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ARTICLE IN PRESSG ModelNDCRO-7384; No. of Pages 15

Industrial Crops and Products xxx (2014) xxx–xxx

Contents lists available at ScienceDirect

Industrial Crops and Products

jo ur nal home p age: www.elsev ier .com/ locate / indcrop

eview

ey cultivation techniques for hemp in Europe and China

. Amaduccia,∗, D. Scordiab,1, F.H. Liuc, Q. Zhangd,2, H. Guod,2,. Testab,1, S.L. Cosentinob,1

Istituto di Agronomia, Genetica e Coltivazioni erbacee, Facoltà di Agraria, Università Cattolica del Sacro Cuore, Via Emilia Parmense, 84, 29122 Piacenza,talyDipartimento di Scienze delle Produzioni Agrarie e Alimentari, University of Catania, Via Valdisavoia 5, 95123 Catania, ItalyFaculty of Agriculture, Yunnan University, 2 North Cuihu Lake Road, 650091 Kunming, PR ChinaIndustrial Crops Research Institute, Yunnan Academy of Agricultural Sciences (YAAS), 650205, Longtou Street, Kunming, PR China

r t i c l e i n f o

rticle history:eceived 28 February 2014eceived in revised form 31 May 2014ccepted 20 June 2014vailable online xxx

eywords:annabis sativaempgronomyroduction

a b s t r a c t

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

In this paper, traditional and innovative end use destinations and cultivation systems for hemp are
ibre qualityesource use efficiency
introduced, together with some notes on hemp botany, biology, and resource use efficiency. This infor-mation, together with a review of the practical experience of hemp cultivation in Europe and China andknowledge gathered form scientific literature, highlights the effect of agronomic factors in determin-ing the yield potential and quality level of hemp for specific end use destinations. To conclude, futureperspectives and recommendations for hemp cultivation and research are discussed.

© 2014 Elsevier B.V. All rights reserved.

ontents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 002. Hemp botany, biology and resource use efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

2.1. Hemp botany and hemp biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 002.1.1. Description of the plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

2.2. Resource use efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003. Influence of agronomic factors on industrial hemp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3.1. Soil preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.2. Variety choice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.3. Sowing time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.4. Plant density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.5. Plant nutrition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

Please cite this article in press as: Amaducci, S., et al., Key cultivation thttp://dx.doi.org/10.1016/j.indcrop.2014.06.041

3.6. Role of hemp in the crop rotations and weed management . . . . . . .3.7. Irrigation, how the availability of water affects yield and quality .3.8. Harvesting time as a function of end use destination (fibre + seed)

∗ Corresponding author. Tel.: +39 0523599223.E-mail addresses: [email protected] (S. Amaducci), [email protected] (D. Sco

G. Testa), [email protected] (S.L. Cosentino).1 Tel.: +39 095234350.2 Tel.: +86 871 65896251; fax: +86 871 65893201.

ttp://dx.doi.org/10.1016/j.indcrop.2014.06.041926-6690/© 2014 Elsevier B.V. All rights reserved.

echniques for hemp in Europe and China. Ind. Crops Prod. (2014),

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

rdia), [email protected] (F.H. Liu), [email protected] (Q. Zhang), [email protected]

dx.doi.org/10.1016/j.indcrop.2014.06.041


http://www.sciencedirect.com/science/journal/09266690

http://www.elsevier.com/locate/indcrop

mailto:[email protected]







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4. Actual hemp cultivation and future perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 004.1. Hemp cultivation in Europe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 004.2. Hemp cultivation in China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

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References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. Introduction

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

A recent chemotaxonomic study (Hillig, 2005) confirms theommon belief that Cannabis had its origin and centre of diversityn Central Asia (Vavilov, 1952; de Candolle, 1883).

The history of hemp cultivation in China is as old as the his-ory of civilization, and it can be dated back to at least 6000 yearsgo according to archaeological findings and ancient records (Yang,991). As reviewed by Yang (1991), general descriptions of thexperience and agricultural cultivation practice were recorded inhe book of Si Shengzhi, approximately one century B.C.; and thecenario of the hemp farming and retting were depicted as early asiZhou Dynasty (11-7 century B.C.). Ancient documents of hempultivation and use in Europe are scarce. According to Erodotus484 B.C.), Scythians brought hemp to Europe from Asia during their

igrations 1500 years B.C., while Teutons had an important rolen diffusing hemp cultivation throughout Europe (Schultes, 1970).olumella, in the 1st century A.C., is among the firsts to make ref-rence to hemp cultivation (cited by Bruna, 1955) but indicationso specific agricultural techniques are relatively vague also in Plin-um who is generally very detailed in his agronomic descriptionsSchultes, 1970; Somma, 1923). Documents referring to hemp cul-ivation in Europe are relatively scarce until the 15th century whenhe importance of this species, mainly as fibre crop for the pro-uction of textiles and ropes, grew to attain an important andell-documented commercial role from the 18th to the 19th cen-

uries. The progressive decline of hemp cultivation in Europe (Fig. 1)uring the 20th century is to ascribe both to the progressive diffu-


ion of synthetic fibres but also to the increasing cost of labourAllavena, 1962).

ig. 1. Hemp area harvested (×1000 ha) in two representative European countriesFrance and Italy) from 1840 up to 1960 and from 1960 up to 2012 in Europe andhina.

ource: FAO-Stat, Nova-Institut.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

Parallel to the use of hemp as a fibre crop is that as a medicinalplant, and as ritual, intoxicating drug (Russo, 2007). The gene flowbetween fibre and drug strains is however relatively small (Hillig,2004) indicating a net separation between the two end use destina-tions of the plant that brought numerous authors to consider fibrehemp (C. sativa L.) and drug hemp (C. indica Lam.) as two separatespecies (Anderson, 1980; Schultes, 1973).

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

This brief history of hemp cultivation has highlighted the poten-tial of hemp as a multiuse crop, a potential that is one of the mainfeatures that has fuelled the recent come back of interest over thecultivation of hemp (Karus and Vogt, 2004). Examples of actual andpotential innovative application of hemp fibre are numerous. Theuse of hemp for the production of paper dates back to more than2000 years, and considering that until the 19th century, paper mak-ing depended exclusively on rags that were mainly made of flax andhemp, hemp is strictly linked with the history of paper making (VanRoekel, 1994).

Hemp fibre can be used as reinforcement in composites materi-als (Garcia-Jaldon et al., 1998), to produce insulation mats and carinterior panels (Holbery and Houston, 2006), to reinforce expandedstarch foams in the food packaging sector (Bénézet et al., 2012). Inthe bio-building sector hemp shives alone (Jarabo et al., 2012; Liet 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 hasfuelled 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 valu-able option to produce sustainable bioenergy (Finnan and Styles,2013; Rehman et al., 2013).

The quality of the above mentioned products depends on qualitycharacteristics of the hemp fibre and particularly on the morphol-ogy of the fibre bundles and on the chemical composition of theelementary fibre (Rowell et al., 2000). Suitability of hemp fibrein polymer reinforcement or biocomposites depends on variousfibre features as fibre surface characteristics and fibre finessesthat influence interfacial bond strength between the fibres andthe 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 weakfactors of natural fibres for composite applications (Deyholos andPotter, 2013). In order to render hemp fibre suitable for industrialapplications, in addition to various extraction processes, numerouschemical, biological and physical treatments to the fibre are possi-


ble (Korte and Staiger, 2008; Kostic et al., 2008, 2010; Tak Oh et al.,2012) but selection of improved genotypes (Deyholos and Potter,2013) and optimization of agrotechnique, on the basis of actualand future knowledge on the influence of agronomic factors on


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bre characteristics (this paper), are valuable strategies to improveemp fibre use in industrial applications. The integrity of the fibreharacteristics is essential for the production of natural fibre rein-orced composites suitable for structural applications. Mechanicalrocessing, necessary for fibre extraction and preparation, are theain cause of damage to the fibres (Hänninen et al., 2012). These

amages to the fibre cell wall structure, often called dislocations,r nodes or slip planes have also been observed in unprocessedbres (Hartler, 1995; Thygesen, 2011; Thygesen and Asgharipour,008) but there is no indication of a specific genetic predispositiono the appearance of dislocations on hemp fibres nor of the poten-ial impact of cultivation system and environmental conditions onhe occurrence of fibre damage.

