Date of Graduation

12-2021

Document Type

Thesis

Degree Name

Master of Science in Horticulture (MS)

Degree Level

Graduate

Department

Horticulture

Advisor

Ryan W. Dickson

Committee Member

Trenton L. Roberts

Second Committee Member

Matthew Bertucci

Keywords

Controlled environment, Designed solutions, Hydroponics, Nutrient management, Nutrient solution

Abstract

Nutrient management in recirculating hydroponic systems requires the periodic replenishment of water and nutrients to the nutrient solution reservoir. Common nutrient management strategies, such as replenishing the reservoir with fresh solution and maintaining a constant solution electrical conductivity (EC), can lead to ion accumulation and nutrient imbalances since nutrients are taken up by roots and depleted from solution at different rates. To avoid nutritional disorders, commercial growers typically dump and replace the hydroponic solution periodically, which is wasteful and has an economic cost. A potential alternative is to specially formulate the nutrient replenishment solution to balance the supply of nutrients with the uptake of nutrients into plant tissues. As a result, nutrients would be consistently replaced in solution at a rate similar to the uptake by plant roots. A range of published nutrient solution formulations for hydroponic leafy greens crops were reviewed and shown to vary considerably in nutrient concentrations, many of which would be expected to oversupply certain nutrients, particularly calcium, magnesium, and sulfur. A study was conducted to quantify nutrient uptake and water use efficiency (WUE) by arugula (Eruca sativa L.) and basil (Ocimum basilicum L.) and determine if the strategy for replenishing nutrients impacted plant growth and nutrient uptake. A second study evaluated the potential to design a species-specific replenishment solution for arugula and basil to minimize the accumulation of ions in solution over time. Overall, arugula and basil differed in plant growth, uptake of individual nutrients, and transpiration, but were similar in WUE. Nutrient replenishment strategy had minimal to no impacts on plant growth, nutrient uptake, or WUE. Similarly, species-specific replenishment solutions formulated for arugula and basil had minimal effects on plant growth, nutrient uptake into plant tissues, or WUE when compared to nutrient replenishment with a standard hydroponic solution used commercially. Species-specific replenishment solutions also decreased the accumulation of nutrient ions, particularly calcium, magnesium, and sulfate, compared to a standard hydroponic replenishment solution. For both arugula and basil, solution EC increased when nutrients were replenished with the commercial standard solution, but remained more stable when nutrients were replaced using the species-specific replenishment solutions. Species-specific replenishment solutions may be a strategy for growers to prevent salt accumulation and ion imbalances in recirculating hydroponic systems, minimizing the risk of nutritional disorders and the need to dump and replace solution. Since species-specific replenishment strategies reduced changes in solution EC over time, this approach would improve the practice of managing nutrient supply by maintaining a target EC level. Growers can develop their own species-specific replenishment solutions by monitoring plant uptake of nutrients, growth and yield, and water use during production.

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