Date of Award:

5-2024

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Committee Chair(s)

Bruce Bugbee

Committee

Bruce Bugbee

Committee

Youping Sun

Committee

Lance Stott

Abstract

Cannabis has been cultivated for millennia as a multipurpose crop for food, fiber, and medicine. Secondary metabolites called cannabinoids, including cannabidiol (CBD) and the psychoactive Δ-9 tetrahydrocannabinol (Δ-9 THC), are responsible for the medicinal properties of cannabis. The intoxicating nature of THC resulted in legislation prohibiting the possession and production of cannabis within the United States during the 20th century. As a result, research programs on cannabis production were halted at most institutions. In recent years, cannabis production has become widespread within the US as a result of increasing legalization. However, modern cannabis production nutrient management programs often include holdover practices from prohibition era clandestine production which are often based on anecdotal evidence. Practices thought to increase yield and cannabinoid production include excessive fertilizer application and preharvest fertilizer deprivation (flushing). However, increasing commercial production have increased scrutiny on the environmental impact of cannabis production. This thesis encompasses the results of two studies pertaining to nutrient management of medical cannabis in controlled environments. The first study investigated the effects of nutrient solution concentration and phosphorus (P) supply on plant development, flower yield, cannabinoid production, nutrient use efficiency and nutrient partitioning in closed system, deepwater hydroponics. The second study examines the effects of preharvest nutrient deprivation, a practice colloquially known as flushing, on yield, cannabinoid production and nutrient partitioning of medical cannabis. The results from the first study indicated that excessive nutrient supply did not increase flower or cannabinoid yield. Moreover, nutrient concentrations within the recirculating solution and tissue increased with increasing nutrient supply. Applied nutrients that are not utilized by the plants can enter the environment as a pollutant. In the second study preharvest nutrient deprivation did not increase flower quality or total cannabinoid yield. Moreover, a common reason used to advocate flushing is the reduction of flower tissue nitrogen (N) content, which is thought to negatively impact sensory qualities during smoking. In the leaves visual symptoms consistent with nutrient deficiency were evident within one week of initiating flushing treatments. Nutrient analysis of leaf and flower tissue showed decreasing leaf concentrations of N, but flower concentrations were unchanged.

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