S08 - Session O3 - Keynote: Technological overview of tip-burn management in vertical farming conditions

Authors: Chieri Kubota *, Gio Papio, John Ertle

Tip-burn is an environmental nutrient disorder caused by calcium (Ca) deficiency in the plant. As Ca uptake is driven by mass flow, the incidence of tip-burn is often understood in plant-water relations affected by many environmental factors. Plant transpiration, root pressure, and resulting xylem pressure take an important role determining the Ca transport to the growing shoot tip. However, plant-water relations can only partially explain the incidence of tip-burn, as tip-burn appears when mass-flow-driven Ca does not meet the Ca demand for plant growth. Therefore, susceptible plants would develop tip-burn under conditions that enhance growth rate (e.g., high light and high CO 2 concentration) but limit transpiration (e.g., low vapor pressure deficit (VPD) and limited air circulation). These conditions are commonly seen among indoor vertical farms. Among several mitigation measures, use of downward airflow fans over crops is widely practiced in greenhouse hydroponic lettuce production. However, installation of fans to create uniform downward airflow is rather challenging in narrow headspaces of indoor vertical farms. Furthermore, the sole source electrical lighting lacks thermal near-infrared radiation (800-3000 nm) and does not drive plant transpiration as much as solar radiation, when compared at the same photosynthetic photon flux density. Therefore, many growers select shorter production cycles (e.g., for lettuce, 3-5 weeks after seeding instead of 6 weeks or longer) to avoid tip-burn risk at final stage of production cycle, during which plant biomass (i.e., yield) increases rapidly. Other mitigation measures include high night-time humidity ( < 0.1 kPa VPD) and foliar Ca spray. Therefore, this practice of short cycle production of leafy greens seems to limit the profitability of indoor vertical farms. At the Ohio State University, we are developing new strategies to assess and manage the risks of lettuce tip burn. Our strategies combine direct measurements of evaporation using a small dish evaporator to quantify the potential transpiration rate and a reference crop growth model considering plant light interception, CO 2 concentration and temperature. While predicting tip-burn accurately continues to be a challenge, environmental risks can be better understood using our sensing/modelling-based approach.