Effect of Sowing Density and Date of Harvest on Yields of Industrial Hemp

Abstract

Hemp grown for textile applications must be sown at high densities (60–80 kg/ha) and harvested early to obtain fiber of high quality, and the interest in cultivating industrial hemp used for non-textile applications is growing. Broadening the use of hemp as a raw material for specific industrial products and obtaining maximum yields calls for revision of current sowing densities and harvest dates. Therefore, two experiments (A + B) have been carried out in 2004–2006 at the INF Experimental Farm in Pętkowo, Poland, near Środa Wielkopolska. In experiment A, four sowing densities of hemp grown for biomass, straw, panicles, and seed were tested (30, 40, 50, 60 kg/ha). In experiment B, lower sowing densities were compared for hemp grown for seed, panicles, and straw (5, 10, 15, 20 kg/ha). In both experiments, plants were harvested at three periods: beginning of panicle forming, full bloom, and full seed maturity. Panicles were harvested for essential oils. Results of field and laboratory testing confirmed a hypothesis that maximum yields of biomass, straw, cellulose, and fiber can be obtained at lower sowing densities (30 kg/ha) harvested at full bloom. When growing hemp for seed or panicles, the highest yields were obtained when hemp was sown at 10–20 kg/ha and harvested at full maturity of panicles. Following the results of the study, the norms for sowing hemp for non-textile applications used in agricultural practices require verification to increase yields of raw materials from 1 ha and to improve competitiveness of industrial products.