Hemp seeds are traditionally used in food and folk medicinalreparations (Jones, 1995) or employed as a feed for birds and fishesDeferne and Pate, 1996). Recent characterization of oil (Houset al., 2010; Latif and Anwar, 2009; Callaway, 2004; Kriese et al.,004) and protein isolates (Tang et al., 2006, 2009; Wang et al.,008) from hemp seeds have highlighted that not only the fibreut also the seeds hold very interesting commercial potential inood (Callaway, 2004; Matthäus and Brühl, 2008), feed (Hessle et al.,008; Goldberg et al., 2012) and cosmetic applications (Sapino et al.,005; Vogl et al., 2004).

Considering that in traditional hemp cultivation harvesting waset at flowering, when fibre quality is optimal for textile destina-ion (Bócsa and Karus, 1998), the production of hemp seeds wasarried out in ad hoc cultivations with low plant density (ITC, 2007;ennink et al., 1994; Van der Werf, 1994; Venturi, 1965). The

ncreased commercial interested on hemp seeds (Bouloc, 2013),he need to maximize economic return from the cultivation andhe general call to manage biomass crops following the biorefin-ry concept (www.multihemp.eu) is stimulating a progressive shiftowards the cultivation of dual purpose hemp crops, where bothhe stem and the seeds are harvested. Agronomic techniques andenotypes should be adapted to preserve fibre quality during grainipening.

While fibre and seed are the main products, there is a grow-ng interest over the valorization of hemp secondary metabolites.emp vegetative and reproductive organs are rich in variousnique bioactive secondary metabolites, namely cannabinoids, ter-enoids and flavonois (Hazekamp et al., 2010). The possibility to useemp extracts in pharmaceutical applications (Appendino et al.,008), as bio-pesticides against nematodes (Mukhtar et al., 2013),esophilic fungi (Grewal, 1989), insects (Zia et al., 2011; Gorski

t al., 2009) and potentially weeds (Flamini, 2012) opens a newhallenge to set up a cultivation system with the use of specificarieties and cultivation techniques, coupled to an harvesting androcessing system that allows the production of good quality fibre,eeds and the recovery of valuable secondary metabolites. A sim-lar approach is researched and developed in the frame of the EUroject Multihemp (www.multihemp.eu).

The appeal of hemp for modern agriculture is not only linkedo its multifold applications but also to the positive impact on thenvironment of its products and cultivation. Hemp has been posi-ively evaluated for its cultivation on contaminated soils (Ivanovat al., 2003; Citterio et al., 2005; Gryndler et al., 2008) and generallyt is considered that it can be grown without pesticides (Desanlist al., 2013) and with a low input technique (Struik et al., 2000).

In this work the most relevant aspects of hemp cultivation wille reviewed to highlight how the quantity and quality of hempbre production is determined by different agronomic factors. Thehallenges being faced when hemp is cultivated for both fibre and


eeds will also be discussed.Sections 2 and 3 review the biological and agronomic aspects

elevant to hemp cultivation and Section 4 describes the actualgronomic techniques used in Europe and China, two regions that

Fig. 2. From bottom to top, hemp stem cross section and fruit longitudinal section(modified by Hayward, 1938).

have cultivated hemp throughout history and are committed to itsresurgence as a multipurpose crop.

2. Hemp botany, biology and resource use efficiency

2.1. Hemp botany and hemp biology

Hemp is an annual dicotyledonous angiosperm plant belongingto the Rosales order; sub-order Rosidae and Cannabaceae family(Chase, 1998). Naturally it is dioecious, with the staminate plantsthat are usually slender, taller and that come to flower earlier thatthe pistillate ones. Hemp is wind pollinated and the male plantsdie after producing millions of pollen grains. A small percentageof monoecious plant can naturally occur, particularly in short-day conditions (Dempsey, 1975). Monoecious varieties have beenselected in modern times to reduce the agronomic problems relatedto the sexual vegetative dimorphism present in dioecious varieties,in particular the lack of an efficient mechanization for harvestingthe seeds, and the lower fibre quality and yield losses encounteredwhen harvesting dioecious varieties at seed maturity (Berenji et al.,2013; Faux et al., 2013).

2.1.1. Description of the plantThe hemp stem consists of different morphological regions and

in a transversal section, from the outer to the inner part of the stem,the following elements can be recognized: an external layer com-posed of a thin epidermis, and hypodermis and a chlorenchyma; alayer where parenchyma cells separate bundles made of primarybast fibres that are bound together by their middle lamella; inmature stems a layer of small and lignified secondary bast fibresfollows; the cambium; further inside the woody core with lignifiedcells, woody fibres, vessels and ray cells and the pith (Fig. 2).

The cultivation of industrial hemp traditionally targets the pro-


duction of primary bast fibres, any factor affecting their quantityand characteristics should be controlled in order to have fibres suit-able to specific end use destinations. In the following sections of thepaper the influence of agronomic factors affecting fibre production


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ill be discussed. It should be noted, however, that the fibre charac-eristics have a natural variation within each plant independentlyf the growing techniques. A gradient of fibre finesses and fibreaturity is found along the stem with coarser fibres at the bot-

om and finer ones in the top part of the stem (Amaducci et al.,008a). A similar gradient is found for fibre maturity. Fibres with aigher degree of lumen filling are found at the bottom, while imma-ure fibres are at the top (Amaducci et al., 2005a, 2008a; Medeghinionatti et al., 2004). Considering that maturation of fibre cells pro-eeds from the outer to the inner part of the stem, a gradient of fibreaturity is also found within the same cross section of an intern-

de with more mature fibre found in the external part of the bundleAmaducci et al., 2005a).

In traditional dioecious fibre varieties a variation in fibre contentnd characteristics is present between male and female plants. Inarticular male plants have more primary fibre, a higher proportionf primary to secondary fibres and generally show superior qual-ty characteristics of the primary fibre, a part from a lower tensiletrength (Bócsa and Karus, 1998).

Compared to the valuable and commercially interesting bastbre little information is available on wood fibres, also called hurdsr shives. Various authors report on different features of woodnatomy and chemistry but little is known on the factors affectinghese features. Anderson (1974) describing the wood anatomy of a. indica in comparison with a C. sativa found surprising differences

n wood cell distribution, cell wall thickness and cell dimension.n the contrary, De Meijer (1994) analysing 160 hemp accessions

ound very limited variation in wood fibre dimension among geno-ypes.

Li et al. (2013) have studied the variation of hemp xylem fibresn mature stems, and they found that fibres are shorter in the lowerart of the stem (0.51 mm) and longer in the top part (0.57 mm).ibre diameter also showed a diameter gradient along the stemith wider cells at the bottom (32.2 �m) and thinner ones at the

op (25.6 �m). Xylem fibre lumen and cell wall thickness was alsoarger at the bottom (20.4 and 5.92 �m, respectively) and decreasedn the top (17 and 4.34 �m) portion of the stem. Regarding otherell wall characteristics Micro Fibril Angle (MFA) was constantlong the stem height (on average 10.6◦) while the degree of crys-allinity tended to decrease (50.7–51.7% in the bottom 10–60 cmnd 49.9–48.2% in the top 110–210 cm).

The hemp fruits, commonly referred to as seeds, are small dryuts, botanically termed as achene (Fig. 2). The fruit contains a sin-le seed surrounded by a thin pericarp. The seed is elliptical andhe large part of its mass is made of two cotyledons that are richn reserve substances (Bócsa and Karus, 1998). A small radicle, tworue leaves and a thin nutritive tissue are also present (Small andntle, 2007). The weight of the achenes is very variable and it ranges

rom 2 g up to 70 g per 1000 seeds. Usually seeds in monoeciousarieties are smaller than in dioecious ones (Bócsa and Karus, 1998).

