Date of Graduation
5-2025
Document Type
Thesis
Degree Name
Master of Science in Horticulture (MS)
Degree Level
Graduate
Department
Horticulture
Advisor/Mentor
Dickson, Ryan W.
Committee Member
Bertucci, Matthew B.
Second Committee Member
Roberts, Trenton L.
Third Committee Member
Fisher, Paul
Keywords
Fertilizer; Greenhouse; Herbs; Hydroponics; Leafy Greens
Abstract
Hydroponic systems recirculate nutrient solution to reduce the amount of water used in leafy green production. However, the rootzone of the nutrient solution is complex and influenced by interacting factors such as plant uptake demand, irrigation water quality, supplied fertilizer salts and nutrient concentrations, environmental conditions, and injection of mineral acids/bases to control solution pH. A common strategy for managing nutrients in commercial production is to select a hydroponic solution formulation (i.e. recipe) to supply and maintain a target pH and electrical conductivity (EC) in the recirculating solution over time by automatic injection of mineral acids/bases and concentrated fertilizer stock solutions. During nutrient replenishment of the recirculated solution, nutrients are resupplied at the same ratios at which they are supplied in the initial solution. Often with this approach, the resupply of nutrients is not balanced with plant uptake demand, resulting in root zone nutrient imbalances which can cause yield reductions and motivate growers to dump and replace solution. The objective was to develop a novel strategy for managing nutrients in recirculating solutions designed to supply and maintain optimal macronutrient concentrations and solution pH with basil (Ocimum basilicum) and lettuce (Lactuca sativa) as model crops. The strategy consisted of custom formulating species-specific initial and replenishment solutions formulated using a combination of data on plant tissue nutrient concentrations, previously published nutrient management guidelines and peer-reviewed research, and common grower tools and experience. The custom initial solution for each species was intended to supply macronutrient concentrations at near optimal ratios whereas the custom replenishment solution was intended to replace the nutrients taken up and maintain the concentrations/ratios in the initial solution. The custom strategy was evaluated with basil and lettuce grown for 56 d in deep water culture (DWC) systems and compared to a control strategy consisting of a common 2-part fertilizer formulation for both the initial and replenishment solution. Overall, the custom strategies for basil and lettuce resulted in macronutrients remaining near the initial concentrations supplied whereas the control strategy resulted in macronutrients, particularly calcium and sulfur, which deviated substantially from the initial concentrations. A separate experiment evaluated the custom nutrient management strategy with basil grown in hydroponic nutrient film technique (NFT) systems, where nutrient solutions were formulated using two sources of irrigation water differing in soluble salts and alkalinity. Overall, solution macronutrient concentrations remained more stable over time with the custom strategy compared to the control strategy for both irrigation water qualities. Yield was greatest for basil grown in hydroponic solutions formulated using the high alkalinity irrigation water as a result of the additional nitrogen (N) supplied by nitric acid (HNO3) injection used to neutralize the water alkalinity and adjust solution pH.
Citation
Tebow, J. B. (2025). Developing Custom Fertilizer Strategies Recirculating Hydroponic Systems. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/5640
