Abstract

The cannabis plant has been cultivated for decades, although the plant is considered an addictive substance in many countries around the world, both as a hemp and medicinal variety. Previously, commonly grown plants were classified as industrial hemp, i.e. cannabis with a THC content of less than 1 %. However, in recent years, it has been possible to commercially grow so-called cannabis for medical use, i.e. cannabis that can contain more than 20 % of this cannabinoid.

In the Czech Republic, cannabis for medical use can only be grown in climatecontrolled brick buildings without access to daylight, which means that growers must grow plants differently than in the fields and must control all inputs and parameters, which requires a considerable degree of understanding of the growing system.

One of the most discussed parameters controlled by growers is light, including its quality and quantity, as well as fertilisers. Fertilisers (their different concentrations) and light (its different intensity) were the subject of this thesis.

In this experiment, cannabis plants were grown in a controlled environment, where they were cultivated for twelve weeks overall. These plants were subjected to two regimes of fertilisers, R1 and R2.

Fertiliser regime R1 was applied for the whole growing cycle (vegetation and flowering phase) with parameters N-NO3 − 131.26 mg L⁻¹; N-NH4 + 6.23 mg L⁻¹; P2O5 30.85 mg L⁻¹; K2O 112.46 mg L⁻¹; CaO 147.90 mg L⁻¹; MgO 45.72 mg L⁻¹; SO4 2- 33.79 mg L⁻¹. Fertiliser regime R2 was divided into the vegetation phase and the flowering phase. In the vegettation phase (first four weeks), the fertiliser rate was applied at N-NO3 − 164.99 mg L⁻¹; N-NH4 + 5.28 mg L⁻¹; P2O5 65.87 mg L⁻¹; K2O 228.27 mg L⁻¹; CaO 125.42 mg L⁻¹; MgO 78.93 mg L⁻¹; SO4 2- 50.16 mg L⁻¹. In the flowering phase (from fifth week to harvest), N-NO3 − 98.87 mg L⁻¹; N-NH4 + 5.82 mg L⁻¹; P2O5 262.77 mg L⁻¹; K2O 248.36 mg L⁻¹; CaO 138.31 mg L⁻¹; MgO 85.33 mg L⁻¹; SO4 2- 11.20 mg L⁻¹.

The intensity of the light was divided into two groups for both the growth and flowering phases, where the S1 group for the growth phase was set to 300 μmol m⁻² s⁻¹, the S2 group for the growth phase to 500 μmol m⁻² s⁻¹ and for the flowering phase, the S1 group to 900 μmol m⁻² s⁻¹ and the S2 group to 1300 μmol m⁻² s⁻¹. The statistical analysis of ANOVA did not confirm the effect of fertilisers on inflorescence yield or cannabinoid content in the monitored plants. On the other hand, the light intensity had a significant effect on both the yield of inflorescences and the content of the monitored secondary metabolites, THC, CBD, CBG and CBC, with the content of these substances increasing by up to 43 %.

The results confirm that light intensity is a key factor influencing both quantitative and qualitative yield of plants, while the composition of fertiliser spreads does not have such a high effect on these metrics.

The experiment also included a life cycle analysis (LCA) to assess the environmental impacts of growing cannabis in a controlled environment for groups. R1.S1., R1.S2., R2.S1. and R2.S2., where it was confirmed that the main factors affecting the environmental burden are electricity consumption and fertiliser application, with electricity having a dominant impact on the carbon footprint. However, the life cycle analysis paradoxically confirmed that higher light intensity has a lower environmental impact than lower light intensity, as it brings a higher yield of dry inflorescences and thus a lower burden per unit of production.