Hemp has a wide range of environmental adaptation butarieties tend to perform better in their areas of developmentDempsey, 1975). In hemp a very relevant aspect of the adapta-ion to a specific environment is the sensitivity to photoperiodAmaducci et al., 2012). Flowering time is a very important fac-or in hemp yield determination, both in terms of quantity (Vaner Werf et al., 1994a, 1996; Struik et al., 2000) and quality (Kellert al., 2001; Mediavilla et al., 2001; Amaducci et al., 2005a, 2008a).avidjan (1971) grouped Russian hemp varieties according to threeeographical areas, Northern, Middle-Russian and Southern andescribed that varieties from the Southern areas extended theiregetative cycles and failed to produce seeds when moved to the


orth. On the contrary, Northern varieties produced seeds and veryhort crops when moved to the South. Similar results are reportedor Western European conditions (Amaducci et al., 2012; Pahkalat al., 2008) and for China (Guo et al., 2013; Yao et al., 2007).

PRESSd Products xxx (2014) xxx–xxx

The very evident response of hemp to sub-optimal photoperiodsis well documented in the literature; “pre-flowering” would occurin South Italy when hemp seeds were imported from Northerncountries (Barbieri, 1952) or as recently experimented by Cosentinoet al. (2012). Tournois (1912) working on hemp was the first topresent experimental evidence of the effect of photoperiod on plantdevelopment.

A standardized phenological scale based on the decimal codeof Zadoks et al. (1974) was proposed for hemp by Mediavilla et al.(1998). Accordingly the hemp cycle was divided in four growthstages: Germination and emergence; Vegetative stage; Floweringand seed formation; Senescence. Phenological models proposed byLisson et al. (2000b) and Amaducci et al. (2008a) further dividethe vegetative phase in three phases: juvenile phase (BVP), photo-sensitive phase (PIP) and flower development phase (FDP).

Hemp is a short-day plant (Heslop-Harrison and Heslop-Harrison, 1969) and its critical photoperiod, that according toHadley et al. (1984) is the daylenght under which the crop isinduced to flower if the BVP has been satisfied, corresponds toapproximately 14 h (Amaducci et al., 2008b, 2012; Lisson et al.,2000b).

The effect of temperature on hemp pre- and post-emergencedevelopment data are relatively scarce. A base temperature of 1 ◦Cis proposed for emergence and vegetative growth (Lisson et al.,2000a; Van der Werf et al., 1995a).

2.2. Resource use efficiency

Beside high yield potential, an important characteristic for anindustrial crop, adapted to modern sustainable production sys-tems, is the capacity to use resources effectively. The higher isthe resource use efficiency of a crop, the higher is the yield fora given level of the resource and the lower is the impact on theenvironment.

Main abiotic resources that influence plant growth are air andsoil temperature, global solar radiation, nutrients and water avail-ability.

The relationship between biomass production per unit of inter-cepted photosynthetically active radiation (iPAR) adsorbed by thecrop is known as radiation use efficiency (RUE).

In hemp, during the first weeks after emergences most of thedry matter is partitioned to the leaves leading to fast canopy clo-sure and enhanced iPAR (Meijer et al., 1995). Earlier canopy closurein spring, when incident PAR is high, results in a greater amount ofradiation intercepted and higher biomass production. In hemp 90%interception of PAR is attained earlier with high compared to lowplant populations. Amaducci et al. (2002b) reported that maximumPAR interception was reached at 582, 494, 467, 335, 300 ◦Cd respec-tively for 30, 45, 90, 180, 270 plants m−2. Meijer et al. (1995) foundthat a crop sown at 100 plants m−2 reached the same light intercep-tion level at 450–500 ◦Cd and Van der Werf et al. (1995a) reported396 ◦Cd to reach canopy closure considering a base temperature forleaf appearance of 1.0 and 2.5 ◦C for canopy establishment.

RUE of 2.0–2.2 g MJ−1 of PAR during development stage, and of1.1–1.2 g MJ−1 after flowering, was observed in Northern Europe(Meijer et al., 1995). Van der Werf et al. (1994a) obtainedsimilar results preventing flowering (2.3 g MJ−1) and 0.6 g MJ−1

post-flowering, when flowering was not prevented. A very latecultivar maintained a high RUE (2.2–2.3 g MJ−1) until it floweredin September compared to other cultivars which flowered earlier(August) and showed lower RUE (1.9 g MJ−1) (Van der Werf et al.,1995b). Struik et al. (2000) found a RUE of 2.16–2.26 g MJ−1 before


flowering and 1.09–0.95 g MJ−1 after flowering in fibre hemp grownin The Netherlands and Italy, respectively.

Decline in the RUE post-flowering has been associated to lossesof shed leaves, increase in growth respiration due to the synthesis of



S. Amaducci et al. / Industrial Crops and Products xxx (2014) xxx–xxx 5

Table 1Radiation use efficiency (g MJ−1) of different hemp varieties according to the treatment, geographic coordinates of the experimental site and maximum solar global radiation(or iPAR) at each site.

Variety Treatment Latitude/longitude Country Max. Solar glob. Rad.(MJ m−2 d−1)

RUE (g MJ−1) Reference

Fédrina 74 Plant density (20–80 kg ha−1) 51◦56′ N; 5◦43′ E The Netherlands 15.3 1.11–2.20 Meijer et al. (1995)Fédrina 74 Prevented flowering 51◦56′ N; 5◦43′ E The Netherlands 5.84–6.09 (iPAR) 0.93–1.82 Van der Werf et al. (1994a)Kompolti Hybrid TC Prevent flowering 51◦56′ N; 5◦43′ E The Netherlands 4.77–5.11 (iPAR) 0.16–2.82 Van der Werf et al. (1994a)Kompolti Hybrid TC Plant density (10–270 p m−2) 51◦56′ N; 5◦43′ E The Netherlands 0.45–6.44 (iPAR) 1.12–2.35 Van der Werf et al. (1995b)Hyper Elite Plant density (90 p m−2) 51◦56′ N; 5◦43′ E The Netherlands 2.15–8.34 (iPAR) 1.54–2.22 Van der Werf et al. (1995b)Kozuhara zairai Plant density (90 p m−2) 51◦56′ N; 5◦43′ E The Netherlands 2.02–8.30 (iPAR) 1.76–2.29 Van der Werf et al. (1995b)Fedora 19, Félina 74,

Futura 77,Kompolti

Maturity group, plant density,N fertilization

– The Netherlands – 1.09–2.16 Struik et al. (2000)

Félina 74, Futura 77,Carmagnola

Maturity group, plant density,N fertilization

– Italy – 0.95–2.26 Struik et al. (2000)

Futura 75 Irrigation (0*–100% ETmrestitution)

37◦25′ N; 15◦30′ E Italy 28.0 1.88–2.21 Cosentino et al. (2013)

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at and protein in the seeds, reduction of crop gross photosynthesisue to senescence of the canopy and synthesis of lignin in the stemsMeijer et al., 1995; Van der Werf et al., 1996).

A reduction of RUE can be observed with high level of inci-ent PAR, leading to light saturation in the leaves at the top of theanopy (Meijer et al., 1995) or if the crop experiences drought stressCosentino et al., 2013). Indeed, in South Europe a RUE of 2.21 and.88 g MJ−1 was reported when hemp was irrigated at 100% maxi-um evapotranspiration (ETm) restitution or 25% ETm restitution,

espectively. Under water stress conditions leaf area index (LAI),otal leaf biomass and as a consequence iPAR, canopy photosyn-hesis, RUE and aboveground biomass yield decreased (Cosentinot al., 2013) (Table 1).

Hemp RUE values are at the lower range found for other C3 cropss sunflower, rice, wheat, potato, chicory and Jerusalem artichokeMeijer et al., 1993, 1995). On the contrary, due to the planophileature of the hemp canopy and the high LAI (Meijer et al., 1995),

ight extinction coefficient (KL) is at the upper end of the rangeeported for many other crops.

Very few information on hemp water use efficiency (WUE)ave been reported so far. In the South of Europe, whereater shortage limits the yield of several spring-summer crops,osentino et al. (2013) showed that WUE ranged between 1.91nd 2.48 g biomass L−1 at early harvest (beginning of flowering),hile between 2.73 and 3.45 g biomass L−1 at the end of flower-

ng, respectively for 100% ETm restitution and irrigation until cropstablishment treatments. Lower WUE values have been reportedy Di Bari et al. (2004) (0.84–1.67 g bark L−1 for 100% and 33%estoration of the available water, respectively).

