
Hemp plants could make textiles of the future more environmentally friendly. Because the fiber plants require significantly less fertilizer, pesticides and water than, for example, cotton, as a field test has now shown. According to this, common intoxicant-free hemp varieties use the available water six times more efficiently than cotton and produce sufficient biomass and fibers even in dry conditions. Whether this applies to all locations and weather conditions is still being researched.
Climate change has long been a reality – also here in Germany. Agriculture is suffering from water scarcity due to rising temperatures and the three consecutive years of poor rainfall. The same is true in many other regions around the world. This is particularly problematic for textile production, among other things. Because besides synthetic fibers, cotton is the most important supplier of textile fibers.
However, cotton cultivation is associated with an intensive use of pesticides, abundant fertilization and a high demand for water – the plants require at least 750 millimeters of precipitation or irrigation water per vegetation period. A possible alternative could therefore be more frugal fiber plants, including hemp (Cannabis sativa). This fiber plant, which was previously cultivated worldwide, is not very susceptible to pests and diseases, grows comparatively quickly and achieves high yields.
How efficiently do hemp plants use water?
But what about the water requirements of the hemp plants? Katrin Drastig and her colleagues from the Leibniz Institute for Agricultural Engineering and Bioeconomy in Potsdam have now investigated this question in a field test in 2017 and 2018. They examined the two intoxicant-free hemp varieties “Santhica 27” and “Ivory”, which grow in Central European locations. The investigations were carried out in the northwest of Potsdam – in one of the driest growing areas in Germany with an average annual rainfall of only 579 millimeters. In the extremely dry vegetation period of 2018 it was significantly less. The researchers sowed the hemp seeds on the sandy soil typical of this area, which stores very little water and nutrients.
In the course of the experiment, Drastig and her team documented meteorological data and the availability of water from the soil as well as the water balance of the hemp plants. To do this, they recorded their water content, gas exchange, photosynthesis performance and also how much moisture the plants gave off through their leaves. Immediately after the harvest, the research team determined the biomass and the amount of fibers it contained. With the help of this data, they finally calculated the water productivity – i.e. the relationship between the water requirement and the build-up of dry matter in the hemp plants.
Efficient hemp cultivation even in dry locations
The result: The examined hemp varieties grew very efficiently in the observed period despite the dry periods. According to this, the industrial hemp produced an average of 2.4 kilograms of dry matter per cubic meter of water used, around 60 percent of which are fibers. The variety “Santhica 27” achieved slightly more yields than “Ivory”, although with both varieties the rainwater that was captured penetrated the canopy to the same extent and evaporated. The different growth of the plants could, among other things, be related to the fact that the roots of some plants reached the groundwater better, suspect Drastig and her colleagues.
Their results make the advantages of hemp cultivation clear: “We see that hemp offers great potential for cultivation in relatively dry locations,” says Drastig’s colleague Hans-Jörg Gusovius. “The THC-free cannabis varieties used here and specially bred for growing conditions in Europe are also suitable for cultivation in rather dry locations.” According to the researchers, the water productivity of the hemp varieties examined is about six times higher than that of cotton. With the same amount of water, this produces only about 0.4 kilograms of dry matter and must therefore be cultivated or irrigated in damp locations. “That makes fiber hemp interesting as an environmentally friendly alternative to cotton, also thanks to the lower demands on plant protection,” Gusovius continues.
Other plants in focus too
According to the scientists, their results are a first step forward in the search for alternatives to “thirsty” cotton. However, the current study only sheds light on one location and one time period. Therefore, there is still a considerable need for research in order to better prepare agriculture for future climate scenarios. “We need a lot more data in order to be able to derive models for specific regions, management practices and crop species from individual results. This would allow us to offer farmers decision support in optimizing water use, ”summarizes Drastig.
To this end, the team is already researching intensively on the more sustainable production of fiber raw materials such as flax and nettle, but also on the use of coupling and residual materials from food and feed crops such as hops, linseed or sorghum. Their high-quality plant fibers could possibly also replace insulation and building materials made from fossil raw materials in the future.
Source: Leibniz Institute for Agricultural Engineering and Bioeconomy eV (ATB), specialist article: Water, doi: 10.3390 / w12112982