New study on P accumulation in medical cannabis

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AmWeedwolf

AmWeedwolf

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An exciting new study has been published by Frontiers in Plant Science on the effect of phosphorus supply on medical cannabis flower yield, cannabinoid content, and plant morphology.

Before I get into the results, I want to note that P (phosphorus) concentrations are different from phosphate (P2O5) concentrations listed as NPK numbers on fertilizer labels. To determine phosphate levels multiply P by 2.29. For example, 30 ppm P = 68.7 ppm P2O5

Its main findings were:
  • P levels between 30-90 ppm were within the optimal range for plant development and function sufficient for achieving maximum yield.
  • P levels of 30 ppm achieved maximum flower yields in the high THC/low CBD strain 'Royal Medic' while p levels of 90 ppm achieved maximum flower yield in the balanced THC/CBD strain 'Desert Queen'. However, the opposite was found for total cannabinoid yield per plant; 30 ppm P achieved max cannabinoid yields for the balanced THC/CBD strain, while 90 ppm P was needed to achieve maximum cannabinoid yield in the high THC/low CBD strain.
  • P supply above 5 ppm lowered cannabinoid levels by up to 25% and were highest <30 ppm for both strains
Yield p

Total cannabinoids p

Cannabinoids p


My takeaway is that these results appear to be somewhat preliminary and are genotype-specific and relevant only to hydroponic systems under artificial lights with highly controlled environmental conditions. Additional research is needed to see if the observed effects ring true for other (similar) strains in this system. Additional research is also needed to explore the effects of P availability in systems with less uniform (organic, living soil) and/or sub-optimal (greenhouse/outdoor) environmental conditions, especially regarding the interaction of P availability and mycorrhizae colonization and the resistance to fungal pathogens this confers.

But it's a very interesting new data point on the debate about Phosphorus requirements in Cannabis cultivation!
 
Aqua Man

Aqua Man

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Interesting yes. 2020 study found some conflicting info.

5. Conclusions These results indicate that C. sativa has different fertility requirements based on the life stage and the end goal of production. For example, if a grower is producing mother stock plants for vegetatively propagated cuttings, plants will remain vegetative throughout their lifecycle. Thus, a concentration of 11.25 mg·L−1 P or greater may be adequate for this operation. If C. sativa plants are to be grown for the florescence and/or cannabinoids or terpenes either for the fresh flower market or a distillate market, a P concentration above 11.25 mg·L−1 is preferred. While a P concentration of 22.5 mg·L−1 resulted in the greatest bud fresh weight when compared to the lowest two concentrations, it did not result in any greater increase in the active or acid cannabinoid pools. Additionally, higher P rates above 22.5 mg·L−1 did result in greater lateral production and consequently more nodes to produce the economic portion (floral material). Thus, a follow-up study should be completed to see if the increase in lateral nodes and floral material would result in a greater whole plant yield in floral material, despite the higher concentration of P resources not resulting in greater cannabinoid production in said flowers. Thus, for production in a cannabinoid or distillate market, a P fertility concentration of 11.25 mg·L−1 would be adequate, while for fresh market production, a P fertility concentration may be greater (22.5 mg·L−1) to account for more visually appealing floral material.
Additionally, these results indicate that the luxury consumption level for C. sativa regarding plant growth metrics and leaf tissue accumulation was not reached, given that no leveling off or plateauing of leaf tissue P was observed. This may indicate that C. sativa requires higher levels of P fertility to reach the uppermost limit of resource accumulation in the leaf tissue. Higher levels of P fertility concentrations should be explored to elucidate the uppermost levels of P resources the plant can acquire in the leaf tissue. Additional screening should be completed with other cultivars to quantify different P fertility needs more accurately for other types of C. sativa, given that a wide variety of plant architectures exists within C. sativa (Figure 5). Furthermore, the sampling of different plant parts (petioles, stems, roots etc.) for mineral nutrient concentration overtime would help illuminate the accumulation and reallocation of mineral resources within C. sativa over its life stages
 
Aqua Man

Aqua Man

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I mean not totally conflicting and leaves room to expand on so looking further at the levels tested it may just be accurate.

It does definitely jump out at me how in both sativa appear to benefit from a high concentration. With most genetics being indica leaning or fairly even these days due to yields and flowering time. I'd say most likely don't need more than 30ppm however making sure that it's in available form is I think where many of us lack
 

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