Objectives Unreasonable chemical fertilizer application impacts the yield and quality of Angelica dahurica var. formosana, a widely used Chinese medical herbs. We studied a green fertilization technology using the isolated rhizosphere fungi A. dahurica var. formosana with suitable chemical and organic fertilizers.

Methods A field experiment was conducted in Suining, Sichuan Province. The tested microbial agent was prepared from Aspergillus niger ZJ-17 isolated from A. dahurica var. formosana rhizosphere. There were eight treatments in the experiment: half-fertilizer (T1), full-fertilizer (T2), half fertilizer+A. niger ZJ-17 seed application (T3), half fertilizer+A. niger ZJ-17 watering root (T4), full fertilizer+A. niger ZJ-17 seed application (T5), full fertilizer+A. niger ZJ-17 watering root (T6), no fertilizer (T0) and full fertilizer+commercial A. niger seed application (effective viable bacteria number≥10 billion/g, T7). Full fertilizer rate was composed of 750 kg/hm² oil cake, 139.5 kg/hm² urea, 2193.8 kg/hm² superphosphate, 240 kg/hm² potassium sulfate, and half fertilizer rate applied half amount of all the used fertilizers. The applying amount of the used microbial agent ( 3.0×10⁸ CFU/mL) was 30 L/hm², equaling to 0.06 L in each plot. Seed application was performed by pouring the microbial solution on the seed surface, and root irrigation by watering the microbial solution near the root soil in March of the next year. After seeding, plant samples were taken in frequency of every two months for determination of agronomic traits and plant nutrient content. At harvest, the quality and yield of A. dahurica var. formosana were analyzed, and the colonization of A. niger in soil was measured by fluorescence quantitative method.

Results Seed application led to significantly higher colonization rate of A. niger than root application, commercial A. niger also colonized effectively in soil. Compared with T2, T5 treatment significantly increased plant height, root length and root diameter of A. dahurica var. formosana at harvest stage by 11.57%, 10.85% and 16.70% (P<0.05), the root yield and economic benefit by 16.33% and 19.94%, the accumulation of N, P and K in the underground part by 37.73%, 21.18% and 28.75%, increased the accumulation of total coumarins significantly. T5 also showed significantly higher promotion effect than T6 and T7 treatment. Under semi-fertilizer condition, T3 increased the contents of imperatorin and isoimperatorin of A. dahurica var. formosana at harvest stage by 9.82% and 22.45% (P<0.05), T5 did not show significant effect on them.

Conclusions Under conventional fertilizer application rate (full fertilizer), seed applying A. niger ZJ-17 can significantly improve the growth index, yield and benefit of A. dahurica var. formosana. Root application does not have the promotion effects. Under half fertilizer rate, seed applying A. niger ZJ-17 improved the imperatorin and isoimperatorin content, but decreased yield and benefit of A. dahurica var. formosanathan. Therefore, the suitable fertilizer rate needs further researching in practical production of A. dahurica var. formosana.