2017 ASHS Annual Conference

Recirculating nutrient solutions for hydroponic production systems are frequently adjusted to maintain target pH and electrical conductivity (EC) values. Greenhouse hydroponic crop production occurs year-round, and the photosynthetic daily light integral (DLI) varies throughout and across seasons and greenhouse facilities. Crop culture, such as nutrient solution EC, may need to be adjusted with the changing light environment. The objectives of our research were to quantify the impact of DLI and nutrient solution EC on the growth and tissue nutrient concentration of cilantro (Coriandrum sativum L.), dill (Anethum graveolens L.), and parsley (Petroselinum crispum (Mill.) Fuss.). Seeds of ‘Santo’ cilantro, ‘Fernleaf’ dill, and ‘Giant of Italy’ parsley were sown in 162-cell sheets of phenolic foam propagation cubes and grown in an environmental growth chamber. Three weeks after sowing seeds, seedlings were placed into NFT systems in greenhouses with either a low (5.5–7.5 mol∙m^–2∙d^–1) or high (17.9–19.3 mol∙m^–2∙d^–1) DLI and an air temperature of 21.4–22.3 °C across DLIs and replications. The NFT systems contained nutrient solutions comprised of deionized water supplemented with a complete, balanced water-soluble fertilizer (16N–2.2P–14.3K) maintained at 0.5, 1.0, 2.0, 3.0, or 4.0 dS∙m^–1. Fresh and dry mass were affected by DLI but not EC. Compared to plants grown under a low DLI, fresh mass increased by 21.0, 17.1, or 13.3 g for cilantro, dill, and parsley, respectively, under a high DLI. Dry mass followed a similar trend as fresh mass. Tissue nutrient concentrations were affected differently by DLI and EC across species. Nitrogen concentration of cilantro, dill, and parsley shoots were unaffected by DLI or EC and were 5.5%, 6.1%, and 4.7%, respectively. Alternatively, while P concentration for parsley increased as DLI increased, K decreased. while tissue K concentration for dill grown under low DLIs increased as EC increased from 0.5 to ≥ 1.0 dS∙m^–1, it was unaffected by EC under high a high DLI. There were few effects of DLI or EC on micronutrient tissue concentrations. Nearly all tissue nutrient concentrations were within or above recommended ranges for each species across ECs and DLI among species. The results of this study illustrate that DLI, not nutrient solution EC, affects growth. Furthermore, as long as nutrient solutions ECs are frequently supplemented or amended with fertilizer, low ECs may be used under low and high DLIs and produce healthy plants with adequate tissue nutrient concentrations.