Review
Key cultivation techniques for hemp in Europe and China

https://doi.org/10.1016/j.indcrop.2014.06.041Get rights and content

Highlights

  • The practical experience of hemp cultivation in Europe and China was reviewed.

  • Hemp holds a great potential in the frame of the developing bio-based economy.

  • Knowledge on the effects of G×M×E on hemp quality characteristics is limited.

  • New hemp varieties tailored to specific end-uses need to be developed.

Abstract

Hemp (Cannabis sativa L.) is a multiuse, multifunctional crop that provides raw material to a large number of traditional and innovative industrial applications. A relatively simple, low input cultivation technique and the sustainability of its products are the main drivers for a future expansion of the hemp crop. In Europe, the large political support of bioenergy in recent years has fuelled numerous studies on the potential cultivation of hemp for bioenergy production. In China the main drivers for a renewed interest in hemp are its traditional applications. For any given destination, the main target of hemp cultivation is the maximization of biomass production, but each end-use destination has specific quality requirements in terms of properties of the bast fibre, characteristics of the oil and proteins in the seeds, or profile of secondary metabolites in the inflorescence.

In this paper, traditional and innovative end use destinations and cultivation systems for hemp are introduced, together with some notes on hemp botany, biology, and resource use efficiency. This information, together with a review of the practical experience of hemp cultivation in Europe and China and knowledge gathered form scientific literature, highlights the effect of agronomic factors in determining the yield potential and quality level of hemp for specific end use destinations. To conclude, future perspectives and recommendations for hemp cultivation and research are discussed.

Introduction

Hemp (Cannabis sativa L.) is considered one of the oldest crops known to man. It is estimated that its use dates back to 10,000 years ago (Schultes et al., 1974) and an hypothesis of co-evolution of the genus Cannabis with the human species has been postulated (McPartland and Guy, 2004).

A recent chemotaxonomic study (Hillig, 2005) confirms the common belief that Cannabis had its origin and centre of diversity in Central Asia (Vavilov, 1952, de Candolle, 1883).

The history of hemp cultivation in China is as old as the history of civilization, and it can be dated back to at least 6000 years ago according to archaeological findings and ancient records (Yang, 1991). As reviewed by Yang (1991), general descriptions of the experience and agricultural cultivation practice were recorded in the book of Si Shengzhi, approximately one century B.C.; and the scenario of the hemp farming and retting were depicted as early as XiZhou Dynasty (11-7 century B.C.). Ancient documents of hemp cultivation and use in Europe are scarce. According to Erodotus (484 B.C.), Scythians brought hemp to Europe from Asia during their migrations 1500 years B.C., while Teutons had an important role in diffusing hemp cultivation throughout Europe (Schultes, 1970). Columella, in the 1st century A.C., is among the firsts to make reference to hemp cultivation (cited by Bruna, 1955) but indications to specific agricultural techniques are relatively vague also in Plinium who is generally very detailed in his agronomic descriptions (Schultes, 1970, Somma, 1923). Documents referring to hemp cultivation in Europe are relatively scarce until the 15th century when the importance of this species, mainly as fibre crop for the production of textiles and ropes, grew to attain an important and well-documented commercial role from the 18th to the 19th centuries. The progressive decline of hemp cultivation in Europe (Fig. 1) during the 20th century is to ascribe both to the progressive diffusion of synthetic fibres but also to the increasing cost of labour (Allavena, 1962).

Parallel to the use of hemp as a fibre crop is that as a medicinal plant, and as ritual, intoxicating drug (Russo, 2007). The gene flow between fibre and drug strains is however relatively small (Hillig, 2004) indicating a net separation between the two end use destinations of the plant that brought numerous authors to consider fibre hemp (C. sativa L.) and drug hemp (C. indica Lam.) as two separate species (Anderson, 1980, Schultes, 1973).

Despite the interesting nutritional value of hemp seeds (Callaway, 2004) reference to their use as human food in history is relatively small (Schultes, 1973). In the areas where commercial hemp cultivation is diffused, dedicated hemp crops for the production of seeds are planted, following a specific agronomic technique, to obtain seed for the future fibre hemp plantations (Bócsa and Karus, 1998).

