Optimum combination of chemical and bio-organic fertilizers for high active components and low heavy metals in the cultivation of Ophiopogon japonicus (Linn. f.) Ker-Gawl

Objectives The optimum combination of nitrogen (N), phosphorus (P), potassium (K) and bio-organic fertilizers (BF) was studied for the cultivation of Ophiopogon japonicus (Linn. f.) Ker-Gawl, so as to achieving products with high medical quality and safety.

Methods L₉ (3⁴) orthogonal design was used in a field experiment. The contents of quality related active components, specific O. japonicus saponins and heavy metals were determined. The DTOPSIS method was used for comprehensive optimization of the fertilizers.

Results Rational application of N, P, K and bio-organic fertilizer could significantly increased the contents of water-soluble extracts, total saponins, soluble polysaccharides, saponins D and saponins D', and decreased the contents of Cu, Ge, As, Pb and Hg. Among them, water-soluble extracts, the contents of total O. japonicus saponins, saponins D and saponins D' were the highest in the treatment of N₁P₃K₃BF₃, in which they were 74.52%, 0.38%, 112.208 μg/mL and 56.293 μg/mL respectively, and the highest content of soluble polysaccharides was in N₃P₃K₂BF₁ (42.47%). The lowest content of Cu and Pb were in N₁P₂K₂BF₂, the lowest As in N₃P₂K₁BF₃, the lowest Cd in N₂P₁K₂BF₃, and the lowest Hg in N₂P₂K₃BF₁.

Conclusions Through the evaluation of DTOPSIS method, the optimum combination of fertilizers is chemical N 598 kg/hm², P₂O₅ 240 kg/hm², K₂O 595.80 kg/hm² and bio-organic fertilizer 2700 kg/hm².