In general, in well water condition the water used by the cropxceeded the need of the crop itself (luxury consumption) and this


ould explain the correspondent lower WUE (Table 2).Due to its rapid growth, hemp requires substantial available

utrients to produce high biomass yields. Nitrogen use efficiencyNUE) for many crops, including hemp, is not quantified to date.

able 2ater use efficiency (g L−1) of different hemp varieties according to the treatment, geogr

Variety Treatment Latitude/longitude Countr

Fibranova, Red Petiole, Kompolti Irrigation 41◦ N; 4◦39′ E Italy

Futura 75 Irrigation (harvestbefore flowering)

37◦25′ N; 15◦30′ E Italy

Futura 75 Irrigation (harvestafter flowering)

37◦25′ N; 15◦30′ E Italy

* Irrigation until crop establishment

Among different NUE calculations, agronomic efficiencyexpresses the kg yield increase per kg nutrient applied (Mosier et al.,2004). Generally, at low yield a high efficiency is achieved since asmall amount of nutrient applied gives a large yield response.

In Table 3 NUE of different hemp varieties, according to N fer-tilization rates in different field trials is shown. Large differenceswere observed according to the available literature data. NUE var-ied between 7.5 (kg stem yield kg N−1) to 61.7 (kg biomass yield kgN−1).

3. Influence of agronomic factors on industrial hemp

3.1. Soil preparation

Preparation of a fine and homogenous seed-bed is an importantcondition to obtain a uniform establishment and a homogeneouscrop 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 bypreparation of a fine seedbed in the spring, just before sowing anddepending on the soil physic characteristics, are the recommendedtillage practices for hemp, especially on clay soils (Desanlis et al.,2013).

It was observed in Shandong Province (China) that soil texture,cation exchange capacity, soil organic matter, available potassiumand water-soluble boron in the soil are positively correlated withfibre hemp yield (Liu et al., 2000a). A suitable soil for hemp growthshould have pH 6.0–7.5; it should be deep, rich in capillary andaeration, rich in nutrients and have a good water holding capacity.Li (1982) suggested that sandy loam is the best for hemp growth,followed by clay loam, while heavy clay soil and sandy soil are not


well suitable. Indeed, even if the hemp tap-root is powerful andcan penetrate clay soil to a depth of about 2 m (Amaducci et al.,2008c), the presence of a compaction layer can limit root develop-ment and particularly when the compaction pan is superficial (i.e.

aphic coordinates of the experimental site and water supplied.

y Water supplied(mm)

Water restored(%)

WUE (g L−1) Reference

262–680 33–100 1.67–0.84 Di Bari et al. (2004)140–252 0*–100 2.48–1.91 Cosentino et al. (2013)

140–370 0*–100 3.45–2.73 Cosentino et al. (2013)



ARTICLE ING ModelINDCRO-7384; No. of Pages 15

6 S. Amaducci et al. / Industrial Crops an

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as a consequence of poor soil preparation, particularly in fine soils)the tap root takes on a L-shape that negatively affects the absorp-tion of nutrients and water by the crop (Desanlis et al., 2013). Inaddition, a poor soil preparation in wet years on clay soils resultsin waterlogging, which can severely affect the success of the crop(Struik et al., 2000). On the other hand, sandy soils with a low waterholding capacity can severely affect seedling emergence.

Fertilizers are generally applied as a broadcast treatment in thespring, prior to final seedbed preparation (P and K or organic mat-ter), while N is usually applied simultaneously or just before thesowing time.

Seed drills are used for hemp sowing at depth of 2–3 cm and rowdistance 9–17 cm (ITC, 2007). Seeding rate vary widely from 40 to150 kg ha−1 (Dempsey, 1975). Current recommended seeding ratesranges from 40 to 65 kg ha−1 to reach 200–300 plant m−2 for fibrehemp, decreasing to 20 kg ha−1 for seed hemp (ITC, 2007).

3.2. Variety choice

To choose a genotype suitable for a specific end use applicationand adapted to a particular environment is of paramount impor-tance to the success of hemp cultivation.

As it was already discussed, hemp phenology is strongly depen-dent on photoperiod and it is therefore possible to achieve a specificstem or seed yield in a given environment on the basis of thephotoperiod sensitivity of the selected variety. In non-limiting con-ditions stem yield is proportional to the duration of the vegetativephase and numerous experimental and practical evidences areavailable in literature showing that long vegetative growth, as aconsequence of late flowering time, results in high stem biomassproduction.

Cultivars bred in northern environments have lower biomassyield when grown in the South, mainly due to shortened growthduration and early-flowering (Guo et al., 2013; Cosentino et al.,2012; Amaducci et al., 2008b; Yao et al., 2007; Meijer et al., 1995;Barbieri, 1952). On the contrary, cultivars bred at low latitude havelate flowering and high biomass yields when cultivated at higherlatitudes (Guo et al., 2010; Hu et al., 2012; Pahkala et al., 2008;Sankari, 2000). Hu et al. (2012) tested cultivars YunMa 1, YunMa2, YunMa 3 and YunMa 4 in Heilongjiang Province (North-easternChina), and found significantly higher fibre yields than the localvarieties, but none of the four cultivars produced mature seeds.Jin (2009) compared 10 cultivars of hemp, 5 from the high lati-tude areas of China and 5 from Middle-latitude of Europe (Ukraine)and recommended cultivars Dnepr 6 and Golden Knife 15 fromUkraine for the production in Northern China. The cultivars rec-ommended for Southern China are YunMa cultivar series (bred inYunnan Province, Southwest China).

For those end-use applications where maximization of stembiomass is a priority, such as biomass production for bioenergy(Kreuger et al., 2011; Prade et al., 2011) or for pulp and paper (Kamatet al., 2002), selecting a late flowering variety seems the best option.

The choice is more complicated when the quality and not onlythe quantity is relevant to the end-use application. A large varia-tion in fibre content among genotypes has been reported. De Meijer(1994) did a unique comparison of 160 accessions and found that aminimal fraction of bark (10–15%) was found in drug strains, undo-mesticated populations and fibre landraces, while in varieties bredduring the 20th century the proportion of bark in the stem wasincreased from 25% up to 47% and the proportion of bast fibre in thebark from 40% to 68%. Despite the fact that the increase of total bast


fibre content brought about an increase of secondary bast fibre aswell, the breeding activity carried out in the 20th century has beensuccessful in increasing fibre content, but very limited informationis available on fibre quality characteristics of different varieties.


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In traditional dioecious hemp varieties the male plants haveuperior fibre quality characteristics and historically farmers handulled male plants to use their fibre for fine textile applicationshile female plants where used for coarse fabrics (Bócsa and Karus,

998). Modern breeding has been focused on the development ofonoecious varieties, which are better suited to the production of

bre and seeds (dual purpose crop) but it is considered that dioe-ious genotypes are superior for fibre production (Berenji et al.,013; Bócsa and Karus, 1998; Van der Werf et al., 1994b). Despitehe evidence that differences of fibre characteristics among geno-ypes exist (Amaducci et al., 2008a; Bennet et al., 2006; Cappellettot al., 2001; Sankari, 2000; Cromack, 1998; Van der Werf et al.,996, 1994b), the large variability of fibre characteristics withinhe same plant (Amaducci et al., 2005a, 2008a; Medeghini Bonattit al., 2004) or within the same genotype due to environmentalonditions (Sankari, 2000), the effect of the agronomic manage-ent (Berenji et al., 2013) and particularly the influence played

y the extraction methods (Müssig and Martens, 2003) render theelection of a specific variety for a defined end use particularlyifficult.

It can be concluded that for fibre production the best choicehould fall on a genotype that has a long vegetative cycle and higherbre content (Berenji et al., 2013). It should be noted however thathe choice of a late variety can have some drawbacks. In case of

dual purpose hemp crop a late flowering time could not leavenough time for seed ripening; there would be less time to preparehe soil for a subsequent winter cereal crop; late harvesting couldoincide with wet and cold periods that are not favourable for stemrying or homogenous retting.