This brief history of hemp cultivation has highlighted the potential of hemp as a multiuse crop, a potential that is one of the main features that has fuelled the recent come back of interest over the cultivation of hemp (Karus and Vogt, 2004). Examples of actual and potential innovative application of hemp fibre are numerous. The use of hemp for the production of paper dates back to more than 2000 years, and considering that until the 19th century, paper making depended exclusively on rags that were mainly made of flax and hemp, hemp is strictly linked with the history of paper making (Van Roekel, 1994).

Hemp fibre can be used as reinforcement in composites materials (Garcia-Jaldon et al., 1998), to produce insulation mats and car interior panels (Holbery and Houston, 2006), to reinforce expanded starch foams in the food packaging sector (Bénézet et al., 2012). In the bio-building sector hemp shives alone (Jarabo et al., 2012, Li et al., 2006, Elfordy et al., 2008) or shives together with bast fibres (de Bruijn et al., 2009) mixed with a binder (lime, clay, plaster, etc.) are used to form hemp concrete.

Recently the support granted to bioenergy production has fuelled research on the use of hemp for the production of ethanol (Prade et al., 2011, Sipos et al., 2010), biogas (Kreuger et al., 2011), and biomass for combustion (Aluru et al., 2013, Prade et al., 2011, Rice, 2008) and in a number of papers hemp is depicted as a valuable option to produce sustainable bioenergy (Finnan and Styles, 2013, Rehman et al., 2013).

The quality of the above mentioned products depends on quality characteristics of the hemp fibre and particularly on the morphology of the fibre bundles and on the chemical composition of the elementary fibre (Rowell et al., 2000). Suitability of hemp fibre in polymer reinforcement or biocomposites depends on various fibre features as fibre surface characteristics and fibre finesses that influence interfacial bond strength between the fibres and the matrix (Gamelas, 2013), and fibres tensile strength (Placet, 2009). Moreover, also the variability of natural fibre properties, moisture absorption and cost relative to fibre processing are weak factors of natural fibres for composite applications (Deyholos and Potter, 2013). In order to render hemp fibre suitable for industrial applications, in addition to various extraction processes, numerous chemical, biological and physical treatments to the fibre are possible (Korte and Staiger, 2008, Kostic et al., 2008, Kostic et al., 2010, Tak Oh et al., 2012) but selection of improved genotypes (Deyholos and Potter, 2013) and optimization of agrotechnique, on the basis of actual and future knowledge on the influence of agronomic factors on fibre characteristics (this paper), are valuable strategies to improve hemp fibre use in industrial applications. The integrity of the fibre characteristics is essential for the production of natural fibre reinforced composites suitable for structural applications. Mechanical processing, necessary for fibre extraction and preparation, are the main cause of damage to the fibres (Hänninen et al., 2012). These damages to the fibre cell wall structure, often called dislocations, or nodes or slip planes have also been observed in unprocessed fibres (Hartler, 1995, Thygesen, 2011, Thygesen and Asgharipour, 2008) but there is no indication of a specific genetic predisposition to the appearance of dislocations on hemp fibres nor of the potential impact of cultivation system and environmental conditions on the occurrence of fibre damage.

Hemp seeds are traditionally used in food and folk medicinal preparations (Jones, 1995) or employed as a feed for birds and fishes (Deferne and Pate, 1996). Recent characterization of oil (House et al., 2010, Latif and Anwar, 2009, Callaway, 2004, Kriese et al., 2004) and protein isolates (Tang et al., 2006, Tang et al., 2009, Wang et al., 2008) from hemp seeds have highlighted that not only the fibre but also the seeds hold very interesting commercial potential in food (Callaway, 2004, Matthäus and Brühl, 2008), feed (Hessle et al., 2008, Goldberg et al., 2012) and cosmetic applications (Sapino et al., 2005, Vogl et al., 2004).

