Agronomy of fibre hemp (Cannabis sativa L.) in Europe

Fibre hemp may yield up to 25 t above ground dry matter per hectare (20 t stem dry matter ha(-1)) which may contain as much as 12 t ha(-1) cellulose, depending on environmental conditions and agronomy. Its performance is affected by the onset of flowering and seed development. Effects of cultivar and management on yield and quality were tested at three contrasting sites in Italy, the Netherlands and the UK in three years, making use of standardised protocols for experimental design and research methodology. Highest yields (up to 22.5 t dry matter ha(-1)) were obtained in Italy when later cultivars were used. Attainable yields proved slightly lower in the Netherlands and much lower in the UK. The quality of the cellulose was relatively stable over the growing season, but lignification may proceed rapidly some time after flowering. Crop development was very rapid and crops maintained green leaf area for a long time, thus radiation interception was considerable. The radiation use efficiency changed during development. It was lower after flowering (about 1.0 g MJ(-1) PAR) than before (about 2.2 g MJ(-1) PAR). Growing earlier cultivars to obtain some seed set advanced the reduction in radiation use efficiency. Nitrogen proved to affect yield only slightly. A relatively small amount of fertiliser will be adequate to cover the crop's needs. Plant density declined during growth in a site-specific manner when it was high initially. Very low plant densities may not show this self-thinning but reduced yield and (especially) quality. Final plant densities were proven to depend more on initial plant stands than expected from literature. This was true at all three contrasting sites and in the different years. Nitrogen and plant density hardly interacted within one site. Results suggest that hemp can yield large quantities of useful cellulose when ecologically adapted cultivars are sown in proper plant densities. The cultivation is environmentally friendly with little harmful accumulation or emission of chemical inputs. More research on ideotyping is required and breeding efforts should be broadened. (C) 2000 Elsevier Science B.V. All rights reserved.