Cultivar, sowing date and plant density studies of fibre hemp (Cannabis sativa L.) in Tasmania

Abstract

This paper reports on a 3-year agronomic study into fibre hemp (Cannabis sativa L.) conducted in Tasmania, Australia. The performance of selected hemp cultivars, and the responses to sowing date and plant density were investigated as part of a broad feasibility study to assess the potential of fibre hemp and flax (Linum usitatissimum L.) as sources of fibre for the Australian newsprint industry.

Trials were conducted at separate sites in north-west and south-east Tasmania. Nine cultivars from the Ukraine, Hungary and France were examined in 2 separate trials. The Hungarian cultivars, Kompolti and Unico B, and the French cultivar Futura 77 had the highest single plot dry stem yields (up to 1500 g/m ² ) and bark proportions (up to 40%). All the cultivars flowered toward the end of January, suggesting that the growing season in Tasmania could accommodate much later flowering and potentially higher yielding genotypes. Levels of the psychoactive agent, delta-9-tetrahydrocannabinol were consistently below the legal maximum of 0.35% (dry weight basis).

Three sowing date trials were conducted across 2 seasons incorporating dates between mid September and mid November and a single autumn planting at the end of May. Interactions with cultivar and planting density were also considered. Stem and bark yield declined with delays in sowing after early–mid October in response to a decline in calendar days and thermal time from sowing to flowering. The response was most pronounced in sowings of Kompolti, which flowered within a short period and differed more substantially in durations to flowering. Earlier sowings were limited by premature flowering in response to shorter daylengths and by poor drainage at one of the 2 trial sites. The success of early sowings in Tasmania would appear to depend on finding cultivars less sensitive tophotoperiod, and cultivation on well drained sites.

A further trial was conducted to investigate the influence of plant density on hemp yields. Treatments included densities from 50 to 300 plants/m ² . Plant density declined with crop growth across all treatments and was most pronounced for populations of 200 and 300 plants/m ² . Final harvest stem yield responded in a parabolic manner to plant density, with maximum yields at about 110 plants/m ² . Differences in the percentage of the long, high quality bark fibre at final harvest were generally small and not significant. However, regression analysis of the response of bark percentage suggested a linear decline with increasing initial density.