Considering that in traditional hemp cultivation harvesting was set at flowering, when fibre quality is optimal for textile destination (Bócsa and Karus, 1998), the production of hemp seeds was carried out in ad hoc cultivations with low plant density (ITC, 2007, Hennink et al., 1994, Van der Werf, 1994, Venturi, 1965). The increased commercial interested on hemp seeds (Bouloc, 2013), the need to maximize economic return from the cultivation and the general call to manage biomass crops following the biorefinery concept (www.multihemp.eu) is stimulating a progressive shift towards the cultivation of dual purpose hemp crops, where both the stem and the seeds are harvested. Agronomic techniques and genotypes should be adapted to preserve fibre quality during grain ripening.

While fibre and seed are the main products, there is a growing interest over the valorization of hemp secondary metabolites. Hemp vegetative and reproductive organs are rich in various unique bioactive secondary metabolites, namely cannabinoids, terpenoids and flavonois (Hazekamp et al., 2010). The possibility to use hemp extracts in pharmaceutical applications (Appendino et al., 2008), as bio-pesticides against nematodes (Mukhtar et al., 2013), mesophilic fungi (Grewal, 1989), insects (Zia et al., 2011, Gorski et al., 2009) and potentially weeds (Flamini, 2012) opens a new challenge to set up a cultivation system with the use of specific varieties and cultivation techniques, coupled to an harvesting and processing system that allows the production of good quality fibre, seeds and the recovery of valuable secondary metabolites. A similar approach is researched and developed in the frame of the EU project Multihemp (www.multihemp.eu).

The appeal of hemp for modern agriculture is not only linked to its multifold applications but also to the positive impact on the environment of its products and cultivation. Hemp has been positively evaluated for its cultivation on contaminated soils (Ivanova et al., 2003, Citterio et al., 2005, Gryndler et al., 2008) and generally it is considered that it can be grown without pesticides (Desanlis et al., 2013) and with a low input technique (Struik et al., 2000).

In this work the most relevant aspects of hemp cultivation will be reviewed to highlight how the quantity and quality of hemp fibre production is determined by different agronomic factors. The challenges being faced when hemp is cultivated for both fibre and seeds will also be discussed.

Sections 2 Hemp botany, biology and resource use efficiency, 3 Influence of agronomic factors on industrial hemp review the biological and agronomic aspects relevant to hemp cultivation and Section 4 describes the actual agronomic techniques used in Europe and China, two regions that have cultivated hemp throughout history and are committed to its resurgence as a multipurpose crop.

Section snippets

Hemp botany and hemp biology

Hemp is an annual dicotyledonous angiosperm plant belonging to the Rosales order; sub-order Rosidae and Cannabaceae family (Chase, 1998). Naturally it is dioecious, with the staminate plants that are usually slender, taller and that come to flower earlier that the pistillate ones. Hemp is wind pollinated and the male plants die after producing millions of pollen grains. A small percentage of monoecious plant can naturally occur, particularly in short-day conditions (Dempsey, 1975). Monoecious

Soil preparation

Preparation of a fine and homogenous seed-bed is an important condition to obtain a uniform establishment and a homogeneous crop presenting the desired plant density (Struik et al., 2000).

Soil preparation for hemp is similar to that of other break crops. Usually, fall or winter ploughing (at 30–40 cm depth) followed by preparation of a fine seedbed in the spring, just before sowing and depending on the soil physic characteristics, are the recommended tillage practices for hemp, especially on

Hemp cultivation in Europe

Once a very important industrial crop, hemp decline after II World War has been unstoppable and at the end of the 1960s it had almost disappeared from most of the Western European countries. A renewed interest on hemp cultivation started in the early 1990s when the cultivation of hemp was reauthorized throughout the European Union. After more than 20 years hemp is still a niche crop, cultivated on 10,000–15,000 ha in the European Union (Carus et al., 2013). In the last 30 years, France has been

Conclusion

Hemp is a niche crop that holds a great potential in the frame of the developing bio-based economy.

A relatively large scientific literature dealing with the effect of environment and cultivation practices on hemp production is available, while limited information is available on the effect of environment and management on plant quality characteristics (of fibre, seed and secondary metabolites). Evaluation of commercial varieties on the basis of their suitability to different end use application

Acknowledgements

This work was supported by FIBRA project (Fibre Crops as a Sustainable Source of Bio-based Materials for Industrial Products in Europe and China), funded by the EU Seventh Framework Programme under the Grant Agreement 311965.

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