Suitable soil moisture contents for water use efficiency and saponins accumulation in Panax notoginseng

The moisture content in the soil directly affects the yield and quality of Panax notoginseng, especially at the age of three years old. However, the suitable moisture for the growth of P. notoginseng is unknown. In this study, the effects of different soil moisture on the growth of P. notoginseng were studied.

Four different water treatments (0.45 field capacity (FC), 0.60 FC, 0.70 FC, and 0.85 FC) were set up in Shilin County, Yunnan Province, China. The water consumption and daily dynamic of water consumption were determined daily (from April 21 to October 18, 2012), and the daily dynamic of water consumption under different weather conditions (sunny and rainy) was determined. The transpiration coefficient and water use efficiency were calculated through dry matter accumulation and total water consumption. Accumulation of saponins of roots of P. notoginseng were analyzed by HPLC after treated, and the soil moisture content suitable for the growth of P. notoginseng was estimated by regression fitting of the active ingredient accumulation and the soil moisture content.

The water consumption of 0.85 FC, 0.70 FC, 0.60 FC and 0.45 FC were 2.89, 3.68, 3.37 and 2.73 kg/plant per day, respectively. The water consumption of P. notoginseng from June to August was greater than other months. The daily dynamic of water consumption on sunny days and sunny days after rain showed a "double peak" feature, and it showed a "single peak" feature on rainy days. The water uses efficiency (WUE) of 0.85 FC, 0.70 FC, 0.60 FC and 0.45 FC were 2.51, 3.32, 4.59, 3.39 gDW/kg H₂O, respectively. The increase of soil moisture content would reduce the WUE of P. notoginseng. With the increase of soil water content, the content of notoginsenoside R₁ and ginsenoside Rg₁ did not change significantly, while the content of ginsenoside Rb₁ and Rd showed a decreasing trend.

Soil moisture content significantly affected the water consumption of P. notoginseng, and when it was 56.4% of the maximum water holding capacity in the field, the sum of the four saponins of 100 strains of P. notoginseng was the highest.