Identifying Plant Nutrient Uptake under Different Concentrations of N

Martine Dorais from Laval University presented her work on plant nutrient uptake in cannabis at the 2022 Canadian Greenhouse Conference. A summary of her presentation can be found below:

One of the first thing she presents is a look at the difference in water use for two different rates of N supplementation. While there is an obvious spike of water uptake in week two for the plants receiving 250 ppm N, the differences in water use between the two treatments quickly levels out over time. Depending on your fertigation plan, more or less water may be necessary for your crop in those first few weeks of growth. 

Next up, her team decides to explore how different rates of N are going to impact the uptake of other key nutrients. Below, we can see the response of K uptake, and Ca uptake as a response to the amount of N in the system. Both nutrients see a significant spike in uptake at week two in the 250 mg/L N treatment, however the shape of the uptake curve is not necessarily reflected in the 150 mg/L N treatment. The different uptake patterns is an interesting trend to note here, which has implications for fertilizer recipe ratios over time depending on what level of N you are feeding. 

The next analysis looks at the uptake rate of P-PO4 and Mg. Right off the bat, we see that the nutrient uptake patterns here are quite different to what was observed above. For P-PO4, instead of seeing a spike at 2 weeks, the uptake spike happens around week 5 of growth. Mg sees a peak at week 2, but again at week 6, with similar patterns across the two treatments of N. In the case of both of these nutrients, I think that noticing the scale for these graphs (significantly lower uptake rate compared to that of K and Ca) as well as her note that the amount of N supplemented did not have a significant impact on nutrient uptake. From a recipe formulation standpoint, levels of Mg and P-PO4 can stay relatively constant when increasing/decreasing the amount of N being fed to the crop. 

How does this translate to our final product?

It's becoming widely accepted that different strains of cannabis do not behave the same way, not just in a the sense that they produce different plant architectures, but in their responses to different environmental conditions as well. The results presented below are a perfect example of that. White Shark saw a 29% increase in dry inflorescence weight per plant as a result of the higher N feed. Critical Orange Punch, however, did not differ significantly in the dry weights produced.

Take this one step further, Martine's team wanted to see the impact of the two different rates of N on the % of cannabinoid production, and the study yielded some interesting findings: 

Cannabinoids (%)	N-NO3 Concentration
	250 ppm	150 ppm
THCA	17.98	18.47
Delta9-THC	0.31a	0.14b
CBDA	0.28	0.02
CBD	0	0
CBDV	0	0.04
CBN	0.31	0.29
CBG	0.04	0.06
CBGA	0.35	0.57
CBC	0	0.91
Total THC	16.13b	17.66a
Total CBD	0.25	0.03

While Delta9-THC was significantly higher at the 250 ppm N rate compared to the 150 ppm rate, the total THC levels show that the lower supplemented N rate of 150 ppm actually yielded a higher percentage of cannabinoids compared to the higher rate of N. In this particular case, more N was not necessarily conducive to bigger and better quality product. Studies like this are crucial for being able to target nutrient supplementation to important time stamps, as well as begin to understand exactly what goes into growing the best possible flower. 

Martine Dorais' team produced a lot more results than what I have summarized here, and I encourage you to explore the entire presentation to see the full scope of work that was conducted. You can find the entire slide deck here.

Posted by: Talia Plaskett