Hemp (Cannabis sativa L.) production and uses in Ireland

J. Crowley and B. Rice

Teagasc - Crops Research Centre, Oak Park, Carlow, Ireland

     Historical records indicate that hemp was grown in Ireland during the 18th century, but no commercial enterprise was established. Some hemp was grown during the 1938-45 period for bird seed. The first scientific evaluation of hemp took place from 1960-66, using the varieties Fibrimon 21, 24 and 56. Stem yields of 10 t/ha and fiber yields of 2.5 t/ha were achieved. The quality of yarns and twines produced were shown to be slightly inferior to British Standard specifications. It was concluded that, at the prices then prevailing, hemp could not be regarded as an economic source of raw material for paper manufacture (Neenan 1969).
        As with most European countries, the search for alternative non-food crops has been underway in Ireland since the late 1980ís. The high yields and long list of possible industrial uses for hemp (Herer 1995) prompted a limited re-examination of the crop in Ireland starting in 1995.
        Two objectives were set in this re-evaluation: (a) to establish the yield potential of the low-THC varieties and (b) to identify possible domestic end-users. With no paper industry in Ireland, two optional uses for the whole unprocessed stem were considered: (a) burning to generate energy and (b) fiber board manufacture. Either option would require a large production area to achieve economic viability. If this were established, it could serve as a stepping stone towards constructing a fiber extraction facility.

Renewable energies in Ireland
     Ireland has been a late starter in promoting renewable energy technologies. There are no environmental or CO2 taxes to stimulate renewable energy development. Since 1995, an Alternative Electricity Requirement (AER) scheme has been operated by the Electricity Supply Board (the national procurer) in which enhanced prices were paid for electricity generated from renewable sources. Three rounds of this scheme have now been completed. The successful tenders have been mainly for a wind plant, with a number of land-fill and hydro projects, one 30 megawatt (MW) municipal waste-to-energy plant and only one small biomass (biogas) project. In the most recent round of tenders, wind-power has been offered at very competitive prices, between 2 and 3 pence per kilowatt-hour (kWh). This is likely to depress the prices offered for electricity from biomass projects in future rounds.

Energy from biomass
     Only about 1% (5 petajoules) of Irelandís primary energy demand comes from biomass at present. This is mainly wood-waste used for home heating and industrial drying in the wood processing industries. Raw material procurement is the predominant cost component in all biomass-to-energy systems. To produce energy at a cost approaching that of conventional mineral fuels, stable supplies of low-cost raw materials are essential. At present, these are most likely to be residues or wastes for which competing uses are either low-value or non-existent (Rice et al.. 1997).
        Opportunities for the use of arable crops as fuels have been virtually ruled out at present by reductions in set-aside land and uncertainty surrounding its future. The ĎAgenda 2000í proposals now taking shape may well offer somewhat better prospects for non-food production. However, investors will need firm assurance of supply continuity as well as raw material costs in the new regime, before they can be expected to commit funds to bio-fuel plants.

Table 1. yield of five hemp varieties and percentage of the total yield of dry matter left as stubble in increments of 10 cm.
  Variety Total dry matter
leaf dry
stem dry matter
Percentage dry matter left as
    (t/ha)   (t/ha) 1st 10 cm 2nd 10 cm
  'F19' 21.6 31.4 14.8 8.1 7.3
  'F34' 19.6 24.2 14.9 8.6 8.8
  'F74' 20.5 19.6 16.5 7.9 7.7
  'Fasamo' 21.2 17.7 17.4 8.3 8.3
  Mean 21.2 24.5 16.0 8.2 7.9
  Standard Error 1.5 5.32 1.8  -  -

Hemp varieties and agronomy
     The results of one trial of five varieties indicate the yield levels achieved over the last three years (Table 1). The crop established quickly and smothered any developing weeds. Despite the height of the crop (up to 3 meters), no lodging occurred. Apart from Botrytis cinerea, no other pests or diseases were recorded. Crops flowered around mid-August and were cut with a disc mower in early September. Despite the large volume of green matter, the stems dried to 85% dry matter over a period of 7 to 10 days. The dried stems were wind rowed and baled without difficulty. While total biomass dry matter yield has been very high at 21.2 t/ha, the percentage of non-stem material was very high at 24.7%. Also, each increase of 10 cm in stubble height reduced the stem yield by approximately 8% (Table 1).
        Since the traditional focus of hemp agronomy has been to produce maximum yields of high-quality fiber, the effect of seeding rate on yield and stem dimensions was examined (Table 2). Reducing seed rate from the traditional 50 kg/ha to 20 kg/ha led to a significant increase in stem yield, due in part to a significant reduction in the number of extremely thin dwarf plants, a decrease in Botrytis-infected stems and an increase in stem diameter (Table 2).

Table 2. The effect of seedling rate on dry matter yield and stem diameter.
Seeding rate
Stem dry
matter yield
  (kg/ha) (t/ha) (mm)

Hemp as a biofuel
        If economic conditions favorable to a fuel use of arable crops arise from Agenda 2000, then hemp would be high on the list of preferred crops in Ireland for the following reasons:

        The main disadvantages are: