The scientific secret behind hemp's efficiency

New European research initiative sheds light on what makes hemp such a productive crop

Hemp plants grow considerably tall and thick, and in the period of just one year they accumulate a large biomass. Surprisingly, this rate of growth requires little human input and is largely constant across different environmental conditions. The fact that hemp has been planted from the tropics up to the Arctic circle stands as an example of its robustness.

The high-quality cellulose found in the plant's stem, the oil in its seeds and the resins in its flowers have been put to use in over 50,000 distinct applications. Among others, these include fabrics, ropes, paper, nutritional food, medicine, cosmetics, and biofuels. Add to this the fact that hemp plants have a positive impact on the environment, and it becomes apparent how hemp could contribute to a robust sustainable economy.

Despite its many advantages and long history, global hemp cultivation declined steeply after the end of the Second World War. Hemp plantations were mostly displaced by cotton, which has a much higher environmental cost due to its extensive water and chemical requirements. Today, hemp is witnessing a sort of comeback, but it still remains far from previous levels of production.

Importantly, this 50-year period of relative abandonment coincided with a time in which modern science was driving substantial improvements in all other major crops. Thus, hemp’s full potential remains largely unknown.

In light of this, the European Union funded project "MultiHemp" with the goal of applying modern tools and research to optimize hemp crops. This project led to an interesting breakthrough, when earlier this year researchers from the Netherlands and Italy created a mathematical model that describes hemp’s unique photosynthesis capability. Their report can be freely accessed in the journal Global Change Biology: Bioenergy.

The research project boiled down to testing the levels of photosynthesis of hemp plants maintained in different conditions. As would be expected, their potential increased linearly with the level of nitrogen added to the soil. It also varied based on atmospheric temperature, increasing as temperature rose to 25 °C and then levelling off between 25°C and 35°C, before declining as temperature reached 40°C. The stable response between 25°C and 35°C reflects hemp’s ability to thrive in a large range of climates.

By using a myriad of tools and conditions, the authors were able to identify a dozen or so parameters that describe hemp's photosynthesis in detail. This will hopefully assist researchers’ and bioengineers’ future efforts to improve hemp's yield. For the time being, it allows for a direct comparison between hemp's efficiency and that of other crops for which these parameters were already known.

The authors compared hemp with cotton and kenaf (an alternative to hemp in tropical and subtropical climates). The three plants seem to adapt similarly to changes in CO2 concentration, with a possible benefit to kenaf at very high levels. Hemp and Kenaf had a similar photosynthesis potential with varying light intensities, whereas cotton performed systematically worse. More striking was that hemp performed considerably better than either kenaf or cotton under low levels of nitrogen in the soil, which could account for its large autonomy.

This study hints at how much is still left to understand about hemp, while at the same time  reconfirming the plant’s potential role in a sustainable economy that aims at counteracting the pressing issues of climate change, natural resource scarcity and environmental pollution.

Featured image by Adrian Cable.

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