Efficient fertilization in the cultivation of Angelica acutiloba (Siebold & Zucc.) Kitag. in Hokkaido: Effect of amount of supplied nitrogen on growth, yield, and quality of A. acutiloba.

Angelica acutiloba (Siebold & Zucc.) Kitag., the source plant of the crude drug Angelicae acutilobae radix, is traditionally cultivated in western regions of Japan. Since A. acutiloba is now also grown in Hokkaido, the northernmost prefecture of the country, the cultivation method, especially the quantity of fertilizer, needs to be adapted because of the cooler climate and shorter growing period. In this study, we compared plant growth and harvest yield of A. acutiloba cultivated with different amounts of nitrogen (N) fertilizer. When plants were fertilized with 24 kg N/10 a, the aerial part was lush, and the diameter at the top of the root was about 1.3 times thicker than that in plants treated with 12 kg N/10 a. On the other hand, the weight of the harvested root grown with 24 kg N/10 a was slightly, although not significantly, less than that in plants grown with 12 kg N/10 a. In addition, we found that the content of (Z)-ligustilide, a major essential oil contained in A. acutiloba root, is affected by nitrogen application. Interestingly, it increased with increasing amounts of supplied nitrogen. However, the importance of Angelicae acutilobae radix as the crude drug is not limited to its (Z)-ligustilide content, and there are also other crucial quality features, such as having thick lateral roots, which were generated in this study with a moderate nitrogen application. We conclude that about 12 kg N/10 a is the optimal amount of nitrogen for healthy growth of A. acutiloba in Hokkaido.