Effects of water-fertilizer coupling on carbon and nitrogen stocks, physicochemical properties in soil and yield and saponin content of Panax notoginseng（Burkill） F. H.Chen ex C. H. Chow

【Objective】To investigate the effects of different water-fertilizer coupling conditions on the carbon and nitrogen stocks, physicochemical properties, and yield and saponin content of Panax notoginseng(Burkill) F. H. Chen ex C. H. Chow in P. notoginseng soil, and to provide theoretical basis for the study of P. notoginseng water-fertilizer regulation and soil carbon and nitrogen fixation potential. 【Method】The experiment was conducted at the P. notoginseng planting base in Luxi County, Yunnan Province, from 2019 to 2021. Three-year-old P. notoginseng was selected as the research object, and three irrigation levels W1(5 mm), W2(10 mm) and W3(15 mm) and four fertilizer application rates at different growth periods(rooting period, seedling period, flowering period and fruiting period) were set up F1(360-360-360-360 kg/ha), F2(288-360-432-360 kg/ha), F3(216-432-432-360 kg/ha) and F4(144-576-288-432 kg/ha), with no irrigated fertilizer as control(CK). The carbon and nitrogen stocks and physicochemical properties of P. notoginseng soils from different treatments at each growth period were determined, and fresh P. notoginseng plants were collected in November 2021 to determine their yields and saponin contents, and the relationships between soil carbon and nitrogen stocks and factors were explored using principal component dimensionality reduction analysis. 【Result】Soil carbon and nitrogen stocks under the same water-fertilizer coupling conditions decreased with the increase of soil depth, and basically showed the change rule of increasing and then decreasing with the advancement of growth period. Soil carbon and nitrogen stocks were the highest in the flowering period, with the maximum values of 82.07 t/ha(W1F4 treatment) and 4.41 t/ha(W2F3 treatment), respectively, and the key period for soil organic carbon stocks accumulation was in seedlingflowering period, and the key period for all-nitrogen storage accumulation was in the rooting-seedling periods. The nutrient content of each soil was higher in the W2F3 and W3F4 treatments, and decreasing the proportion of fertiliser applied at the rooting period and increasing the proportion of fertiliser applied at the seedling period improved the soil nutrient content. Soil carbon and nitrogen stocks were mainly dependent on the contents of total phosphorus, total potassium, available potassium, available phosphorus, nitrate nitrogen and ammonium nitrogen, and the increase of carbon and nitrogen reserves could improve the yield of P. notoginseng and the content of saponin R₁. The results of principal component dimensionality reduction analysis showed that the contents of total phosphorus, total potassium, ammonium nitrogen and nitrate nitrogen had a significant positive effect on carbon and nitrogen stocks(P<0.05). 【Conclusion】The changes of soil carbon and nitrogen stocks and nutrient content are convergent, in which W2F3 and W3F4 treatments are more favourable to soil carbon and nitrogen accumulation and nutrient increase, and the proportion of seedling fertilization should be increased appropriately to help increase soil carbon and nitrogen stocks and improve the yield of P. notoginseng.