S06 - Session P8 - Response of drug-type Cannabis sativa L. to P and K concentrations for plants grown in a deep-water system

Authors: Camille Leblanc, Thi Thuy An Nguyen, Annie Brégard, Martine Dorais *

Drug-type Cannabis sativa L. is a fast-growing industry following its legalization in Canada. However, the lack of scientific agronomic knowledge about cannabis cultivation is one of the main challenges for the growers. Most studies on the mineral nutrition of cannabis were realized on hemp and N fertilization.The number of studies on P and K conducted with drug-type cannabis is still limited although they are two important macronutrients. To better understand the impact of these two nutrients on plant development, productivity, and quality, we have studied five P (25, 50, 100, 150, 200 mg L -1 ) and two K (175 and 250 mg L -1 ) concentrations during the flowering phase of one genotype plants cultivated in a deep-water growing system. The aim of this study was to identify the optimal P and K concentrations that promote plant development, flower yield and the potency in cannabinoids and terpenes. The experimental design was a randomized complete block with four replicates located in a greenhouse at Laval University. Our results showed that P and K concentrations did not have a significant impact on plant growth parameters, flower yield and potency. Based on K leaf content we observed that C. sativa had a luxury consumption of K when the concentration was 250 ppm. Ca leaf content was negatively correlated with K concentrations of the nutrient solution. An interaction P x K was observed for the leaf Mg content resulting in a decreased in Mg as P and K increase. Overall, our results suggest that hydroponic cannabis growers do not need to use a concentration above 25 mg L -1 for P and 175 mg L -1 for K as those levels were sufficient for an optimal plant development and yield. However, these levels may vary according to the genotype and the light growing condition, as our experiment was conducted with only one genotype and under relatively low light conditions.