Influence of water shortage and N:P ratio on growth and seed chemical components of hemp ( Cannabis sativa L.)

Seeds of industrial hemp have high nutritional and healthcare value, which can be further improved by proper cultivation methods. Biochemical properties of hemp seeds that are beneficial for human use can be modulated through variation of the molar ratio between the inorganic nitrogen and phosphorus supplied with the nutrient medium, as well as by creating a moderate water deficit during controlled irrigation. The aim of this study was to investigate the influence of two N:P ratios (i.e. 8 mM nitrogen as nitrate to 2 mM phosphorus as phosphate, and 3 mM nitrogen to 6 mM phosphorus), combined with two water supply regimes (sufficient and insufficient) on vegetative growth parameters, seed production, seed oil, protein, vitamin E, iron, zinc and manganese content of two industrial hemp cultivars ('Jubileu' and 'Zenit'). The experiments were performed in a greenhouse, under controlled conditions. Even if plants receiving a lower N:P ratio and lower water supply had a decreased growth index and the shoot fresh weight was smaller, no statistically significant difference could be registered in the seed production of the different experimental variants. The oil content of seeds could be increased by a lower N:P ratio and by water deficit, while seed protein content was higher upon a higher N:P ratio and upon water shortage, for both cultivars. The highest vitamin E content of hemp seed oil was found when plants were subjected to the combined influence of lowered N:P ratio and water insufficiency. The iron content of seeds showed no changes between the different experimental variants. In seeds of the 'Jubileu' variety the zinc content was increased by water shortage when the N:P ratio was lower, while the highest manganese content was measured when plants received sufficient water and lowered N:P ratio. As for the 'Zenit' variety, the highest zinc and manganese content of seeds was obtained when plants received through the nutrient solution 8 mM nitrate and 2 mM phosphate (i.e. the N:P ratio was 4:1). The findings may contribute to optimization of hemp cultivation, in a cost-effective and environmental-friendly approach, for the purpose of production of higher quality seeds for human and animal consumption, as well as for the cosmetic industry.