Tasmanian hemp research

S.N. Lisson and N.J. Mendham

Department of Agricultural Science, University of Tasmania,
GPO Box 252C, Hobart, Tasmania, 7001, Australia.

          Lisson, S.N. and N. J. Mendham 1995.  Tasmanian hemp research.  Journal of the International Hemp Association 2(2): 82-85.
          A cultivar trial conducted during the 1994/95 season at Cambridge (147°30'E 42°50'S) incorporating Unico B, Fedrina 74, USO 11 and Kompolti showed that the later flowering Unico B and Kompolti cultivars gave significantly higher dry stem yields of 1357g/m² and 1174g/m² respectively.  It is apparent from the flowering times that the relatively long, dry summer season in Tasmania could accommodate later flowering and potentially higher yielding genotypes.
          Separate sowing date trials involving Kompolti and Fedrina 74 established at Cambridge and Devonport (146°40'E 41°10'S) demonstrated significant stem yield loss associated with delays in sowing date from mid September to early November, particularly with late flowering Kompolti. Stem yields from autumn sown Kompolti were restricted by waterlogging during the winter months and early flowering in September.  The success of early sowings in Tasmania clearly depends on finding later flowering genotypes and cultivation on well drained sites.
          Preliminary harvesting trials highlighted problems associated with dual purpose cultivation of hemp.  A 'dry' harvest system in which the straw is either baled or cut using a modified forage harvester seems appropriate for Tasmanian conditions and the intended end use of the fiber as a reinforcing agent in newsprint manufacture.

Introduction
          A cooperative research effort involving the Department of Agricultural Science, University of Tasmania and Australian Newsprint Mills Ltd. (ANM) commenced in early 1994.  The primary objective of this study is a broad feasibility assessment of using locally produced hemp (Cannabis sativa) and flax (Linum usitatissimum) fibre as a reinforcing agent in newsprint manufacture.  This involves an integrated analysis of the whole potential industry, with consideration of key crop management issues, industrial utilisation of crop products, and economic potential from both the farmers and manufacturers perspective.  The second aim of the research programme is to develop a crop growth model for hemp cultivation.
          This paper outlines results from preliminary trials conducted during the 1994/95 season and gives an overview of future and ongoing research.

Table 1.  Stem and component yield, seed yield, dates of flowering and seed harvest, %THC and plant density for hemp cultivar trial.

Method and design
Hemp cultivar trial
          The purpose of this trial was to rank the performance of a number of selected imported cultivars.  Any shortcomings in these genotypes and the potential for future improvement through local breeding was to be identified.
          Cultivars were selected on the basis of THC level, bark percentage and potential for late flowering.  With these criteria in mind, a range of cultivars have been selected for importation and assessment.  These included three from the Ukraine (USO-11, USO-14 and USO-13), four from France (Futura 77, Felina 34, Fedrina 74 and Ferimon 12) and two from Hungary (Kompolti and Unico B).  Four of these cultivars were assessed during the 1994/95 season.  The remaining cultivars will be screened in a second trial planned for the 1995/96 season.
          The trial was sown on the University of Tasmania farm at Cambridge on the 13th of October.

Sowing date trial
          Separate sowing date trials were established in the north of the state near Devonport and in the southeast at Cambridge.  Two cultivars were trialled, namely Kompolti and Fedrina 74.  Four separate sowing dates were selected over spring and at Cambridge, an additional late autumn sowing (May 30) of Kompolti was included for the purpose of comparison and assessment of the potential of hemp as a winter crop.

