Effects of cow manure and humic acid on Echinacea purpurea (L.) performance and essential oils accumulation under drought conditions

Drought is a significant environmental stress factor and plays an important role in reducing crop productivity under drought stress conditions. In a field experiment we examined the effects of drought and fertilizer sources on coneflower performance. The fertilizer sources included CF (chemical fertilizer) with 80 kg N/ha and 32 kg P/ha, CM (20 t/ha cow manure), CMH(3:1) (15 t/ha CM + 1 kg/ha humic acid), CMH(1:1) (10 t/ha CM + 2 kg/ha humic acid), and CMH(1:3) (5 t/ha CM + 3 kg/ha humic acid). The results revealed significant interactive effects of water status and fertilizer source on various parameters including morphological, biochemical, biomass and productivity parameters and essential oil production. Proline content significantly increased in all fertilizer treatments under drought conditions (42–100 %). However, carotenoids and essential oil content increased in the CM and CF treatments by 41 % and 81 %, respectively, under drought conditions. Photosynthetic pigments, stem, and flower weights in the CMH(3:1) and CMH(1:1) treatments did not significantly differ between drought and non-drought conditions. The CMH(3:1) treatment resulted in the highest plant height, number of stems, leaves, and flowers, aboveground biomass, and essential oil yield under drought conditions. Furthermore, the aboveground biomass and essential oil yield of the CMH(3:1) treatment were 34 % and 9 % higher, respectively, than with chemical fertilizer under non-drought conditions. In conclusion, the application of 15 t/ha of cow manure along with 1 kg/ha of humic acid can serve as a suitable alternative to mineral fertilizers for achieving optimal coneflower production under varying water availability conditions. • First study on coneflower fertilized with humic acid-enriched cow manure (CHM). • Photosynthetic pigments in CHM were similar in drought and non-drought conditions. • Under drought, CMH(3:1) EO yield equalled mineral fertilizer yield in non-drought. • In drought, CMH(3:1) biomass was 34 % higher than mineral fertilizer in non-drought. • CMH treatments created more resilience of plants against drought effects.