Effect of Potassium (K) Supply on Cannabinoids, Terpenoids and Plant Function in Medical Cannabis

We have demonstrated in previous studies that the essential macro-nutrients nitrogen (N) and phosporous (P) have profound effects on the production of cannabinoids and terpenoids in the cannabis plant. The present study was undertaken to evaluate the hypothesis that potassium (K) supply, which is known to substantially affect plant development and function, affects the secondary metabolism of the cannabis plant. Two cultivars of medical cannabis were grown in controlled environment conditions, under five levels of K supply: 15, 60, 100, 175, and 240 mg L−1 K. The results revealed that the development and function of plants that received the low K supply of 15 mg L−1 K were impaired, as the plants suffered from visual chlorosis, and the inflorescence yield was reduced in both cultivars. Plants that received higher K inputs in the range of −175 mg L−1 K demonstrated optimal plant function and high yield, and one cultivar demonstrated over-supply symptoms under the high K level of 240 mg L−1. The concentrations of most cannabinoids and terpenoids declined with the elevation of K supply, thus supporting the hypothesis. As secondary metabolite concentrations decreased with the increase in K supply, and higher K levels had no positive effects, 60 mg L−1 K is the suggested application level to maintain high function and yield combined with high secondary metabolism.