"Cannabis is a commodity with high nutrient demands due to prolific growth under optimized environmental conditions. Since nutrient deficiencies can reduce yield and quality, cultivators need tools to rapidly detect and evaluate deficiency symptoms so corrective actions can be taken quickly to minimize losses." Therefore, the University of Guelph has recently conducted a study to identify deficiency symptoms. The trial deliberately induced nutrient deficiency symptoms by withholding individual nutrient elements from respective treatment solutions while maintaining sufficient levels of all other nutrient elements. Plants were monitored daily, and the development of visual deficiency symptoms were recorded. "Overall, deficiencies of individual nutrients can substantially reduce vegetative growth and inflorescence yield, although only minor effects were observed in secondary metabolite composition."
Impact on yield
In addition to the thorough descriptions of the development of visual deficiency symptoms, the study demonstrates the relative severity that different nutrient deficiencies can have on yield and quality, including secondary metabolite composition. "It has been well established that suboptimal supply of major nutrient elements during the flowering stage can substantially reduce cannabis vegetative growth and inflorescence biomass." According to the results of the study, the vegetative and inflorescence biomass in -N and -P treatments were almost three times lower, and between 30% to 50% lower in the -K, -Ca, -Mg, and -S treatments vs. the control treatment. Only the -Fe and -Mn treatment plants had no reductions in aboveground biomass, compared to the control treatment, none of which showed major signs of nutrient deficiency at harvest. The N- and K-deficient plants had the lowest root dry weights, while the P-deficient plants had the highest root dry weights. "There were also no nutrient deficiency treatment effects on harvest index, which was unexpected since deficiencies in less mobile nutrients (e.g., Ca and S) should have proportionally greater effects on the development of the relatively younger inflorescence tissues. Furthermore, the apportioning of individual nutrients between vegetative and inflorescence cannabis tissues have been shown to be quite variable, there may be complex synergistic effects amongst individual nutrient elements, and in some cases, nutrient supply appears to affect harvest index."
"Small effects on cannabinoid concentrations"
The 'Gelato 29' cannabis cultivar is strongly THC-dominant, with total THC comprising over 96% of the total cannabinoid concentrations (i.e., in the control treatment). "Compared to the nutrient treatment effects on biomass, there were relatively small treatment effects on cannabinoid concentrations, predominantly in the minor cannabinoids. Of particular note were the differences between the plants in the -K vs. the -Ca treatments. Generally, the -K treatment plants had amongst the highest concentrations of all measured cannabinoids, whereas the -Ca treatment plants had the lowest concentrations of some individual cannabinoids, including CBDA, CBGA, and THCA, which were each between 35% and 45% lower than in the -K treatment."
"Higher nutrient supply levels have sometimes been associated with decreases in some cannabinoid concentrations, but these were generally offset by relatively much greater increases in inflorescence yield (i.e., the so-called "dilution effect"). Therefore, with inflorescence yield being the dominant economic driver in cannabis cultivation, any small increases in cannabinoid concentrations from growing plants in low nutrient conditions are unlikely to be commercially relevant," the researchers add. "Within moderate levels of nutrient supply, nutrient concentrations may not substantially affect secondary metabolite composition but extreme nutrient supply levels (i.e., too low or too high) can. Whether nutrient stress can be used as a production tool to manipulate cannabis quality requires further investigation."
To read the complete study, go to www.mpdi.com