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The influence of changing sowing rate and harvest time on yield and quality for the dual use of fibres and seeds of hemp (Cannabis sativa L.)

Frank Hppner, Ute Menge-Hartmann and Jrg Michael Greef

Institute of Crop and Grassland Science; Federal Agricultural Research Centre, Bundesallee 50, 38116 Braunschweig,
Germany,, Email


Hemp cultivation could be more economically attractive for farmers of the European Union if both hemp stems and hemp seeds were to be harvested. Therefore, the early maturing hemp cultivars Fasamo (Germany) and Juso31 (Ukraine) were tested on loamy sand at the FAL in Braunschweig-Vlkenrode. Both cultivars were sown at two different sowing rates (45 and 20 kg/ha). Harvest time was varied with an emphasis on predominant fibre production (harvest time: initial start of seed maturity) or predominant seed production (harvest time: seed maturity). From the initial start of seed maturity to seed maturity, a decrease from 83.9 to 75.9 dt/ha in stem yield was observed. But this observation caused no great effect on fibre yield (from 27.6 to 25.1 dt/ha). Seed yield, however, was increased enormously from 295.9 to 1261.3 kg/ha. Fibre quality parameters like fibre filling and fibre strength had predominantly improved. An increase of secondary fibres was really unwanted but cannot be prevented. A reduction is possible by using cultivars with less enrichment of secondary fibres. Both cultivars were suited for dual use as fibres and seeds. The cultivar Fasamo reached slightly higher seed yields.

Media Summary

The hemp cultivars Fasamo and Juso31 were tested for dual use as fibres and seeds at two different sowing rates of plant density and for two different production goals.

Key Words

Hemp fibre, Hemp seeds, Primary and secondary fibre


Since 1996, farmers have been allowed to cultivate hemp in Germany and other European countries. Farmers took stock in hemp cultivation because they received high area subsidies from the Commission of the European Union. Subsequently a fibre extracting factory was built. Up until that time only minimal knowledge was available on different cultivars of hemp. Hemp is a relatively late maturing species, particularly in northern Germany. Thus, first research was conducted with varieties from different regions to find early maturing cultivars with high dry matter yield and high fibre content (Buttlar von et al. 1997, Hppner and Menge-Hartmann 2000). Today, the subsidies are lower than in 1996 and divided into two parts: area subsidies for cultivation (for farmers) and fibre subsidies (for fibre extracting factories). Fibres have to be extracted from stems in order to receive a subsidy. As a result of the lower subsidies for farmers, the cultivation of hemp could be more economically attractive if both hemp stems and hemp seeds were to be harvested. A specialty market exists for peeled hemp seeds and hemp oil as a raw material for the food, pharmaceutical, and cosmetic industries. In the fatty acid composition of the oil a low level of linolenic acid was detected. This acid contains the meaningful γ-linolenic acid, a substance physically important for humans. Therefore farmers could have additional interest in the coupled production of fibres and seeds, but then with an emphasis on higher seed yields. For this production aim only early maturing hemp cultivars and lower seed rates seem to be suitable. Therefore the efficiency of two early maturing monoecious cultivars was tested for predominant seed production in comparison to predominant fibre production.


Field experiments were carried out in four replications (block design) on loamy sand at the FAL in Braunschweig-Vlkenrode from 1999 to 2001 (∅ 620 mm precipitation, 8.9 C average temperature).

