Phosphorus fertilisation differentially influences growth, morpho-physiological adaptations and nutrient uptake of industrial hemp (Cannabis sativa L.)

Abstract Background and Aims Phosphorus (P) is a restricting nutrient for crop productivity worldwide. P deficiency can lead to stunted growth and development, eventually affecting crop yield. But less is documented about the impact of P fertility on industrial hemp ( Cannabis sativa L.) production in the low-P soils of south-western Australia. We aimed to investigate the effect of P rates on growth, physiology, rhizosphere carboxylate exudation, nutrient uptake and P-use efficiency in hemp. Methods The study was conducted in a randomised complete block design with four P rates (0, 40, 80 and 120 mg P kg –1 dry soil) and three hemp varieties (Morpeth, Han FNQ and Fedora 17). Plants were grown and raised in a controlled-environment phytotron until harvested 35 days after sowing at vegetative growth stage (3 rd to n th leaf pair). Results Our results revealed a strong influence of treatment (P rate) on hemp growth, physiology, biomass, nutrient uptake and P-use efficiency compared to variety and the variety × treatment interaction. Hemp roots predominantly released citrate in P-deficient conditions and gradually shifted to malate exudation with increasing P supply. The N:P ratio, leaf chlorophyll, and gas exchange data coupled with shoot and root length data suggest that Morpeth and Fedora 17 differ in morpho-physiological adaptations for optimum photosynthesis and growth, with high leaf chlorophyll and coarse root length achieved by Morpeth and high intercellular CO 2 concentration and shoot length by Fedora 17. Conclusions Morpeth and Fedora 17 had high shoot biomass, root length, root surface area and agronomic P-use and P-utilisation efficiencies in response to increasing soil P, while Han FNQ had moderate shoot yield, root growth, high citrate exudation, tissue P concentration and P-uptake efficiency.