination improved with decreasing substrate moisture index; at 0.33, all cultivars showed higher germination than at 0.67 or 0.75. ‘Kolibri’ had the highest germination (87 %) at 0.33 by day 8. Trays with higher germination also produced greater total shoot fresh mass. Active aeration increased individual shoot fresh mass by 59 %–143 % and enhanced total yield, while nitrogen concentration above 125 mg L−1 provided little or negative benefit. Overall, a low initial substrate moisture index (0.33) enhanced germination, and post-germination growth was optimized by active aeration and moderate nitrogen supply.