This study was undertaken to identify factors that could predict the average yield
of usable biomass under specific growing conditions. The study shows that planting
density is a significant factor affecting the shape of plant canopy, which in turn
affects the total plant yield. Cannabis crop was cultivated under five different planting
densities i.e. 9, 18, 36, 72 and 81 square feet per plant (sq.ft/plant). At the higher
planting density (9–18 sq.ft/plant), the horizontal growth rate was decreased which
resulted in tall plants and narrow plant canopies, whereas, plants grown under lower
planting density (36–92 sq.ft/plant) had larger branching structures coupled with
increased available sunlight, soil nutrients and water which resulted in significantly
greater biomass yield.
Accurate estimate of plant yield can be predicted based on the plant's fresh weight
or based on the measurement of the diameter of the plant at the broadest point in
the canopy. The fresh weight at the time of harvest multiplied by the number 0.1437
would result in an estimate of dry weight of useable plant material. That is, on average,
14.37% of the total wet (fresh) weight of the plant would be dry useable biomass.
A correlation was also developed between the diameter of a plant's canopy and the
dry weight of the plant, resulting in an empirical formula to calculate the plant's
total dry weight {dry weight=–3.76786 + (0.06666×diameter in cm2)}. The percent usable biomass is then found considering that 34% of the total dry
weight of non-sinsemilla plants and 58% of sinsemilla plants is usable biomass. Acknowledgements: The authors acknowledge the support of the United States Drug Enforcement Administration
(DEA) and the National Institute on Drug Abuse (NIDA), National Institute of Health
(NIH), Department of Health and Human Services, USA.