Following preconditions were given:

  • Cultivars - Fasamo, Juso31
  • Previous crop: - White lupin
  • Sowing date :- End of April/beginning of May
  • Sowing rate: - 45kg/ha for predominant fibre production and 20kg/ha for predominant seed production (minimum sowing rate to receive subsidies)
  • Nitrogen fertilisation: - 80 kg/ha
  • Base fertilisation: - 70 kg/ha P2O5, 140 kg/ha K2O, 21 kg/ha MgO

Seeds were drilled with a precision seed drill. A plot consisted of 10 rows with a row width of 12.5 cm. A harvest took place at two stages:

  • Predominant fibre production - initial start of seed maturity (“technically ripe fibres”)
  • Predominant seed production - seed maturity (more than 50 % of seeds/plant are capable of being threshed)

The fibre content was determined by mechanical decortication. The specific strength of green bark stripes of the stem middle (mod. after Heyland und Kromer, 1995) was determined. The degree of primary fibre filling at cross sections of the stem middle was rated, Valuation: 1 = all fibres are well filled, 2 = 66% of fibres are well filled, 3 = 50% fibres are well filled, .....6 = all fibres are poorly filled (bad).


Seedling emergence of the hemp cultivars started about one week after sowing. At first, growth was rather slow, but the hemp had a strong growing phase, especially in the months June and July. The intensive growth in length stopped with the start of the flowering stage. Hemp, as a short day plant, shifted from vegetative to regenerative growth when the days became shorter. Both cultivars showed no difference in the onset of their flowering, both reacted early in July (Buttlar von et al. 1997, Hppner and Menge-Hartmann 2000).

One result of different sowing rates on the plant density was a difference of 100 plants at time of harvest. Plant density in fibre production was 211 plants/m2 and in seed production 116 plants/m2.

Stem length of the plants lay between 150 and 170 cm, thickness between 5.4 and 6.3 mm (Table 1). The highest value of stem diameter was achieved by the plants predominantly for seed production. Two effects led to significantly higher plant heights and thicker stems: the lower plant density resulted in less competition for light, nutrients and water, the regenerative part of the plants had a longer growth phase (Hppner 1997, Hppner und Menge-Hartmann 2002). In addition, the nitrogen supply and rainfall during the vegetation period influenced stem length and thickness (Hppner und Menge-Hartmann 1995). The cultivar Juso31 achieved longer, thicker stems than Fasamo. But the higher stem thickness should not lead to problems for fibre extraction because other cultivars had a priori thicker stems (Hppner and Menge-Hartmann 2000).

Table 1. Effects of two cultivation systems on growth and yield parameters of two hemp cultivars in two cultivation systems (∅ 1999-2001)

Cultivation sytem









Predominant fibre production


150.3 a

4.6 a

80.6 ab

25.2 a

23.9 a

304.0 a

25.3 a

77.0 a


155.9 ab

5.4 b

88.9 a

33.9 c

33.3 b

286.2 a

23.1 a

73.0 a

Predominant seed production


162.9 ab

5.3 b

74.3 b

27.9 b

23.2 a

1402.2 b

34.8 b

489.2 b


170.3 b

6.3 c

76.6 ab

31.2 c

27.9 a

1120.4 b

34.7 b

392.6 b

Predominant fibre production

152.2 a

4.9 a

83.9 a

28.7 a

27.6 a

295.9 a

24.2 a

75.2 a

Predominant seed production

166.6 b

5.8 b

75.2 b

29.9 a

25.1 a

1261.3 b

34.8 b

440.9 b

different letters indicate significance (p < 0.05; Tukey-Test)

Stem dry matter yield lay between 74.8 and 88.9 dt/ha (Table 1). Highest yields were achieved in predominant fibre production. The lower plant density for predominant seed production significantly decreased stem yield. Juso31 achieved a slightly higher yield in comparison to Fasamo, because of its longer and thicker stems. The effects of the cultivation system on fibre yields were lower. The higher yield of 2.5 dt/ha in predominant fibre production was not significant, because the fibre content in predominant seed production was slightly increased (Table1). Juso31 achieved a higher fibre content and fibre yield than Fasamo, especially in predominant fibre production. This was also mentioned in investigations by Hppner and Menge-Hartmann (2000).

