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 s tem dry matter ha(-1)) which may contain as much as 12 t ha(-1) cellulose, depending on environmental conditions and agronomy. Its performance is affe cted by the onset of flowering and seed development. Effects of cultivar an d management on yield and quality were tested at three contrasting sites in Italy, the Netherlands and the UK in three years, making use of standardis ed protocols for experimental design and research methodology. Highest yiel ds (up to 22.5 t dry matter ha(-1)) were obtained in Italy when later culti vars were used. Attainable yields proved slightly lower in the Netherlands and much lower in the UK. The quality of the cellulose was relatively stabl e 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. T he 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). Gr owing earlier cultivars to obtain some seed set advanced the reduction in r adiation use efficiency. Nitrogen proved to affect yield only slightly. A r elatively small amount of fertiliser will be adequate to cover the crop's n eeds. Plant density declined during growth in a site-specific manner when i t was high initially. Very low plant densities may not show this self-thinn ing 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 sugge st that hemp can yield large quantities of useful cellulose when ecological ly adapted cultivars are sown in proper plant densities. The cultivation is environmentally friendly with little harmful accumulation or emission of c hemical inputs. More research on ideotyping is required and breeding effort s should be broadened. (C) 2000 Elsevier Science B.V. All rights reserved.