The Effects of Daily Light Integral and Nutrient Solution Concentration on Growth of Several Basil Species (Ocimum spp.)

Basil (Ocimum L. spp.) is an herb commonly produced in hydroponic greenhouses. Nutrient solution concentrations are selected based on crop species, stage of growth, and environmental conditions. We have not found recommended nutrient solution concentrations for different basil species. Our objective was to quantify the effect of mineral nutrient concentration of a nutrient solution on the growth of basil species and cultivars grown under high and low daily light integrals (DLIs). Seeds of four cultivars: sweet basil (Ocimum basilicum L. ‘Nufar’), holy basil (O. tenuiflorum L. ‘Holy)’, lemon basil (O. ×citriodorum Vis. ‘Lime’), and lemon basil (O. basilicum L. ‘Sweet Dani’) were chosen. Seeds were sown into 162-count sheets of phenolic foam propagation cubes, placed in a growth chamber with a target air temperature of 24 °C, and irrigated with deionized water or a nutrient solution. Two weeks after sowing seeds, seedlings were transplanted into nutrient film technique (NFT) systems in a greenhouse with high (15.0 mol∙m⁻²∙d⁻¹) or low (6.9 mol∙m⁻²∙d⁻¹) DLI with a mean air temperature of 21.7 °C. The NFT systems contained five different nutrient solution concentrations (0.5, 1.0, 2.0, 3.0, or 4.0 mS∙m⁻¹) comprised of 16N−1.8P−14.3K complete fertilizer. Nutrient solutions were adjusted daily to maintain target ECs using a stock solution and a pH of 6.0 with buffers. Three weeks after transplanting, height, node number, branch number, and fresh mass were recorded. For plants grown under either a low or high DLI, there was no difference in fresh mass between plants grown in different nutrient solution concentrations. For example, sweet basil grown under a high DLI in a nutrient solution of 0.5 mS∙cm⁻¹ had a mass of 27.4 g compared to 27.3 g for plants grown in 4.0 mS∙cm⁻¹ nutrient solution. Alternatively, there were differences between plants grown under a low and high DLI. Fresh mass of sweet basil plants grown in a 1.0 mS∙cm⁻¹ nutrient solution under a low DLI was 22.0 g less than plants grown under high DLI while plants were 3.9 cm shorter. Under low or high DLIs, the concentration of nutrient solution has no effect on fresh mass. Therefore selection of nutrient solution concentrations should be based on meeting required tissue concentrations while minimizing the amount of fertilizer used.