Coupling Effect of Water and Soluble Organic Fertilizer on Yield and Quality of Panax notoginseng under Micro-Sprinkler Irrigation in Southwest China

Abstract

The cultivation of Panax notoginseng has been plagued by a multitude of challenges, including recurrent diseases, suboptimal value, inadequate quality, and environmental degradation resulting from improper water and fertilizer management. To address these issues and improve the yield of P. notoginseng and its saponin content, this study endeavors to identify the optimal irrigation and fertilization levels in shaded environments in Yunnan Province in Southwest China. In this field experiment, three-year-old plants were tested to evaluate the effects of water, soluble organic fertilizers, and their combinations on plant growth, physiological parameters, yield, and saponin content. The experiment included 12 treatments with three types of irrigation (10 (W₁), 15 (W₂), and 20 (W₃) mm), totaling 440, 660, and 880 mm, and four levels of the total amount of fertilization (F₁ (60, total N 12.6, total P 5.5, and total K 10.5 kg ha⁻¹), F₂ (90, total N 18.9, total P 8.3, and total K 15.7 kg ha⁻¹), F₃ (120, total N 25.2, total P 11.0, and total K 20.9 kg ha⁻¹), F₄ (150, total N 31.5, total P 13.8, and total K 26.1 kg ha⁻¹)). The randomized complete block design was used, with 36 plots in total and 3 replications. The study utilized the TOPSIS method to determine the most effective water and fertilizer management strategy for the growth and production of P. notoginseng. The assessment of yield, water and fertilizer productivity, and saponin content across all treatments revealed that the W₃F₃ treatment resulted in significant increases in the plant’s height, stem diameter, and net photosynthetic rate. Meanwhile, the W₂F₃ treatment exhibited the best root morphological traits. The W₃F₄ treatment effectively increased dry matter and transpiration. The combination of water and fertilization had a coupling effect that not only increased yield to 1400 kg ha⁻¹ but also improved water–fertilizer productivity. The application of the W₂F₃ treatment resulted in a significant increase in the accumulation of active components, leading to a total P. notoginseng saponin (PNS) content of 24.94%. Moreover, the comprehensive index obtained through the TOPSIS model indicated that the W₂F₃ treatment outperformed other treatments. Therefore, this treatment can be considered a promising water and fertilizer model for P. notoginseng cultivation, which can enhance its yield, quality, and productivity while promoting sustainable green development.

1. Introduction

Panax notoginseng is a perennial herb belonging to the Araliaceae family and is primarily found in Southwest China, growing at an altitude range of 1200 to 1800 m [1,2]. It possesses hemostatic, detumescence, and pain-relief properties, making it effective in treating cancer, cardiovascular disease, and atherosclerosis [3,4,5]. Yunnan produced over 90% of P. notoginseng in China, and the industry’s output value there increased from around CNY 380 million in 2000 to approximately CNY 38 billion in 2020. Thus, improving P. notoginseng quality benefits both human health and local economic development. However, excessive irrigation, chemical fertilizers, and pesticide usage cause soil acidification, increased incidence rates of P. notoginseng, and decreased yield and quality [6,7]. Therefore, a realistic irrigation and fertilization regulation management tactic was required to develop green products and protect the ecological environment of P. notoginseng while managing yield and quality pressures.

P. notoginseng was irrigated primarily based on historical experience and without any scientific direction, which resulted in a significant waste of water resources and made P. notoginseng susceptible to ponding and stunted root growth [8]. Excessive soil water reduced soil aeration, inhibited the physiological metabolism and extension of roots, reduced the absorption of nutrients by roots and the active elements in plants, and ultimately led to reduced yield and the frequent occurrence of root rot [6,9,10,11]. In addition, the pressure caused by the water shortage will hinder gas exchange, limit photosynthesis, affect the accumulation of dry matter, and reduce yield [8,12,13]. For increasing production and quality, efficient water management strategies are essential for P. notoginseng’s industrial growth. By keeping the balance between nutrition and reproductive growth, moderate irrigation not only enhances the physiological properties of plants but also increases production [14,15,16]. Yet, relatively little research has been undertaken on how moderate irrigation affects P. notoginseng production and quality.

