Coupling effects of irrigation level and terrain slope on disease, yield and quality of Panax notoginseng under micro-sprinkler irrigation

At present, the state has introduced the policy of forest Chinese herbal medicine planting planning, strictly prohibiting the planting of Chinese herbal medicine in basic farmland, coupled with the fact that the continuous cropping obstacles of Panax notoginseng have not yet been solved, which makes the area of arable land suitable for planting become less and less. However, the effect of soil moisture regulation on the growth of Panax notoginseng cultivated on sloping arable land has not been reported. Thus, the aim of this study was to investigate the impact of various irrigation levels and slopes on Panax notoginseng agronomic traits, physiological characteristics, disease attributes, biomass, and quality characteristics. During 2018–2020, a field experiment was conducted in the Panax notoginseng growing seasons with three irrigation levels (I1: 70–75% θ_FC, I2: 75–80% θ_FC, I3: 80–85% θ_FC) and three slopes (S1: 2.43°, S2: 6.38°, S3: 16.38°). The results evidenced that the photosynthetic characteristics, root hydraulic conductivity characteristics, biomass and PNS of Panax notoginseng reached the maximum value in the I2S2 treatment, and at the same time, the incidence rate of Panax notoginseng root rot was the lowest. Therefore, based on the results of this study, irrigation volume I2S2 should be regarded as the optimal slope and irrigation management strategies for reducing Panax notoginseng diseases and realizing stable yield and quality improvement of Panax notoginseng. A multi-objective optimization model was established through binary quadratic regression analysis. The findings evidenced that when the irrigation interval was 187–203 mm and the slope interval was 5–10.7°, Panax notoginseng had the lowest incidengce rate, and the root biomass and saponin content reached > 95% of the maximum values at the same time.