The later harvest in predominant seed production significantly increased seed yield, oil content and oil yield. Because an individual seed had a higher mass, more seeds were established and their degree of maturity reached a better level in contrast to predominant fibre production (Table 1). In other studies it was reported that sowing rate had only little effect on seed yield (Hppner 1997). Similar seed yield values could be reached with a plant density for fibre hemp cultivation when harvest took place at seed maturity (Hppner 1995). Highest yields of seeds and oil were observed particularly for the cultivar Fasamo in predominant seed production, but the differences were not significant. Both cultivars nearly reached the same level of oil content. Subsequently the disadvantage of Fasamo in terms of seed yield did not lead to a benefit in oil yield as compared to Juso31. The oil contained the main fatty acids linolic-, linolenic- and oil acid in a concentration sum of more than 80%. The meaningful γ-linolenic acid reaches highest values from early maturing cultivars and concentrations are higher when seeds are immature (Hppner and Menge-Hartmann 2000). In this study the concentration of γ-linolenic acid was also decreased significantly from 3.8 to 3.2% at a later harvest date.

The structure of the hemp stem is of interest as a quality parameter. Fibres could be differentiated as primary (long) and secondary (short) fibres. Juso31 had a significantly higher layer number of primary fibres and a significant higher layer thickness in comparison to Fasamo (Table 2). The layer thickness of primary fibres decreased with predominant seed production. Secondary fibres were initially developed later during vegetation period and depended on cultivars, nitrogen supply, plant density and water (Menge-Hartmann und Hppner 1995, Hppner und Menge-Hartmann 2002). Fasamo and Juso31 belong to the cultivars with lower amounts of secondary fibres (Hppner and Menge-Hartmann 2000). A maximum of 29.6% of Fasamo plants accumulated secondary fibres in predominant seed production when the plant density was lower (Table 2). An increase in secondary fibres could mean that a portion of the fibre content should be secondary fibres, which could explain why the fibre content with predominant seed production did not strongly decrease.

Table 2. Influence of two cultivation systems on quality parameters of two hemp cultivars at two cultivation systems (∅ 1999-2001)

Cultivation sytem

Primary fibre layer number

Primary fibre layer thickness

Plants with secondary fibres

Primary fibre filling

Specific strength

Predominant fibre production


6.3 a

139.8 a

0.0 a

2.1 a

57.7 a


7.9 b

181.8 b

14.6 ab

3.3 b

59.0 a

Predominant seed production


6.6 a

125.7 c

29.6 b

1.6 a

65.2 a


7.7 b

154.3 d

15.2 ab

3.4 b

70.2 a

Predominant fibre production

7.1 a

162.2 a

7.8 a

2.7 a

58.3 a

Predominant seed production

7.0 a

136.8 b

23.8 b

2.3 a

67.7 b

different letters indicate significance (p < 0.05; Tukey-Test)

Other quality parameters are the degree of fibre filling of primary fibres and the specific strength. Best results in the degree of fibre filling were achieved by Fasamo with a score of 1.6 in predominant seed production (Table 2). In a comparison of the two harvest times, most cultivars showed an improvement in fibre filling when they were harvested later (Menge-Hartmann und Hppner 1996, Hppner and Menge-Hartmann, 1999). Highest values in specific strength were achieved by Juso31. Both parameters had a high relation to a cultivar (Hppner and Menge-Hartmann 2000, Sankari 2000). But the cultivation method also significantly influenced the value of fibre strength (Table 2) (Hppner und Menge-Hartmann 1995).


Under the aspect of dual use of fibres and seeds, farmers could produce hemp in two different cultivation systems: either with a main emphasis on fibre production or main emphasis on seed production. Before seeding farmers have to come to a decision about sowing rate. If the main emphasis is on seed production, farmers should reduce the sowing rate to have lower seed costs. The cultivation of Fasamo tends to result in higher seed yield. At the same time, the coupled product fibre neither produces lower yields nor losses quality. But fibre quality is difficult to determine. The question is the purpose for which the fibres will be used. Slight differences in the quality of short fibres are not critical for a lot of applications. In northern Germany, the late harvest time at seed maturity could be a problem for the storage moisture of seeds and straw. Consequently harvest should be carried out a little earlier.


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