Retting and subsequent mechanical processing to extract fibres particularly important for end-use destinations where clean fibres requested (Toonen et al., 2007). The selection of genotypes thatre easier to decorticate provides an advantage in terms of fibreuality and a reduction of costs related to fibre extraction (vanen Broeck et al., 2008), which seems to be the case for a cultivarecently released in The Netherlands (Toonen et al., 2004).

Considering that in Europe the cultivation of hemp as a dualurpose crop is prevalent, the choice of a specific variety should beriven by seed yield and specific seed oil characteristics. Faux et al.2013) pointed out that seed yield in dual purpose crops increasesith early sowing of early to mid-early cultivars and that femi-ized monoecious genotypes should be selected. Only few worksave studied the variability in terms of oil content and fatty acidomposition of hemp genotypes, or the effect of environment andultivation practices on the same traits (Kriese et al., 2004).

Among the multiple potential end-use applications of hemp, theery interesting secondary metabolites that can be extracted fromhe leaves and the inflorescence (Hazekamp et al., 2010) could stim-late, in the future, the selection of genotypes that could be grownor the fibre, for the seeds and for the essential oils or even for usefulannabinoids such as cannabidiol.

Even though the cultivation of hemp for cannabinoids is beyondhe scope of this work, it should be noted that the presence ofannabinoids, and namely of THC, in the top part of the plant has aery relevant influence on the choice of varieties for fibre and seedultivation. Only registered genotypes with a THC content lowerhan 0.2% can be used in industrial cultivation in Europe, while theame limit is 0.3% in China.

.3. Sowing time


Sowing date is usually defined on the basis of soil temperaturend water availability to guarantee a prompt germination and aapid crop establishment (Desanlis et al., 2013; Lisson et al., 2000a),nd on the basis of the photoperiod that defines the length of the

PRESSd Products xxx (2014) xxx–xxx 7

vegetative phase and ultimately stem and seed yield (Amaducciet al., 2008b, 2008d, 2012; Cosentino et al., 2012).

Generally early sowings correspond to higher stem and seedyields (Faux et al., 2013; Lu et al., 1963; Fang, 2010). In NorthernEurope time to reach 90% iPAR decreased when sowing passed frommiddle March to middle May, from 49 to 29 days, respectively (Vander Werf et al., 1996).

It should be noted, however, that in southern environments withearly sowings the crop can end the juvenile phase when the pho-toperiod is shorter than the critical one, which results in very shortvegetative growth (Amaducci et al., 2008b, 2008d, 2012; Cosentinoet al., 2012). At northern latitudes early sowings increase the riskof cold damage (Van der Werf et al., 1996).

Optimal sowing date for a specific environment not only posi-tively affects stem yields but may also lead to input savings. In aMediterranean environment, maximum stem yield was achievedwith a February or a March sowing but the earlier sowing resultedin a considerable saving of irrigation water, however dry stalk yielddecreased significantly (Di Bari et al., 2004).

In China hemp is planted in different climatic zones (coveringlatitude 23–50◦ N), with diverse soil types, cultivars, and rota-tion systems, as a consequence very contrasting sowing times arepracticed. Reasonably early sowing is preferred to elongate growthduration and increase yield (Lu et al., 1963; Fang, 2010), but delayedsowing decreases yield evidently (Liu et al., 2000b).

An interesting study on the effect of sowing date on fibre yieldand fibre extractability was accomplished by Westerhuis et al.(2009b), who evaluated the possibility to carry out late sowings,or even two hemp cultivations in the same year, in order to obtainshorter stems easier to harvest and process with available flaxmachineries.

3.4. Plant density

The response of hemp to varying planting density is a cleardemonstration of the plasticity of this species in adapting to crop-ping practice. Numerous authors report that the effect on biomassproduction is very limited within a wide range of planting densities(Westerhuis et al., 2009a; Amaducci et al., 2002b, 2008a). At higherplant populations canopy closure is faster, which is an advantage interms of competition with weeds (Lotz et al., 1991; Berger, 1969)and because maximum light interception is reached sooner witha consequent biomass yield advantage in the first growth phases(Amaducci et al., 2002b; Van der Werf et al., 1995b). This yieldadvantage is lost in the follow up of the growing season whenintense interplant competition at high seed densities resulting inself-thinning and biomass loss (Amaducci et al., 2002b; Grabowskaand Koziara, 2005; Van der Werf et al., 1995b). If the effect of seeddensity on stem yield is limited, it is very large the effect on stembiometrics, with plants grown at low densities that are usuallyhigher and have larger diameter compared to those grown at highdensity (Westerhuis et al., 2009a; Amaducci et al., 2002b, 2008a;Li et al., 2008; Grabowska and Koziara, 2005; Struik et al., 2000;Cromack, 1998; Van der Werf et al., 1995b). The influence of plantdensity on stem biometrics starts shortly after emergence, whenplants grown at high density are stimulated by light competitionto elongate, producing longer and thinner internodes. After this firstphase, competition limits stem growth, and internodes emission,so at the end of the vegetative phase plants grown at high densityare shorter, thinner and have less nodes (Amaducci et al., 2002b).

Stem height and stem diameter are relevant crop parametersthat interact with the harvesting system and mechanical process-


ing, especially when hemp is cultivated for the production of longfibres (Amaducci and Gusovious, 2010; Amaducci et al., 2008e;Venturi et al., 2007). Chen et al. (2004) found that maximum forceand energy required to cut hemp are higher than other fibre crops.


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han et al. (2010) found that compressing behaviours of hemptem is mainly affected by stem diameter and a higher energys required to process thicker stems. Considering that traditionalemp processing systems to obtain fibre ribbons suitable for longbre spinning, are very old and inefficient (Sponner et al., 2005),n innovative harvesting system was recently developed to adapthe hemp stems to modern flax scutching lines (Amaducci andusovious, 2010; Amaducci, 2003). With this system hemp stemsre cut and baled with the possibility to keep top and bottom por-ions separated. This could potentially improve fibre quality andomogeneity considering that finer and less lignified bast fibresre found in the top portion (Amaducci et al., 2005a, 2008a). Aemonstrative trial set up at industrial level failed to validate thisypothesis because of very high fibre loss measured on the top stemortion, that prove more difficult to decorticate and scutch due toheir small diameter (Amaducci et al., 2008e). Another unsuccessfultrategy to adapt hemp stems to modern flax scutching lines waseveloped in Italy in the beginning of the 21st century (Amaducci,005). Very dense hemp crops (up to 600 plants m−2) were killedith an herbicide when crop height was approximately 1.2 m and

herefore harvesting and subsequent processing was carried withax machines.

In addition to stem biometry, plant density affects fibre con-ent and fibre finesses and in general it is considered that atigher planting density correspond a higher yield of fibres (Vaner Werf et al., 1995b; Jakobey, 1965) that are finer (Khan et al.,010; Amaducci et al., 2002b, 2008a; Van der Werf et al., 1995b;akobey, 1965) and with a lower proportion of lignified secondaryast fibres (Amaducci et al., 2008b; Schäfer and Honermeier, 2006;an der Werf et al., 1994b). Other authors however found that theffect of planting density on stem fibre content was not signifi-ant (Jankauskiene and Gruzdeviene, 2013; Amaducci et al., 2008a;rabowska and Koziara, 2005; Höppner and Menge-Hartmann,995). Westerhuis et al. (2009a) in a recent study, where hemptems grown in Italy and the Netherlands at 3 sowing densities120, 240, 360 plants m−2) were divided in different portions, foundhat stem fibre content is almost completely determined by theeight and the position of the stem part. Since the weight of the

tem increased from beginning to end of flowering, also total fibreield and long fibre yield was maximized at later harvests. The effectf sowing density was limited and relevant only at early harvestingime, when fibre yield was higher at higher sowing density.

Very limited information is available on the effect of the culti-ation technique on fibre length. Considering that longer fibre isound in longer internodes (Kundu, 1942) it is assumed that sow-ng density could affect fibre length by influencing internode lengthAmaducci et al., 2002b).

