Effect of nitrogen application rate and harvesting stage on yield and agronomic parameters of industrial hemp (Cannabis sativa L.)

Hemp (Cannabis sativa L.) is one of the world's oldest and most diversely cultivated plants, but legal constraints and a lack of agronomic rules have curtailed its production. This study aimed to determine the optimum nitrogen (N) application rate and harvesting stage for hemp yield in terms of seed, fiber, and stem. Treatments included (1) five nitrogen application rates (control [N0], 60 kg ha(-1) [N60], 120 kg ha(-1) [N120], 180 kg ha(-1) [N180], and 240 kg ha(-1) [N240]) and (2) three harvesting stages: before flowering (HS1), during flowering (HS2), and at the end of flowering (HS3). A 2-year field experiment was conducted with three replicates. Harvest stages were randomly distributed over N rates in both years. The following agronomic parameters were evaluated: plant height, stem diameter (lower, middle, upper), number of leaves/plant, leaflet width, leaflet length, dry stem yield, fiber yield, and seed yield. The highest stem yield and fiber yield were obtained in the 240 kg ha(-1) N treatment, and also the highest fiber (bast) yield and dry stem (hurd fiber) were obtained flowering and at the end of the flowering stages, respectively. When nitrogen application rate was increased from 0 to 240 kg ha(-1), plant height, stem, and fiber yields increased by 48%, 65% and 57%, respectively. Agronomic parameters increased significantly (p < 0.01) when the harvesting time was moved from "before flowering" to "at the end of flowering."