The use of vegetal tissue multi-element content as an indicator of soil or substrate type employed to cultivate Cannabis sativa L. (marijuana)

Abstract

Brazil plays a significant role in the cultivation and production of marijuana. The Brazilian Federal Police (BFP) statistics demonstrate an increase in the apprehension of ready-to-use marijuana and cannabis seeds, indicating that indoor cultivation is becoming more common. The present research aimed to test the use of multi-element content in vegetal tissue samples as an indicator of soil or substrate cultivation and, more specifically, to determine whether it is possible to differentiate cannabis plants grown in different soil types. To do so, seeds seized by the Brazilian postal authorities were germinated and cultivated indoor under controlled conditions by the BFP. Then, cannabis plants were grown in two soil (Ultisol and Chernosol) and one substrate comprising organic soil, earthworm humus, and sand. In total, forty-nine (49) cannabis plant samples were analyzed. After digestion, 19 elements were analyzed by inductively-coupled plasma optical emission spectrometry (ICP-OES), and the data were compared by the Kruskal-Wallis H test followed by a multiple discriminant analysis (MDA) to classify samples cultivated with different types of soil and substrate. The model correctly classified 100% of samples in their respective group with an uncertainty of ≤ 2.2%. The MDA demonstrated that manganese, nickel, calcium, magnesium, barium, copper, and zinc were the best set of elements to discriminate Cannabis plants grown in different soil types or substrates. Therefore, the multi-element content of the plant material combined with a robust statistical tool can be applied as an indicator of the type of soil or substrate used to cultivate marijuana.