The various seed rates suggested in literature for hemp planting,eflect on one side the lack of conclusive data on the effect of plantopulation on fibre yield and quality, but also the different end useestinations, harvesting methods, cultivar type and soil conditions.

The optimal density for the cultivation of drug hemp seemso be 10 plants m−2 (Rosenthal, 1987); Meier and Mediavilla1998) found that highest yield of inflorescence was obtained at5 plants m−2 and assume that maximum essential oil produc-ion would be at the same plant density; for seed productionptimal density varies from 30 to 75 plants m−2 (Venturi, 1965;ennink et al., 1994; Van der Werf, 1994); the largest variationas found for fibre production with sowing densities ranging from

0 to 750 plants m−2 (Dempsey, 1975), with higher rates suggestedor textile destinations (150–200 plants m−2 Jaranowska, 1966;50–350 plants m−2 Starcevic, 1996) and lower for non-textile des-


inations, e.g. 90 plants m−2 for paper pulp (Martinov et al., 1996).n Italy dioecious varieties for textile destination were traditionallylanted with a target of 90–100 plants m−2 (Bruna, 1955; Venturi,967; Venturi and Amaducci, 1999). In China, stem, fibre and/or


bast yield were maximized at plant density of 120–150 plants m−2

(Fang, 2010; Li et al., 2008; Liu et al., 1991).

3.5. Plant nutrition

The major role that nitrogen (N) plays in crop nutrition also inhemp is well represented by the relatively large number of articlesthat have addressed the effect of this nutrient on hemp productivity(Table 4).

Experimental results confirm that nitrogen fertilization shouldbe determined on the basis of soil fertility, in fact the yield responseof hemp to supplemental nitrogen was negligible in rich soils (Pradeet al., 2011; Struik et al., 2000) while significant yield increaseswere reported in nitrogen limiting conditions (Finnan and Burke,2013b; Vera et al., 2010; Amaducci et al., 2002a; Struik et al., 2000;Ivonyi et al., 1997; Van der Werf et al., 1995c). The increase of stembiomass per unit of nitrogen fertilization cannot be uniquely deter-mined from literature data due to very contrasting environmentalconditions and to the different methodology used to calculate nitro-gen availability for the crops. A low stem yield increase (∼8 kg ofstem DM increase per kg of N applied) was reported by Van derWerf et al. (1995c) passing from 80 to 200 kg of available soil N inthe Netherlands, while a slightly higher yield increase was reportedby Song et al. (2012) with N fertilization from 0 to 90 kg ha−1 in Hei-longjiang Province, China (∼12 kg stem DM per kg of N). A very highstem yield increase (as high as 60 kg of stem DM per kg of N) wasreported by Finnan and Burke (2013b) increasing nitrogen fertiliza-tion from 0 up to 120 kg N ha−1, while no further yield increase wasmeasured with 150 kg ha−1. Intermediate stem biomass increase(20 kg of stem DM per kg of N) were reported by Struik et al. (2000)passing from 100 to 220 of available soil N in the Netherlands andUK and by Amaducci et al. (2002a) increasing nitrogen fertiliza-tion from 0 up to 120 kg N ha−1. Similar intermediate stem biomassincrease was also found in a recent study in Canada (Vera et al.,2010).

In most of the field experiments nitrogen was applied at sowing,but, as reported by Finnan and Burke (2013b) nitrogen distributionafter sowing or in split applications did not increase stem yieldcompared to distribution at sowing.

Ivonyi et al. (1997) found the phase of intense N accumula-tion started one month after sowing and lasted approximately onemonth. By the end of this phase, 79% of total N uptake had occurredwith daily N uptake of 3–4 kg ha−1.

Excessive nitrogen fertilization, stimulating very fast stemelongation, renders the hemp crop more susceptible to lodging(Desanlis et al., 2013).

Bócsa et al. (1997) reported that high nitrogen fertilizationreduced the THC content in leaves, in accordance with Wu et al.(2010), who showed that N fertilizer and other cultivation prac-tices (e.g. increased planting density, postponed sowing time andshading) decreased THC contents in three hemp varieties.

Hemp is less responsive to potassium (K) and phosphorous (P)than to N fertilization. Finnan and Burke (2013a) found no corre-lation between hemp yield and either K rate or the level of K inthe soil. The authors concluded that hemp has a lower requirementfor K than other crops, and they suggest an annual requirementof 65 kg ha−1. Luxury uptake has been observed (like with grasses)with a high K level in the soil. Late maturity varieties uptake moreK than earlier ones, with most of the adsorbed K concentrated inthe stems (70–75%).


Limited research has been carried out on the effect of P on hempproduction. Ivonyi et al. (1997) reported that P fertilization didnot affect stem yield, and P uptake by the crop ranged from 52to 67 kg ha−1.



ARTICLE ING ModelINDCRO-7384; No. of Pages 15

S. Amaducci et al. / Industrial Crops an

Tab

le

4H

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atio

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rate

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P

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K

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Tot.

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ld

(t

DM

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)

Ref

eren

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Feri

mon

12, F

elin

a

32, F

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ra

75,

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035

150

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nan

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(201

3b)

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on

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20

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50–

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3b)

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74, F

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omp

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uri

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p, p

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izat

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5

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2000

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uri

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den

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ion

UK

100–

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al. (

2000

)

–

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n

and

row

wid

thTh

e

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her

lan

ds

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3

(ste

m

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d)

Van

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f et

al. (

1995

b)Fe

lin

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Kom

pol

tiN

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atio

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pla

nt

den

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y

100–

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2002

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0–90

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2012

)Lo

ng

Hem

p

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Relatively limited information is available on the effect ofplant nutrition on plant quality characteristics. Van der Werfet al. (1995c) found that the proportion of bark on the stemwas lower at higher soil nitrogen levels and reported that sim-ilar results had been found in other studies (Jaranowska, 1964;Rivoira and Marras, 1975). Legros et al. (2013) reported thatwith high nitrogen fertilization stems remain green for a longertime and this interferes negatively with mechanical fibre separa-tion.

Jordan et al. (1946) reports that high nitrogen doses resultin higher fibre yield but also in lower fibre strength. Grabowskaand Koziara (2005) state that with high nitrogen doses vegetativegrowth is stimulated, while fibre content and fibre strength aredepressed. The cell fibres grown at high nitrogen rate have a largerlumen and therefore lower technical characteristics. Malceva et al.(2011) reported that fibre content tented to decrease with additionof nitrogen fertilizer, seed yield increased and oil contented tendedto decrease. However, all this parameters were strongly influencedby the year of cultivation.

3.6. Role of hemp in the crop rotations and weed management

Hemp is a typical break, spring-summer crop that has a veryimportant position in crop rotations because of its beneficial effecton following crops (Venturi and Amaducci, 1999). Wheat yieldin particular seems to benefit when hemp was grown as preced-ing crop (Gorchs et al., 2000; Bócsa and Karus, 1998). In a recentfield trial Liu et al. (2012) have proven that hemp has a posi-tive effect also as preceding crop of soybean, in conditions wheresoybean is grown as monoculture. Cultivation of hemp in mono-culture might cause a rapid decrease in fibre yield as shown byLi (1982). This could be the consequence of pathogens; it is infact advisable to avoid in the same rotation with hemp speciesthat are susceptible to Pythium, Sclerotina and Piralide (Rivora,2001).

Its fast growth after emergence renders hemp very competitiveagainst weeds (Lotz et al., 1991; Berger, 1969), and weed controlis usually not necessary, making hemp an ideal crop for organicagriculture (Stickland, 1995).

In China, however, hand or chemical weeding is carried outwhen necessary. Especially in Southern China, chemical weedmanagement is preferred. Herbicides are spread on the soilafter sowing and before seedling emergence. Song (2012) recom-mended 65% metolachlor emulsion (3 L ha−1) or 30% pendimethalinEc (3 L ha−1) as enclosed treatment chemicals in HeilongjiangProvince, China. Liu et al. (2010) suggested 96% metolachlor Ec1050 mL ha−1 or 50% acetochlor Ec 750 mL ha−1 as the herbi-cides for the hemp field, based on their experiment in HunanProvince, China. Furthermore, Liu et al. (2005) reported 50%acetochlor Ec 2250 g ha−1 for weeding in Yunnan Province,China.