For enhancing crop yields, fertilizer is the second most important factor [17]. In order to make up for the lack of nutrients in red soil and obtain a higher yield, P. notoginseng was treated with a large number of chemical fertilizers during the planting process [11,18,19]. This resulted in soil acidification, nutrient loss, and nitrate pollution, and the remaining chemical fertilizer would also be discharged into the soil and surrounding waters in large amounts, causing great damage to the ecology [11,20]. A reasonable fertilizer plan is needed to ensure the long-term growth of agriculture [21]. To improve soil health and increase crop yields, organic fertilizers are a great alternative to chemical fertilizers [22,23]. The benefits of applying organic fertilizer to soil include the strengthening of soil physical properties, the preservation of fertilizer and water functions, the enhancement of soil nutrient content, the improvement of soil microbial community structure and microenvironment, and the promotion of crop growth for roots and branches [24,25,26,27,28,29]. Consequently, more research was required to determine how organic fertilizer affected P. notoginseng during planting.

P. notoginseng has largely been grown in Yunnan Province using conventional field management techniques. Despite earlier research that concentrated on a single factor, such as fertilization or irrigation, this strategy did not address the difficulties of juggling various goals, such as high efficiency, yield, and quality. Some of these studies were conducted in a controlled pot experiment environment, which would limit their applicability in field studies [30]. A more thorough approach was needed to manage water and fertilizer efficiently, increase output performance, and reduce waste. Consequently, water and fertilizer management strategies based on P. notoginseng yield and quality were urgently investigated. As a result, we sought to investigate the effects of irrigation in conjunction with soluble organic fertilizer on the growth, photosynthesis, dry matter, yield, and quality of P. notoginseng in this study. In 2019, micro-sprinkler irrigation and shading were used in a field experiment. Thus, this study aimed to (1) investigate the effects of irrigation mixed with soluble organic fertilizer on P. notoginseng growth physiological characteristics, dry matter, yield, and quality and (2) use the TOPSIS approach to construct a complete evaluation model of total yield, water–fertilizer productivity, and saponin content to establish a more effective irrigation and soluble organic fertilizer management strategy.

2. Materials and Methods

2.1. Plant Material and Field Experiment Site

From March 2019 to January 2020, three-year-old plants were investigated at the Luxi Research and Demonstration P. notoginseng Base, which was located in Wujiepu Town of Luxi City, Yunnan Province, China, at 24°26′ N, 103°34′ E, and 1945 m height. The experimental site base belongs to the subtropical monsoon climate zone. The annual average sunshine is 2100 h, the average annual rainfall is 950 mm, the frost-free period is 273 days, the average relative humidity is 75%, and the main wind direction is southwest. The soil is red soil (pH = 6.60), with a soil bulk density of 1.31 g cm⁻³, field capacity of 0.55 cm³ cm⁻³, total nitrogen of 0.97 g kg⁻¹, total phosphorus of 0.86 g kg⁻¹, total potassium of 12.41 g kg⁻¹, nitrate nitrogen of 8.10 mg kg⁻¹, ammonium nitrogen of 19.01 mg kg⁻¹, available phosphorus of 11.31 mg kg⁻¹, and available potassium of 316.47 mg kg⁻¹. The proportions of clay, silt, and sand in the soil (0–40 cm) of the experimental site were 8.7%, 34.1%, and 57.2%, respectively, and the soil was classified as silty clay loam soil.

