Harvesting

Hemp is a fast-growing crop that can be ready for harvest within 80-100 days after sowing. This timing is optimal for obtaining high-quality fine fibres suitable for both technical and textile applications. By the time of flowering, bast fibres have achieved the ideal balance of strength and fineness, particularly suitable for textile purposes (van den Oever et al., 2023). Hemp seeds are highly delicate. Despite the protective shell, minimal force is needed to crack the seed, leading to the oxidation of lipid reserves and consequent deterioration in product quality as triglycerides undergo alteration (Desanlis et al., 2013).

Hemp is a fast-growing crop that can be ready for harvest within 80-100 days after sowing. This timing is optimal for obtaining high-quality fine fibres suitable for both technical and textile applications. By the time of flowering, bast fibres have achieved the ideal balance of strength and fineness, particularly suitable for textile purposes (van den Oever et al., 2023). Hemp seeds are highly delicate. Despite the protective shell, minimal force is needed to crack the seed, leading to the oxidation of lipid reserves and consequent deterioration in product quality as triglycerides undergo alteration (Desanlis et al., 2013).

There is a distinction between harvesting for technical and for textile applications. For both applications, the harvesting is done with specific machinery. When harvesting with a focus on stem or fibre use, a distinction can initially be made between two main harvesting techniques. In the traditional use of hemp fibres for textiles, the aim is to obtain long fibres (TFZ, 2020). The quality of the long fibre harvest is determined by the parallel position of the plant or fibres during the entire harvesting and processing procedure. Ideally, the plant length should reach around 220 cm or slightly more. Specifically designed harvesters are used to mechanically cut the stalks into approximately 1-meter-long pieces, which are then arranged parallel on windrows in the field. This method enables the stalks to be processed on a flax scutching line following the retting process (van den Oever et al., 2023).

When using fibres for technical sector, for example for composite materials in the automotive industry or insulating materials, the focus of the harvesting technology is not on maintaining the parallel position of the plant material and the extraction of long fibres. This harvesting technique is characterized by the shortening of the stem. During this process, the stalks are cut into 60 cm pieces to prevent them from wrapping around the rotating parts of the machinery, both during harvesting and subsequent processing. After harvest, the hemp stems, referred to as "hemp straw," are arranged into windrows for the retting process. A windrow is a row of harvested crop arranged for further processing purposes (van den Oever et al., 2023). The harvesters are capable of separately collecting flowers and leaves.

The emergence of new uses, such as the extraction of cannabidiol (CBD) from the flowers and leaves of the hemp plant, means that new agricultural technology solutions are also being sought in this area.