Hemp has proved to be highly sensitive to the residue of herbi-cides in the soil, therefore it is advisable to avoid the cultivationafter maize if atrazine and simazine are used, or after tomatotreated with specific herbicides for Solanaceae.

It is considered that its deep root system improves soil structure(Amaducci et al., 2008c).

Hemp cultivation is often followed by a winter cereal, it istherefore important, especially on difficult soils, that harvestingis carried out early enough not to delay soil preparation. This is inline with the suggestion of some authors that optimization of fibre


production should be achieved with early sowings coupled to earlyharvests, so to avoid unfavourable conditions for retting and stemdrying (Höppner and Menge-Hartmann, 2007; Müssig and Martens,2003).


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0 S. Amaducci et al. / Industrial Cr

.7. Irrigation, how the availability of water affects yield anduality

Drought in combination with high temperature has beeneported to accelerate flowering development (Amaducci et al.,008b; Heslop-Harrison and Heslop-Harrison, 1969) but to delaylant growth and fibre maturation (Abot et al., 2013). Schäfer andonermeier (2006) report than in a two years experiment stemeight, stem diameter were lower and layers of fibres thinner inhe year with drier conditions.

Studies in Europe indicate that hemp requires 500–700 mm ofvailable moisture for optimum yield, and that 250–300 mm ofoisture should be available during the vegetative growth stage

Bócsa and Karus, 1998).In China, hemp is usually planted in hillside lands in rainfed

ondition. Liu et al. (2013, not published) observed negative effectshen manpower watering after sowing hemp field resulted inneven seedling emergence and stunt of seedlings.

Information regarding hemp irrigation is available only fromtudies carried out in Southern European environments character-zed by prolonged water deficit where most species are successfullyultivated only with the use of irrigation.

Cosentino et al. (2012) conducted a study with different sowingates and various levels of water availability. Postponing sowingate reduced the water needed by the crop, because unfavourablehotoperiodic conditions considerably reduced vegetative growth.

These results were corroborated by another study conductedn the same environment with several monoecious and dioeciousarieties. It was concluded that at least 250 mm of irrigation wateror monoecious early genotypes and 450 mm for dioecious lateenotypes are needed in semi-arid Mediterranean environmentCosentino et al., 2013).

In the same environment the variety Futura 75 did not showignificant yield reduction when irrigation was reduced from 100%Tm to 50% ETm restitution while statistical yield reduction washown with stressed and severe stressed treatment (25% ETm resti-ution and irrigation until crop establishment, respectively).

In a similar environment of Southern Europe, Di Bari et al. (2004)ested four irrigation regimes (from 680 mm to 262 mm of irrigationater) and found that the hemp crops showed good yields in terms

f stems and dry bark when 66% of the available water was restored,orresponding to a seasonal water consumption of 410–460 mm Inhe best water condition, hemp reached the maximum values ofT (6 mm d−1) two months after sowing, and maintained it in theottest months of the year, until harvest.

In environments with high evapotraspirative demand (as thease of South Mediterranean environment), water consumptionanges between 250 and 450 mm while water consumption is lowernd varies between 200 and 300 mm in North Mediterranean envi-onments (Rivoira and Marras, 1975; Amaducci et al., 2000).

.8. Harvesting time as a function of end use destinationfibre + seed)

A large number of scientific publications have studied the effectf different harvesting time on fibre yield and fibre characteris-ics. Traditionally hemp for fibre production was harvested at fullowering of male plants (Bócsa and Karus, 1998), when primaryast fibre yield reaches its maximum (Westerhuis et al., 2009a;maducci et al., 2008b; Mediavilla et al., 2001).

Liu et al. (2012, not published) showed that delayed harvestsncreased the yield of biomass and stem, but caused a relative


ecrease of bast ribbon yield (Table 5). When hemp was harvestedt five days interval between 60 and 100 days after emergencefrom flower buds appearance to end-flowering stage), in Hei-ongjiang Province (China), average bast fibre content was between


15.8% and 22.3% at 60 and 90 days after emergence, respectively,reducing to 19.2% at the latest harvest time (Zheng et al., 2013).

In accordance with other studies, primary bast fibre contenttends to decrease along the cropping cycle and after flowering,due to continuous accumulation of secondary fibres and xylem(Amaducci et al., 2008b; Keller et al., 2001; Mediavilla et al., 2001).Postponing harvesting time until seed maturity, as in dual purposehemp crops, results in a higher proportion of lignified fibre. Kelleret al. (2001) reported that delaying harvesting after the end of flow-ering resulted in improved decorticability of the stem, which is ofcourse a positive factor. Xu et al. (1989) tested the structure quali-ties (including optical orientation factor f0 and crystallinity index)of fibre hemp harvested from very early to very late stage in Shan-dong Province, China. Results showed that the most suitable timefor hemp harvest was five days before and after June 30 (full-bloomstage); beyond that range lower fibre quality was observed, andanticipated harvests were worse than delayed ones.

Amaducci et al. (2008b) found that fibre yield increased by 25%between beginning and full flowering mainly because of fibre mat-uration at higher internodes was more advanced: it is thereforeconcluded that time of harvesting should be set at full flowering tomaximize fibre yield but also fibre homogeneity. Furthermore, toestablish beginning of flowering for harvesting can be misleadingbecause of “pre-flowering” in unfavourable environmental condi-tions and in certain genotypes (Amaducci et al., 2008d; Cosentinoet al., 2012).

Considering that harvesting time is set on the basis of plantphenology, in a specific environment harvesting time could beprogrammed by choosing a genotype with specific photoperiodsensitivity. When dew retting is carried out, harvesting should takeplace when there is a high probability to find suitable weather con-ditions. In Northern and humid climates delaying harvest until theend of summer might result in lower fibre yield and worse qualitydue to excessive rain (Bennet et al., 2006), while the opposite mightbe true for Southern and dry conditions where harvesting late, incoincidence with late summer rains, would favour field retting.

When hemp is cultivated for pulp and paper and for bioenergydestinations, harvesting time has a relatively limited influence onbiomass characteristics, and late harvests should be preferred tomaximize biomass production (Godin et al., 2013; Kreuger et al.,2011; Kamat et al., 2002). Prade et al. (2011) reported that opti-mal harvesting time for biogas production falls in September andOctober when there is a long period without major variations ofbiomass quality and good conditions for harvesting are usuallyfound. Spring harvest can be preferred when hemp biomass isused for solid fuels because hemp biomass dries during the win-ter months (down to 20–30% of moisture content), however, somebiomass is also lost. Prade et al. (2011) found that the drawbackof biomass loss and the advantage of having dried biomass afterthe winter compensate each other and it is therefore irrelevant toharvest in autumn or spring from an energetic point of view, whileKolaricova et al. (2013) reported that the energy return was higherfor the spring harvest.

4. Actual hemp cultivation and future perspectives

4.1. Hemp cultivation in Europe

Once a very important industrial crop, hemp decline after IIWorld War has been unstoppable and at the end of the 1960s ithad almost disappeared from most of the Western European coun-


tries. A renewed interest on hemp cultivation started in the early1990s when the cultivation of hemp was reauthorized throughoutthe European Union. After more than 20 years hemp is still a nichecrop, cultivated on 10,000–15,000 ha in the European Union (Carus



S. Amaducci et al. / Industrial Crops and Products xxx (2014) xxx–xxx 11

Table 5Harvest time and hemp yield (t DM ha−1).