2.2. Experimental Design, Field Management, and Agronomic Practices

In this study, the experiment treatments included three levels of irrigation amount (W₁, W₂, and W₃) with 10, 15, and 20 mm, respectively, and four levels of soluble organic fertilization (F₁, F₂, F₃, and F₄) with 60, 90, 120, and 150 kg ha⁻¹ [31,32]. The precise watering and fertilization schedule is shown in

Table 1. Experiment design of various irrigation and soluble organic fertilization levels for P. notoginseng.

Treatments		Irrigation Amount (mm)		Fertilization Amount (kg ha−1)
Irrigation Level (W)	Soluble Organic Fertilization Level (F)	Total Irrigation Amount	Single Irrigation Amount	Single Fertilization Amount	Total Fertilization Amount	Total N	Total P	Total K
W1	F1	440	10	5.5	60	12.6	5.5	10.5
	F2	440	10	8.2	90	18.9	8.3	15.7
	F3	440	10	10.9	120	25.2	11.0	20.9
	F4	440	10	13.6	150	31.5	13.8	26.1
W2	F1	660	15	5.5	60	12.6	5.5	10.5
	F2	660	15	8.2	90	18.9	8.3	15.7
	F3	660	15	10.9	120	25.2	11.0	20.9
	F4	660	15	13.6	150	31.5	13.8	26.1
W3	F1	880	20	5.5	60	12.6	5.5	10.5
	F2	880	20	8.2	90	18.9	8.3	15.7
	F3	880	20	10.9	120	25.2	11.0	20.9
	F4	880	20	13.6	150	31.5	13.8	26.1

. The experiment was conducted with three replicates for each treatment, randomly distributed within 36 plots. Each plot had an area of 22.8 m² and was irrigated with an independent micro-sprinkler irrigation system. A lateral pipe with a control valve and a water meter was installed in each plot to control the amount of irrigation. The irrigation and fertilization processes utilized the MixRite2502 water fertilizer integrated equipment from Israel’s TEFEN Company. The fertilizer used was a water-soluble organic compound fertilizer (21% N–21% P₂O₅–21% K₂O + 6% humic acid + trace elements) produced by Sichuan Shifang Demei Industrial Co., Ltd. A rain shelter was set up with plastic film at a height of 2.5 m. The experimental site was treated with three layers of net, providing 8.3% light transmittance [6]. P. notoginseng seedlings were transplanted at a density of 4.4 × 10⁵ plants ha⁻¹ after being purchased from local farmers in Luxi County. The layout is illustrated in Figure 1. Pine needles that were 5 mm thick were then used to cover the surface of each plot. Other management procedures, such as plant trimming, controlling insects, and controlling weeds were carried out with the help of the local farmers’ experience.

2.3. Measurements

2.3.1. Growth and Physiology of P. notoginseng

(1)

Growth index: Three healthy and equally developing P. notoginseng plants were randomly selected at various stages of growth for this investigation. The plant height was measured using a ruler, and the stem diameter was measured at 1 cm from the ground with a vernier caliper. Root samples were gathered using the monolith method [33] and cleaned to eliminate dirt. The WinRHIZO root analysis system was used to scan and inspect the roots, as well as collect data on their morphology [34]. Each step was repeated three times.

(2)

Photosynthetic characteristics: The photosynthetic characteristics of P. notoginseng leaves were measured using the LI-6400 photosynthetic apparatus (LiCor, Lincoln, NE, USA) under clear, cloudless, and natural light conditions from 9 A.M. to 12:00 A.M. at the seedling, budding, flowering, and fruiting stages. We repeated each treatment three times, randomly selected disease-free, evenly growing, and fully stretched P. notoginseng leaves for each repetition, and fixed and labeled them [8].

(3)

Canopy water conductivity of P. notoginseng: P. notoginseng plants that were uniformly growing and disease-free were chosen and intercepted 1 cm from the ground. The HPFM high-pressure current meter’s quasi-steady flow rate technique was used to assess canopy hydraulic conductivity [35], and this was repeated three times to achieve reliable results.