Harvesting trial
          A licence was also granted for a one hectare plot of hemp to conduct harvesting trials.  This larger area enabled preliminary evaluation of potential harvesting methods suited to the Tasmanian environment and the need for new machinery or modifications to existing equipment.
          It is believed that the relatively long, dry nature of our growing season and existing equipment is best suited to a 'dry' harvest system where the straw is dried naturally in the field prior to collection.  The crop was allowed to proceed through to seed maturity to assess dual purpose potential.  A range of equipment was trialled including a combine harvester, finger mower, draper style windrower, ground driven rake, round baler and chaff cutter.
          All trials were established with a sowing rate of 80kg/ha and a row spacing of 15 cm.  Fertilizer rates were based on literature recommendations modified according to soil nutrient status.  Crops were irrigated when soil moisture deficit exceeded about 35mm using overhead sprinklers.
          The date of flowering was taken as the time when 50% of the plants had one or more pedicillate male flowers or female flowers with styles clearly evident (Van der Werf et al 1994).  Seed maturity was taken as the time when 50% of the plants had seed that was dark brown in color and resistant to applied pressure.
          Determination of bark percentage of whole stem was based on a method used by De Meijer et al (1994).  Starting from about 15 cm above ground level, stem sections approximately 30 cm long were taken from 15 individual plants per plot.  Care was taken to select plants with a uniform diameter of approximately 7-10 mm measured at a height of 30 cm.  In the case of dioecious cultivars, only the females were selected.  The sections were then dried at 70 degrees Celsius for at least 24 hours prior to manual separation.
          Small losses from infection with Sclerotinia sclerotiorum and Alternaria sp. were observed during the growing season.  Losses were minimal and control was felt unnecessary.  The rapid growth rate and high plant densities afforded strong competiton with weed species thus negating the need for chemical weed control.  Substantial losses from bird damage were apparent just after emergence.  Bird control tape and hawk effigies were employed to minimise further losses.
          THC content was measured at State Government analytical laboratories using gas chromatography.  Readings were based on a composite subsample of the upper 25 cm of the main stem inflorescence of six individual plants.  In the case of dioecious cultivars, female plants only were sampled.
          Randomised complete block and split plot designs were used for cultivar and sowing date trials respectively.  Analysis of variance tests were performed using Systat 5.2 software.  Means were compared using the Fisher LSD test with significance for p values less than 0.05.

Table 2.  Stem and component yields, plant density, seed yield, flowering and seed maturity dates and bark percentage for sowing date trial, Devonport.

Results & Discussion
Cultivar trial
          The influence of flowering time on stem yield is clearly evident in Table 1 with the later flowering Hungarian cultivars, Unico B and Kompolti having significantly greater stem yields than Fedrina and USO 11.  The larger stem yield of Unico B was achieved with significantly fewer plants per unit area.  The low plant density was attributed to a poorer germination rate.  The plants have apparently compensated for this lower plant density by developing taller, thicker and branched stems.
          It is apparent from the flowering times that the relatively long, dry summer season in Tasmania could accommodate later flowering and potentially higher yielding genotypes.  Genotypic variability in flowering time and yield components exists within this species (De Meijer, 1994) and offers the potential for future breeding work to generate varieties more suited to cultivation in Australia.
          The seed yield of Unico B was significantly greater than all other cultivars and was attributable at least in part to a lower plant density.  Conversely, Kompolti had the lowest seed yield.
          Kompolti had a significantly greater percentage of bark in the stem than both USO11 and Fedrina.
          Content of both THC and CBD in collected samples is substantially less than that noted by other researchers (de Meijer S. pers. comm.).  Possible reasons for this include sampling at flowering rather than initial seed maturity (De Meijer et al 1992), the small sample size and differences in chemical analysis methods.

Sowing date trial
          Results from the sowing date trial (Table 2) at Devonport indicate significant stem yield loss associated with delays in sowing date from mid September to early November, particularly with late flowering Kompolti.  A similar trend was apparent for spring sowings at Cambridge.
          The May 30 sowing of Kompolti at Cambridge suffered losses from waterlogging during the winter months and flowered in the latter half of September at a height of 0.5m with oven dry stem yields of approximately 230 g/m².  A further sowing of Kompolti at the same site on August 30 showed an apparent dual flowering response with evidence of partial flowering in early November and the majority of flowering ocurring in late January.  The success of early sowings in Tasmania clearly depends on finding later flowering genotypes and cultivation on well drained sites.
          Kompolti seed used in the sowing date trial was from a different source to that used in the cultivar trial and had a higher germination percentage (89%).  This is reflected in the significantly larger harvest plant counts relative to Fedrina in the sowing date trial.  Furthermore, establishment on the clay loam soils at Devonport was superior to that on the duplex sandy loams at Cambridge, as shown by the relative plant densities for Fedrina at each site.
          Differences in bark percentage with delayed sowing were not significant.  Similarly, differences in seed yield for Kompolti were not significant.  However, an increasing trend in seed yield with delayed sowing was apparent with Fedrina.

