Potassium and micronutrient fertilizer addition in a mock aquaponic system for drug-type cannabis sativa l. Cultivation

Abstract

Cultivating drug-type Cannabis sativa L. with aquaponics could reduce mineral fertilizer use; however, its nutrient solution is often unbalanced and low in K+ and micronutrients. It is unknown if a K+ fertilizer, a micronutrient fertilizer, or both, would improve C. sativa production in aquaponic solution, as optimal K+ and micronutrient concentrations in the root zone for C. sativa during the flowering stage have not been investigated. To determine the effects of adding a K+ fertilizer and a micronutrient fertilizer to aquaponic solution for C. sativa production, we grew drug-type C. sativa in five aquaponic based solutions: aquaponic solution (con-trol plants) (15 mg·L−1 K+ ); aquaponic solution with added micronutrients (Fe3+, Cu2+, Mn2+, B3+, Mo3+, and Zn2+ ); and aquaponic solution with added micronutrients and three K+ concentrations (75, 113, and 150 mg·L−1 ) during the flowering stage. To evaluate the impact of additional K+ and micronutrients on C. sativa production, we measured growth (vegetative parameters and weight), physiology (leaf gas exchange), leaf nutrition content, and yield (inflorescence weight). Adding the K+ fertilizer at 75 and 113 mg·L−1 with micronutrients to aquaponic solution increased harvest index (marketable inflorescence to shoot weight) by 16% and 22% compared with the control, respectively. Cannabis sativa dry apical inflorescence and total inflorescence yield also increased linearly with increasing K+ concentration. Alternatively, plants grown in the control (suboptimal K+ and micronutrient conditions) had no difference in growth or measured physiological parameters compared with plants with supplemented nutrients. Our study suggests that aquaponic solution mitigates low K+ concentrations from causing deficiency.