(4)

Dry matter and yield: We randomly selected three plants from each plot for cleaning and cutting off their roots and tree crowns. The sample was placed in an oven at 105 °C for 30 min and dried to a constant weight at 50 °C. Finally, the dry matter of the sample was weighed. Yield was determined by measuring the dry matter of the harvested roots. The calculation methods for root–shoot ratio and root drying rate were as follows [11]:

$$Root shoot ratio=M_1/M_2$$

(1)

$$Root drying rate=M_1/M_0$$

(2)

where M₀ is the wet weight of the underground part, g; M₁ is the dry weight of the underground part, g; and M₂ is the dry weight of the overground part, g.

2.3.2. Irrigation Water Productivity (IWP) and Partial Fertilizer Productivity (PFP)

IWP and PFP were calculated as follows [6,36]:

$$IWP=Y/I$$

(3)

$$PFP=Y/F$$

(4)

where Y is the yield of P. notoginseng, kg ha⁻¹; I is the total irrigation amount, mm; IWP, kg m⁻³; F is the total mass of soluble organic fertilizer, kg ha⁻¹; PFP, kg kg⁻¹.

2.3.3. Saponin Content of P. notoginseng

To determine the content of five saponins (R₁, R_g1, R_e, R_b1, and R_d) in P. notoginseng, the LC-20AB high-performance liquid chromatograph produced by Shimadzu Company of Japan was utilized. The total P. notoginseng saponins (PNS) are the sum of the five saponin contents. The first step was to rinse the plants with clean water and dry them in the air before decolorizing them in an envelope. The dried plants were then crushed and passed through a 60-mesh sieve. After 0.60 g of the screened P. notoginseng powder was weighed, it was placed in a 50 mL centrifuge tube, covered with 50 mL of a 75% methanol solution, and then subjected to ultrasound extraction at 60 °C for 45 min. After shaking it for 40 min and leaving it overnight, it was ultrasonically extracted again the following day. After cooling, it was weighed and replenished with 75% methanol before being filtered through a 0.45 µm organic filter membrane into a 2.00 mL sample injection bottle, forming the sample solution used to test the P. notoginseng saponin. For the chromatographic analysis, a 250 mm × 4.6 mm, 5 µm Agilent C18 column was utilized, with a column temperature of 30 °C, a DAD detector, a wavelength of 203 nm, mobile phase A: ultrapure water, and mobile phase B: acetonitrile. The flow rate was set at 1.00 mL min⁻¹, with an injection volume of 10.00 µL [6,7].

2.4. TOPSIS Model

TOPSIS is a decision analysis method for solving multiple objectives. The calculation steps of the TOPSIS method were based on the research of Li and Seyedmohammadi [6,37].

Step 1. Establishing a performance decision matrix A_ij:

$$A_{ij}=\left[\begin{array}{ccc}{a}_{11}& \cdots & a_{1n}\\ ⋮& \ddots & ⋮\\ a_{m1}& \cdots & a_{mm}\end{array}\right];i=\left(1,2\cdots ,m\right);j=\left(1,2\cdots ,n\right)$$

(5)

where a_ij is the j-th evaluation index in the i-th treatment, m = 12, and n = 9.

Step 2. The normalized value b_ij and decision matrix B_ij are calculated as follows:

$$b_{ij}=\frac{a_{ij}}{\sqrt{\left({\displaystyle \sum _{i=1}^m{a}_{ij}^2}\right)}}$$

(6)

$$B_{ij}=\left[\begin{array}{ccc}{b}_{11}& \cdots & b1n\\ ⋮& \ddots & ⋮\\ b_{m1}& \cdots & b_{mn}\end{array}\right]$$

(7)

Step 3. Calculating the weighted normalized decision matrix Z_ij. The calculation method is as follows:

$$Z_{ij}=B_{ij}\times W_{n\times n}=\left[\begin{array}{ccc}{z}_{11}& \cdots & z_{1n}\\ ⋮& \ddots & ⋮\\ z_{m1}& \cdots & z_{mn}\end{array}\right]$$

(8)

$${\displaystyle \sum _{j=1}^n{w}_j=1}$$

(9)

where w_j is the j-th criterion’s weight.

