Lowering Nitrogen and Increasing Potassium Application Level Can Improve the Yield and Quality of .

Excessive nitrogen (N) application and potassium (K) supplement deficiency is a common problem in cultivation. However, synergistic effects of lowering N and increasing K application on yield and quality of have not been reported. Field experiments in two locations with different N and K combined application were conducted to study the effects on yield and quality. Then, the saponin accumulation mechanisms were explored by pot and hydroponic culture with 2- or 3-year-old seedlings. The investigation showed that 70% of cultivation fields reached abundant levels of total nitrogen (TN) but had deficient levels of total potassium (TK), which may be detrimental to balance the N/K uptake of . Moreover, the average biomass was 18.9 g, and saponin (PNS) content was 6.95%; both were influenced by the N/K values of . The field experiments indicated that compared to the conventional N and K application (N:K = 2:1), lowering N and increasing K application (N:K = 1:2) decreased root rot rate by 36.4-46.1% and increased survival rate, root biomass, and yield, as well as PNS content by 17.9-18.3, 5.7-32.9, 27.8-57.1, and 5-10%, respectively. The mechanism of lowering N and increasing K application on the PNS content improving was due to the decreasing of N/K value, which promoted photosynthesis, sugar accumulation, and the expression of saponin biosynthesis genes. Therefore, lowering N and increasing K application to the ratio of 1:2 would have great potential to improve the synergistic effect on yield and quality of cultivation.