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EFFECT OF PLANT DENSITY, SOWING DATE AND IRRIGATION ON THE YIELD OF FIBRE HEMP (CANNABIS SATIVA) AND FLAX (LINUM USITATISSIMUM).

S.N. Lisson and N.J. Mendham

Department of Agricultural Science, University of Tasmania, Hobart, Tasmania 7001, Australia.

Abstract

Field trials with hemp and flax were conducted in Tasmania at two sites and over three seasons to screen imported cultivars and to investigate plant density, sowing date and irrigation responses. Both crops performed well under Tasmanian growing conditions with hemp yielding up to 1500 g/m2 of stem and flax up to 1000 g/m2 of stem and 200 g/m2 of seed. Hemp performed best when sown in early spring. However it would require substantial irrigation to achieve optimum yields as a summer crop in Tasmania. The optimum plant density for hemp was approximately 110 plants/m2 with ?self thinning? leading to yield declines at higher densities. Optimum stem and seed yields for flax were obtained from autumn sowings with supplementary irrigation late in the season. Rainfed, autumn sown flax production would also be possible. Flax was prone to lodge at plant densities in excess of about 1000 plants/m2.

Keywords Hemp, flax, density, cultivar, irrigation, sowing date.

The production studies reported in this paper formed part of a broader feasibility study assessing the potential for using the stem bark fibre of hemp and flax as a reinforcing agent in the Australian newsprint industry.

Hemp cultivar trials were conducted at Forthside (4110 S, 14640 E) in Tasmania?s north west and at Cambridge (4250 S, 14630 E) in the south east of the state to screen nine European cultivars. These included USO 11, USO 14, USO 13, Futura 77, Felina 34, Fedrina 74, Ferimon 12, Kompolti and Unico B. Further studies were undertaken to investigate the growth and development responses of the cv. Kompolti to various plant density, sowing date and irrigation treatments. Separate trials at Cambridge and Forthside investigated the effect of sowing dates from May through to November. A plant density trial at Forthside was comprised of plant density treatments from 50 to 300 plants/m2. An irrigation trial at Forthside included a range of allowable soil water deficits ranging from 30 mm to 120 mm below field capacity. A rainfed treatment was also included in the irrigation trial.

A flax cultivar trial was conducted at Cambridge to screen a range of European and Australian cultivars for their dual purpose fibre/seed cropping potential. The trial incorporated four European cultivars (Belinka, Ariane, Viking and Marina) and three Australian cultivars (Standard, Banner and Flag). Separate trials at Forthside and Cambridge investigated a range of sowing dates from May to October. Seeding rate trials covered a range of treatments from 30 to 140 kg/ha. Interactions between sowing date and seeding rate under both rainfed and irrigated (based on a 30 mm deficit) conditions were investigated in a further trial at Cambridge.

Results and discussion

Hemp studies

Of the nine hemp cultivars that were assessed, Kompolti and Futura 77 were the best performing, with oven dry stem yields of up to 1500 g/m2 and stem bark percentages of ~40%. With all cultivars flowering toward the end of January, it is clear that the growing season in Tasmania could accommodate much later flowering and hence potentially higher yielding genotypes.

The sowing date trials identified optimum yields from sowings in September. Later sowings resulted in a significant reduction in stem yield associated with a shortening of the thermal time duration from sowing to flowering. The main limitation with early sowings is the sensitivity of flowering to daylength. In a separate controlled environment study into the flowering response of Kompolti to photoperiod, flowering was found to occur rapidly in daylengths less than 14 hours and with increasing delay under longer days. With daylength not reaching 14 hours in Tasmania until early November, autumn and winter sown plants accumulate the thermal time requirement (basic vegetative period + photoperiod induced phase (1)) for flowering during a period when temperatures and particularly incident radiation are low.

The irrigation trial identified substantial water requirements for hemp cultivation. Under water deficit treatments of 30 mm and 60 mm which yielded the highest amount of bark fibre, total water consumption to a depth of 90 mm was 468 mm and 535 mm, respectively. The stem yields under rainfed conditions were significantly below those of irrigated treatments.

Stem yield responded in a parabolic manner to plant density, with maximum stem yields at about 110 plants/m2. This optimum plant density represented a balance between maximising the use of available resources and restricting plant losses associated with excessive competition at higher densities (?self thinning?).

Flax studies

The results from the flax cultivar trial indicated higher stem yields for the European cultivars than for the older Australian cultivars. Ariane was one of the better performing cultivars and under optimum conditions produced oven dry stem yields of up to 1000 g/m2 (~35% bark) and seed yields of 200 g/m2 (12-15% moisture).

Sowing date and irrigation studies with flax identified maximum stem and seed yields from an autumn sowing with supplementary irrigation from flowering to late rain fill. Good yields were also obtained from rainfed, autumn sowings. The success of later sowings would depend on irrigation during late spring and summer up to physiological maturity. This greater flexibility than hemp with regards sowing time and the potential for rainfed production, indicates possible benefits in terms of spreading production over time and also geographically around the state.

The selection of an optimum seeding rate for flax will depend to some degree on the sowing date and will involve a compromise between maximising yield and minimising potential losses from lodging. Autumn sowings gave maximum yields at approximately 1200 plants/m2, but were prone to lodge at densities in excess of approximately 1000 plants/m2. Lodging was more pronounced under irrigation. Later sowings in winter and spring were less prone to lodge and showed stem yield gains up to approximately 1100 plants/m2.

Conclusion

Both crops performed well under Tasmanian growing conditions. Hemp would perform best as an irrigated, spring sown summer crop. Flax might be grown either as an irrigated, spring sown crop or as a rainfed autumn sown crop. The optimum plant density is defined by a tendency for ?self thinning? in hemp and a susceptibility to lodging in the case of flax.

Acknowledgements

The authors would like to acknowledge the contribution of Lou Hanslow, Lyndon Butler and Vaughan Trebilco in the preparation and management of the field trials.

References

1. Major D.J. 1980. Canadian Journal of Plant Science, 60 (3), 777-784.

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