Step 4. Determining the positive ideal (Z_j⁺) and negative ideal (Z_j⁻) solutions:

$$Z_j^{+}=\left\{\begin{array}{l}\max z_{ij}\cdots \cdots j=J\\ \min z_{ij}\cdots \cdots j=J^{\prime }\end{array}\right.$$

(10)

$$Z_j^{-}=\left\{\begin{array}{l}\min z_{ij}\cdots \cdots j=J\\ \max z_{ij}\cdots \cdots j=J^{\prime }\end{array}\right.$$

(11)

where J and J′ are the sets of criteria “with a positive effect” and criteria “with a negative effect”, respectively.

Step 5. Using the m-dimensional Euclidean distance to calculate the separation measures of each alternative from the positive (D_i⁺) and negative (D_i⁻) ideal solutions:

$$D_i^{+}=\sqrt{{\displaystyle \sum _{j=1}^n{\left(z_{ij}-z_j^{+}\right)}^2}}$$

(12)

$$D_i^{-}=\sqrt{{\displaystyle \sum _{j=1}^n{\left(z_{ij}-z_j^{-}\right)}^2}}$$

(13)

Step 6. Calculating the relative closeness to the ideal solution and ranking it:

$$C{I}_i=\frac{D_i^{-}}{D_i^{+}+D_i^{-}}\cdots \cdots \left(0\le c{i}_i\le 1\right)$$

(14)

The CI_i value was used to rank each treatment. In descending order, options were ranked based on their CI_i value.

2.5. Statistical Analysis

Using SPSS 26 software, experimental data were processed and subjected to variance analysis (ANOVA). The significance of data differences was analyzed using the Duncan method. Excel 2019 was used for data processing and TOPSIS model construction. Origin 2018 was used for plotting. Figure 2 shows the flow chart of the research steps carried out in this study.

3. Results

3.1. Effects of Irrigation and Soluble Organic Fertilization on the Growth and Physiology of P. notoginseng

The root of P. notoginseng is mainly used for medicinal purposes. In this study, the F₃ treatment had the highest values of root length, surface area, average diameter, and root volume under the same irrigation level, whereas the W₂ and W₃ treatments had the highest values under the same fertilization level. In the W₁ treatment, there was no significant difference in root length across treatments. Among the other irrigation treatments, the F₃ treatment had much longer roots than the others. There was no statistically significant difference in root surface area between F₁ and F₂ under W₂ and W₃ circumstances. F₃ and F₄ had no significant difference under the same irrigation circumstances. There was no significant change in root volume between the F₂, F₃, and F₄ treatments under W₁. There was no significant change in the average diameter and root volume across irrigation treatments under F₄ conditions. It was worth noting that when irrigation and fertilization were combined, the root morphological characteristics (root length, surface area, average diameter, and volume of root) of the W₂F₃ treatment were significantly higher than those of the W₃F₃ treatment, increasing by 3.13%, 22.52%, 7.10%, and 15.85%, respectively (Figure 3).

Table 2. The effects of various irrigation and soluble organic fertilization levels on the net photosynthetic rate and transpiration rate of P. notoginseng.

