Effects of harvesting on the herbage yield, underground biomass and medicinal active ingredients of cultivated licorice

Abstract Licorice is an important Chinese medicinal herb, and its above‐ground parts are also useful as a legume forage. However, limited information is available on how the harvesting frequency impacts plant productivity, forage nutritional value, root growth parameters and medicinal compounds. This study aimed to determine the optimal harvesting frequency to maximize both the forage productivity and medicinal compounds in licorice by harvesting once (HF1), twice (HF2) or three times (HF3) per year in China Xinjiang Kuerle over 2 years. The results revealed that the dry matter yield and crude protein (CP) yield were greater in the HF3 treatment than in the other treatments. In HF3, the CP and crude fat contents were also relatively high, whereas the neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) contents were relatively low. In three‐year‐old licorice, increasing the harvesting frequency decreased the growth of the underground root system and the production of medicinal compounds. Compared with those in the HF1 treatment, the dry weights of single roots decreased by 16.65% and 47.08% in HF2 and HF3, respectively. In HF3, the glycyrrhizic acid content in the licorice roots was 0.48 ± 0.01%, which was significantly lower in HF1 (20%), whereas it was 0.6 ± 0.01% of that in HF1, leading to a decreased liquiritin content of approximately 49.28%. These results indicate that increasing the harvesting frequency during the growing period can not only increase the forage yield but also improve the forage quality. The CP content of forage increases with increasing harvest frequency, whereas antinutritional factors such as lignin and total tannins decrease; additionally, these effects impact the root mass and contents of medicinal compounds of licorice.