Comparative Yield Response of Lettuce to a Commercial Seaweed Extract in Two Hydroponic Systems: A Preliminary Evaluation

Small-scale limited resource hydroponic growers continually seek new strategies to improve the production efficiency and yield of their crop plants. Two hydroponic experiments were conducted to test the effects of a proprietary extract from the brown seaweed Ascophyllum nodosum (Simplex™; Acadian Agritech, Nova Scotia, Canada), which has been reported to improve the growth of horticultural crops–on the yield of two lettuce (Lactuca sativa L.) cultivars (Concept and Nevada). Lettuce seedlings were transferred into either an Ebb-N’ Flow (Ebb&F) or Nutrient Film Technique (NFT) hydroponic system at the two-leaf stage, and grown until market maturity. The nutrient solution treatments comprised of a commercial fertilizer (15N–2.2P–12.5K plus micronutrients) at 200 mg N/liter (N₂₀₀), 150 mg N/liter (N₁₅₀) and 150 mg N/liter plus 0.5 ml Simplex™/liter (N₁₅₀+S). Ambient maximum/minimum (day/night) temperature and RH of the greenhouse during the cropping cycles were 26.6/12.2 °C and 77.5/34.5%, respectively, during October–December for the Ebb&F experiment; and 28/18 °C and 82/42.0%, respectively, during August–October for the NFT experiment. Nutrient solution pH was maintained within 6.5–7.2 with sulfuric acid, and EC ranged from 1.38–1.98 mS/cm for both Ebb&F and NFT systems. In Ebb&F, ‘Concept’ had consistently higher head fresh weight (HFW) and dry weight (HDW) than ‘Nevada’ (P = 0.05). The N₁₅₀+S treatment increased HFW over N₂₀₀ and N₁₅₀ by 15% and 20%, respectively; and HDW over N₁₅₀ (P = 0.05), but head dry: fresh weight ratio (HDWR) was higher at N₂₀₀ than either N₁₅₀ or N₁₅₀+S (P = 0.05). With ‘Nevada’, N₁₅₀+S increased HFW and HDW over N₁₅₀ (P = 0.05), however, there were no differences in HFW or HDW between N₁₅₀+S and N₂₀₀. HDWR was significantly higher at N₂₀₀ than either N₁₅₀+S or N₁₅₀ (P = 0.05). In NFT, there was no cultivar effect on HFW (P = 0.05), but ‘Concept’ had significantly higher HDW and HDWR than ‘Nevada’ (P < 0.0001). Similarly, HFW of 'Concept' was higher with N₁₅₀+S than N₂₀₀ and N₁₅₀ by 14% and 24%, respectively; and HDW was increased over N₁₅₀ by 16% (P = 0.05), however, HDWR was lower with N₁₅₀+S than either N₂₀₀ or N₁₅₀ (P = 0.05). With ‘Nevada’, N₁₅₀+S increased HFW and HDW over N₁₅₀ (P = 0.05), however, there were no differences in HFW or HDW between N₁₅₀+S and N₂₀₀. Unlike ‘Concept’, neither nutrient solution level nor addition of Simplex™ had any effect on the HDWR of 'Nevada' (P = 0.05).