Treatments		Net Photosynthetic Rate (μmol·m−2·s−1)				Transpiration Rate (mmol m−2 s−1)
Irrigation Level (W)	Soluble Organic Fertilization Level (F)	Seedling Stage	Budding Stage	Flowering Stage	Fruiting Stage	Seedling Stage	Budding Stage	Flowering Stage	Fruiting Stage
W1	F1	0.44 ± 0.02 f	0.48 ± 0.01 i	3.36 ± 0.09 c	0.76 ± 0.04 e	0.38 ± 0.00 e	0.26 ± 0.00 h	0.38 ± 0.00 j	0.32 ± 0.00 k
	F2	0.44 ± 0.01 f	0.6 ± 0.00 h	3.53 ± 0.04 b	0.87 ± 0.05 e	0.26 ± 0.00 g	0.28 ± 0.00 gh	0.36 ± 0.00 k	0.31 ± 0.00 l
	F3	0.48 ± 0.01 f	1.11 ± 0.01 d	2.91 ± 0.05 e	1.18 ± 0.02 d	0.26 ± 0.00 g	0.31 ± 0.00 g	0.36 ± 0.00 k	0.38 ± 0.00 j
	F4	0.75 ± 0.01 c	1.11 ± 0.01 d	3.13 ± 0.02 d	1.47 ± 0.01 b	0.31 ± 0.00 f	0.38 ± 0.00 f	0.40 ± 0.00 i	0.42 ± 0.00 h
W2	F1	0.63 ± 0.02 d	0.66 ± 0.01 g	2.98 ± 0.07 e	1.14 ± 0.04 d	0.41 ± 0.03 e	0.48 ± 0.01 cd	0.42 ± 0.00 h	0.40 ± 0.00 i
	F2	0.84 ± 0.00 b	1.11 ± 0.01 d	3.52 ± 0.01 b	1.49 ± 0.04 b	0.47 ± 0.01 cd	0.58 ± 0.00 a	0.49 ± 0.00 g	0.45 ± 0.01 g
	F3	0.85 ± 0.00 b	1.4 ± 0.00 c	3.71 ± 0.08 a	1.78 ± 0.05 a	0.45 ± 0.02 d	0.45 ± 0.02 e	0.51 ± 0.00 f	0.48 ± 0.00 f
	F4	0.66 ± 0.03 d	0.72 ± 0.01 f	3.36 ± 0.00 c	1.32 ± 0.07 c	0.50 ± 0.0 bc	0.45 ± 0.02 de	0.59 ± 0.00 d	0.53 ± 0.00 d
W3	F1	0.56 ± 0.01 e	0.82 ± 0.00 e	2.91 ± 0.03 e	1.33 ± 0.01 c	0.58 ± 0.00 a	0.5 ± 0.00 bc	0.70 ± 0.00 a	0.64 ± 0.00 c
	F2	0.78 ± 0.00 c	1.8 ± 0.01 a	3.2 ± 0.01 d	1.15 ± 0.02 d	0.58 ± 0.00 a	0.58 ± 0.00 a	0.66 ± 0.00 b	0.50 ± 0.00 e
	F3	0.92 ± 0.00 a	1.76 ± 0.02 b	3.66 ± 0.03 ab	1.88 ± 0.05 a	0.52 ± 0.02 b	0.51 ± 0.01 b	0.57 ± 0.00 e	0.73 ± 0.00 b
	F4	0.55 ± 0.05 e	0.84 ± 0.00 e	2.92 ± 0.03 e	1.86 ± 0.01 a	0.53 ± 0.01 b	0.53 ± 0.01 b	0.62 ± 0.00 c	0.87 ± 0.00 a
Source of variance
W		**	**	**	**	**	**	**	**
F		**	**	**	**	**	**	**	**
W × F		**	**	**	**	**	**	**	**

The data represent the average of three replicates. “Means ± standard deviation” inside columns followed by various lowercase letters indicate significance in each treatment at the 0.05 level; significant at ** p < 0.01. W₁, W₂, and W₃ represent irrigation amounts of 10, 15, and 20 mm; F₁, F₂, F₃, and F₄ represent soluble organic fertilizer amounts of 60, 90, 120, and 150 kg ha⁻¹.

