Effect of water and fertilizer regulation on the soil microbial biomass carbon and nitrogen, enzyme activity, and saponin content of Panax notoginseng

Improper irrigation by Panax notoginseng growers can lead to soil consolidation, low fertilizer utilization, and decreased yield quality. In an attempt to provide a scientific and theoretical basis for Panax notoginseng cultivation to improve soil microhabitat and yield quality, field experiment were conducted on three-year-old Panax notoginseng in 2019, 2020, and 2021. The experimental design consisted of two control factors, the amount of irrigation (W) and the amount of fertilizer (F) applied. The irrigation was set to three levels, as W1, W2, and W3, with exact irrigation volumes of 5 mm, 10 mm, and 15 mm. The amount of fertilizer applied was different in all four growth stages. The amount of fertilizer applied according to the four growth stages (rooting stage: seedling stage: flowering stage: fruiting stage), where F1 (360–360–360–360 kg hm−2), F2 (288–360–432–360 kg hm−2), F3 (216–432–432–360 kg hm−2) and F4 (144–576–288–432 kg hm−2). The W and F were randomly combined to form a total of 12 treatments. And a control treatment (CK), was added, and CK was neither irrigated nor fertilization. For obtaining the best treatment results, the TOPSIS method was used to comprehensively evaluate the soil microbial biomass carbon and nitrogen, enzyme activity, physiological growth and saponin content of Panax notoginseng in 13 different water and fertilizer treatments. The results indicated that microbial biomass carbon and nitrogen, urease, sucrase, acid phosphatase and catalase activities of Panax notoginseng soil were significantly different (P < 0.05) and varied with the growth stage. The comprehensive evaluation by the TOPSIS method ranked W3F4 first and was the optimal treatment. The W3F4 treatment was more beneficial to the quality of Panax notoginseng than the other 12 treatments. W3F4 had the largest soil microbial biomass carbon and nitrogen content. W3F4 had the highest urease, sucrase, acid phosphatase, and catalase activities, which were 1.95, 1.69, 2.32, and 1.47 times higher than the CK treatment, respectively. W3F4 significantly improved R1, Rg1, Re, Rb1, and Rd saponin content. This study provided a theoretical basis for the water and fertilizer regulation of Panax notoginseng with its green, healthy and efficient quality cultivation.