Harvesting trial
          The conventional combine harvester was able to take seed off, but only by raising the cutter bar to the maximum allowable height of approximately 180 cm.  At this cutting height, more than the seed bearing portion of the stem was removed resulting in fibre yield losses.  In order to optimise the efficiency of the seed harvesting operation, timing is vital and even with good timing the efficiency is expected to be low due to the nonuniform nature of seed maturity.  Other potential problems with a dual purpose hemp crop include contamination from leaf and residual seed in the papermaking process, losses of stem yield in the wheel tracks, prolonged security risk and some potential risk associated with inadequate drying of the stem late in the season.  A more appropriate system might involve separate seed and fibre crops, managed in such a way as to optimise the yield and quality of each crop product.
          Having removed the seed, the remaining stem was then mown near ground level with a finger mower.  The narrow draper style windrower was clearly unsatisfactory for handling tall hemp crops.  Existing wide draper or augur type windrowing equipment designed for other crops may prove satisfactory for hemp harvesting.
          No major problems were encountered with the round baling of the stem.  Minor pickup blockages can be overcome by careful selection of groundspeed and a reduction in windrow volume.
          In order to overcome problems with fibre tangling in the pulping of hemp, the stem or bark fibre will need to be cut into lengths of 5-10 mm.  With this in mind, it was felt that another possible harvesting option might be to pass the stem through a modified forage harvester and feed the cut straw into a hopper bin.  To assess this, retted and unretted stem material was passed through a stationary five-bladed chaff cutter.  A more uniform cutting length could be achieved by ensuring the stem is fed end on to the cutter, by minimising the gap between blade and cutting face, having sharp blades and employing a sieving table with feedback of over-long pieces.  The action of cutting seemed to separate the bark and core fractions quite effectively.  Further separation of the two components for pulping trials was afforded by floatation in water.

Ongoing and future research

Pulp and papermaking trials
          The Tasmanian operation of ANM produces approximately 40% of Australia's newsprint requirements from a blend of eucalypt chemo-mechanical pulp (CMP), radiata pine thermo-mechanical pulp (TMP) and a small amount (3%) of imported long-fibre kraft pulp.  The purpose of the kraft supplement is to provide additional strength to the newsprint. Interest from ANM in this current study lies in assessing the potential of replacing the kraft component with locally grown hemp and flax, pulped with existing mechanical processes.  Potentially, ANM would benefit from being able to source and process the required long fibre supplement locally, thus freeing them from fluctuations in the world price and availability of kraft pulp.  The key processing questions are whether or not it is possible to produce a mechanical pulp with properties at least equivalent to kraft and for a price somewhat less than the imported option.  Laboratory pulping trials and an economic assessment will be directed toward answering these questions.  Emphasis will be given to evaluating and optimising the existing chemo-mechical (CMP) and thermo-mechanical (TMP) processes with hemp and flax as raw materials.  Pulp evaluations will be made of the whole stem as well as the core and bast fractions of hemp and flax.

Economic feasibility assessment
          Work has recently commenced on an economic feasibility assessment of a hemp and flax based industry.  This will investigate development potential and strategies and issues to develop the industry.  Preliminary budgets have emphasised the need for utilising the whole stem in order for a future industry to be economically viable.  Application of the core fraction in the newsprint as well as non-paper end uses is currently being investigated.

Crop growth model
          The legal status of hemp requires that trial and commercial cropping activities be conducted under strict licencing arrangements.  This coupled with the high cost of traditional agronomic trials suggests a potential role for a crop growth model.  Such a model would aid decision makers in the assessment of production potential at a given site.  It is intended that the model will be based on a similar model developed for kenaf (Carberry et al 1992) and predict key phenological events and potential stem and bast fibre yield from crop management and local environment inputs.
          Forthcoming trials will investigate key aspects such as leaf area development, pre-emergent growth responses to temperature and flowering responses to daylength.

Irrigation trials
          It is apparent that irrigation is one of the major variable costs associated with hemp cultivation in Tasmania.  Irrigation is necessary to overcome deficiencies in both the distribution and total amount of rainfall over the summer months in Tasmania.  It was next decided to conduct an irrigation trial with hemp in order to gain an understanding of its effect on yield and growth responses, according to different irrigation schedules based on a range of refill points.

References

• Carberry, P., Muchow, R, Williams, R., Sturtz J and McCown R., 1992.  A simulation model of kenaf for assisting fibre industry planning in northern Australia.  1.  General introduction and phenological model.  Aust. J. Agric. Res. 43: 1501-13.
• Meijer, E. de 1994.  Diversity in Cannabis. Doctoral thesis.  Wageningen University.
• Meijer, E. de, Van der Kamp, H. and Van Eeuwijk, F. 1992.  Characterisation of Cannabis accessions with regard to cannabinoid content in relation to other plant characters.  Euphytica 62: 187-200.
• Meijer, E. de and Van der Werf, H. 1994.  Evaluation of current methods to estimate pulp yield of hemp.  Industrial Crops and Products 2: 111-120.
• Werf, H. van der, Haasken, H. Wijlhuizen, M. 1994.  The effect of daylength on yield and quality of fibre hemp (Cannabis sativa L) European Journal of Agronomy 3 (2): 117-123.