shows that irrigation levels and soluble organic fertilization levels had significant (p < 0.05) effects on the net photosynthetic rate and transpiration rate. At the seedling, budding, flowering, and fruiting stages, the net photosynthetic rate was highest under F₃ fertilization, followed by F₂, F₄, and F₁. On the other hand, the transpiration rate was highest under F₄ fertilization, followed by F₃, F₂, and F₁ at these same growth stages. Under the F₃ fertilization level, the maximum net photosynthetic rate appeared at the flowering stage, with no significant difference between the W₂ and W₃ net photosynthetic rates. The transpiration rate was highest under the W₃ treatment at the same fertilization level. Compared to the W₁F₁ treatment, the seedling, budding, flowering, and fruiting stages of P. notoginseng showed that under the W₃F₃ treatment, the net photosynthetic rate significantly increased by 106.66%, 269.30%, 9.11%, and 147.99%, respectively, due to the interaction between irrigation and fertilization. Under the W₃F₄ treatment, the transpiration rate significantly increased by 38.53%, 98.75%, 63.47%, and 168.33% at the seedling, budding, flowering, and fruiting stages, respectively, compared to W₁F₁.

In addition, W₃F₃ treatment could promote plant height and stem diameter growth. W₂F₃ treatment could significantly improve the water conductivity of the plant canopy (p < 0.05) (Figure 3 and Figure 4,

Table 3. The effects of various irrigation and soluble organic fertilization levels on canopy hydraulic conductivity characteristics of P. notoginseng.

Treatments		Canopy Hydraulic Conductivity (10−6 kg s−1 MPa−1)
Irrigation Level (W)	Soluble Organic Fertilization Level (F)	Seedling Stage	Fruiting Stage
W1	F1	0.81 ± 0.01 h	2.88 ± 0.04 i
	F2	0.82 ± 0.01 h	3.12 ± 0.03 hi
	F3	1.02 ± 0.00 g	3.20 ± 0.10 h
	F4	1.27 ± 0.04 f	3.91 ± 0.10 g
W2	F1	1.75 ± 0.07 e	4.81 ± 0.17 f
	F2	2.22 ± 0.03 b	5.61 ± 0.01 b
	F3	2.31 ± 0.03 b	6.89 ± 0.10 a
	F4	2.04 ± 0.08 c	5.59 ± 0.12 b
W3	F1	1.82 ± 0.06 de	4.91 ± 0.06 ef
	F2	2.46 ± 0.05 a	5.44 ± 0.12 bc
	F3	2.18 ± 0.06 b	5.21 ± 0.09 cd
	F4	1.89 ± 0.01 d	5.14 ± 0.07 de
Source of variance
W		**	**
F		**	**
W × F		**	**

The data represent the average of three replicates. “Means ± standard deviation” inside columns followed by various lowercase letters indicate significance in each treatment at the 0.05 level; significant at ** p < 0.01. W₁, W₂, and W₃ represent irrigation amounts of 10, 15, and 20 mm; F₁, F₂, F₃, and F₄ represent soluble organic fertilizer amounts of 60, 90, 120, and 150 kg ha⁻¹.

).

3.2. Effects of Various Irrigation and Soluble Organic Fertilization Levels on Dry Matter, Yield, IWP, and PFP of P. notoginseng

The yield was significantly affected by irrigation, fertilization, and their interaction (p < 0.05) (Figure 5). Under W₁, there was no significant difference in yield among treatments F₁, F₂, and F₃. Likewise, the yield difference between F₃ and F₄ under the W₂ condition was not statistically significant, but it was significantly higher than that of the other two fertilizer treatments. The yield was substantially higher under F₄ than the other three treatments under W₃. Interestingly, there was no substantial variation in yield between W₁ and W₃ with F₁, F₂, and F₃.

Irrigation, fertilization, and their interactions all had a substantial (p < 0.05) influence on IWP (Figure 5). There was no discernible difference in IWP between F₁, F₂, and F₃ for W₁. When compared to the other treatments, IWP was much greater with F₄. Similarly, no significant variation in IWP was discovered between F₃ and F₄ for W₂. Under W₃, however, IWP was much greater with F₄ than with the other three treatments.