Country Harvest date Biomass yield(t ha−1)

Stem yield (t ha−1) Bast yield (kg ha−1) Reference

Kunming, China

September 19 9.9 6.6 988.1Liu et al. (2012, notpublished)

September 29 12.3 8.2 1240.1October 9 16.2 10.6 1545.6October 19 16.7 10.9 1511.9

South ItalyJune 23 (Beginning flowering) 6.7 4.6 –

Cosentino et al. (2013)July 13 (End flowering) 10.6 7.6 –

August 18 (Beginning flowering) – 4.1–6.0 –

eikgftcttfia2low

tm

lydrssrrio4biNmFgote

iilsirstpvs

North United kingdom September 1 (Middle Flowering) –

September 15 (End flowering) –

t al., 2013). In the last 30 years, France has been the leading countryn Europe for the cultivation of hemp and a relatively stable mar-et for the hemp products has favoured the development of newenotypes and cultivation systems. The main end use destinationor hemp in France is the production of specialty papers, for whichhe level of purity (defined as the percentage of woody core on theommercial fibre) is quite high and up to 35% of shives attached tohe fibres are acceptable (Bouloc, 2013). Other industrial destina-ions require a higher degree of purity, 2% in the case of technicalbre (i.e. insulation materials, biocomposites) while no shives arecceptable when the fibre is used for textile applications (Bouloc,013). The high level of shives attached to the fibre and a relatively

ow price paid for the raw material, have stimulates the selectionf varieties and the development of a cultivation technique thatould maximize stem yield.

Legros et al. (2013) summarized the results of long term fieldrials carried out in France, in particular examining the effect of the

ain agronomic factors on stem, seeds and fibre yield.Highest fibre yield is obtained from late cultivars that have

ong vegetative growth, while early cultivars have the highest seedields. Considering that stem and fibre yield is determined by theuration of the vegetative phase, a delay in sowing time alwaysesults in a yield reduction. Sowing should therefore take place asoon as the soil temperature exceeds 8 ◦C. A drawback of exces-ively early sowings can be the very prolonged flowering time thatesults in inhomogeneous seed maturation. Sowing density is a veryelevant factor for the production of both fibre and seeds. Fibre yieldncreases with seeding density but relatively high fibre yields arebtained with 150–200 plants m−2 at emergence (or approximately0–45 kg ha−1 seeding rate). This seeding density represents theest compromise between fibre and seed production, consider-

ng that seed production decreases at increasing planting density.itrogen fertilization from 50 to 100 kg ha−1 satisfy crop require-ents and guarantee maximum yields in most field conditions.

ibre processing is easier with higher seeding densities, low nitro-en fertilization and late harvesting, while minimal is the influencef the genotype. The most influential factor, however, is rettingime: increasing retting times (up to 5–7 weeks) facilitate fibrextraction.

While achieving a clean fibre is of limited relevance when aim-ng at the paper and pulp market, this is very important for thencreasingly interesting applications in the biocomposite and insu-ation sectors or for high value textiles. The cultivation techniqueshould be optimized and the commercial genotypes should bemproved to bring high quality hemp fibre onto the market. Theelatively low price paid for the fibre and the competition fromupported bioenergy crops (Carus et al., 2013) further complicates


he situation. Traditionally, high quality fibre was obtained fromlants harvested at flowering, while today the crops must be har-ested at seed maturity to benefit from the additional income fromeed sale.

Bennet et al. (2006)3.0–5.0 –3.3–6.5 –

The call for new genotypes and an improved crop management,that coupled to a suitable mechanization and processing systemcan lead to the production of high yield of fibres of defined qualityand seeds, is perfectly in line with the principles of the modernbioeconomy.

4.2. Hemp cultivation in China

China has traditionally cultivated hemp for fibre and seed formore than 6000 years. Its cultivation reached a peak and pros-perous period from Hang to Tang Dynasty in ancient China (Yang,1991). Some practices and experience of cultivation in those dayswere recorded in a lot of ancient Chinese documents. In the late1970s and the early 1980s, the average fibre hemp planting areaonce reached about 160,000 ha Nowadays, China is one of the mostimportant producers of industrial hemp, with a yearly harvestedarea of 12,130 ha (47.8% of the world total) for fibre hemp and12,809 ha (40.5% of the world total) for seed hemp in the last decade(FAOstat, 2013). At present, the main end use destination of fibrehemp in China is for the production of textile fibre, while the seedis mainly for the food industry. Most fibre hemp is cultivated in theNorth-eastern, Central-eastern and South-western parts of China,while hemp seed production in carried out in Northern China.

Hemp growing conditions in the North (Heilongjiang Provinceas an example) and South (Yunnan Province) part of China areextremely different due to contrasting climates, especially the day-length variation pattern, but also farm structure and managementtechniques vary. Mechanization is widespread in the large and flatfarms of Northern China, while in mountainous areas of SouthernChina most field operations are carried out by hand. The amount ofbasal fertilizer and top dressing are not significantly different, butthe N:P2O5:K2O ratio for northern and southern China is 5:3:4 and4:2:3 for basal fertilizer, and only 1.3:0:1 for top dressing.

A rate of N 37.5 + P2O5 56.3 + K2O 37.5 kg ha−1 was suggested byFang (2010) for hemp in Northern China, while Song et al. (2012)recommended N 90.0 + P2O5 100.0 + K2O 80.0 kg ha−1 for hemp pro-duction in Heilongjiang Province.

For cultivation as a dual purpose crop (both seed and stalk), theoptimized ratio of N:P:K is considered to be 2.0–2.4:1.0:1.6 (Guoet al., 2011).

The hemp cultivars for Northern China were mainly introducedfrom Ukraine, for example Dnepr 6 and Golden Knife 15, but thereare also varieties from other European countries, as well as localvarieties originating from the high latitude areas. By contrast, thecultivars used in Southern China are home bred cultivars such asYunMa 1, YunMa 3 and YunMa 5; local cultivars are seldom used.Sowing times for industrial hemp in Northern China are from April


10th to May 10th, 60–105 kg seeds per hectare, with a popula-tion of 80–500 plants m−2, while in Southern China hemp is sownfrom March 10th to the end of May, 30–45 kg seeds per hectare,with a smaller population 22–150 plants m−2. The main diseases,


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ests and weeds in hemp fields in Northern and Southern Chinare not remarkably different, and the control measures are theame, i.e. agricultural control such as crop rotation, physical controluch as light trap, biological control such as trichogrammatid fortem borer, as well as chemical control. Industrial hemp in North-rn China is harvested at late flowering stage of male plants – theechnical maturity – 110–120 days after sowing, i.e. from late Julyo middle August. However, in Southern China hemp is harvestedt full-blooming stage of male plants – the technical maturity –0–100 days after sowing, i.e. from middle to late August. For thearvest method of industrial hemp, in the Northern part of China,tems are cut at the bottom, dew retted in the fields, peeled byachine or manpower, or scutched with a machine; in the South-

rn part of China, stems are cut, top branches and leaves removed,raded by diameter, decorticated with a small machines (by decor-icating fresh stem method) in the field or peeled manually on around nearby the house. Thus mechanized farming and a cultiva-ion managing system of less labour cost will be the main directionf the development for hemp production in the future. Ten yearsgo local farmers cultivated hemp by their traditional agronomicractices and small scale planting for each farmer or producer.s a result, the yield and quality of hemp were very different

hroughout the country. With the development of Chinese agri-ultural industrialization and large scale production on hemp, theultivation techniques and strategies in the future should be moretandardized. Due to the large planting range (from 23◦ N to 50◦

) and the increasing development of different end uses, differentenotypes are needed in China. Accordingly, precision cultivationechniques that target the corresponding genotypes and main pro-ucing regions (the South and the North) in the hemp productionhould be developed further.

. Conclusion

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

A relatively large scientific literature dealing with the effectf environment and cultivation practices on hemp production isvailable, while limited information is available on the effect ofnvironment and management on plant quality characteristics (ofbre, seed and secondary metabolites). Evaluation of commercialarieties on the basis of their suitability to different end use appli-ation is also lacking.

In the short term, a significant improvement of hemp productsnd broader end use applications are expected if future researchill address the abovementioned, agronomic issues. However,

he full potential of hemp will be attained when the genes thatontribute to the plant’s quality characteristics will have beendentified, and this knowledge will have been exploited in theevelopment of varieties tailored to specific end-uses.

cknowledgements

This work was supported by FIBRA project (Fibre Crops as austainable Source of Bio-based Materials for Industrial Productsn Europe and China), funded by the EU Seventh Framework Pro-ramme under the Grant Agreement 311965.

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