The PFP was significantly affected by irrigation and fertilization (p < 0.05) (Figure 5). Interestingly, there was no significant interaction between these variables that affected PFP (p > 0.05). Under identical irrigation circumstances, the PFP of the F₁ treatment was substantially higher in comparison to that of the others. However, there was no significant difference in PFP between W₁ and W₂ when under F₁, F₂, and F₃ levels.

Furthermore, irrigation, fertilization, and their interactions significantly affected the underground weight, aboveground weight, root:shoot ratio, and root drying rate (p < 0.05) (

Table 4. The effects of various irrigation and soluble organic fertilization levels on dry matter accumulation of P. notoginseng.

Treatments		Underground (kg ha−1)	Aboveground (kg ha−1)	Root–Shoot Ratio	Root Drying Rate (%)
Irrigation Level (W)	Soluble Organic Fertilization Level (F)
W1	F1	1452.00 ± 41.97 g	638.00 ± 11.64 fg	2.28 ± 0.05 d	0.33 ± 0.01 ab
	F2	1493.07 ± 31.76 g	640.93 ± 15.31 fg	2.33 ± 0.01 d	0.31 ± 0.01 bc
	F3	1431.47 ± 60.45 g	589.60 ± 22.58 g	2.43 ± 0.11 cd	0.30 ± 0.00 bc
	F4	1765.87 ± 13.99 ef	730.40 ± 17.78 e	2.42 ± 0.04 cd	0.32 ± 0.01 bc
W2	F1	1840.67 ± 22.91 def	767.07 ± 19.07 de	2.40 ± 0.05 cd	0.32 ± 0.02 bc
	F2	1874.40 ± 61.6 de	737.73 ± 10.58 e	2.54 ± 007 bcd	0.33 ± 0.01 ab
	F3	2202.93 ± 36.05 c	724.53 ± 6.39 e	3.04 ± 0.07 a	0.35 ± 0.01 a
	F4	2505.07 ± 47.55 b	906.40 ± 17.6 bc	2.76 ± 0.01 b	0.36 ± 0.01 a
W3	F1	1677.87 ± 54.86 f	718.67 ± 57.39 ef	2.36 ± 0.16 cd	0.30 ± 0.01 c
	F2	1997.60 ± 105.14 d	830.13 ± 27.16 cd	2.40 ± 0.05 cd	0.31 ± 0.01 bc
	F3	2431.73 ± 36.05 b	938.67 ± 37.19 b	2.60 ± 0.14 bc	0.33 ± 0.00 ab
	F4	3198.80 ± 71.67 a	1057.47 ± 35.6 a	3.03 ± 0.03 a	0.33 ± 0.01 ab
Source of variance
W		**	**	**	**
F		**	**	**	*
W × F		**	**	**	*

The data represent the average of three replicates. “Means ± standard deviation” inside columns followed by various lowercase letters indicate significance in each treatment at the 0.05 level; significant at ** p < 0.01, significant at * p < 0.05. W₁, W₂, and W₃ represent irrigation amounts of 10, 15, and 20 mm; F₁, F₂, F₃, and F₄ represent soluble organic fertilizer amounts of 60, 90, 120, and 150 kg ha⁻¹.

).

3.3. Effects of Various Irrigation and Soluble Organic Fertilization Levels on the Content of P. notoginseng saponins (PNS)

This study investigated irrigation and fertilization’s impact on notoginsenoside R₁, ginsenosides (R_g1, R_e, R_b1, and R_d), and total P. notoginseng saponins (PNS). The results showed that both irrigation and fertilization, as well as their interaction, had significant effects on R₁, R_g1, R_b1, R_d, and total PNS (p < 0.05). However, R_e had no significant response to water–fertilizer coupling (p > 0.05), although irrigation and fertilization separately had significant effects (p < 0.05) (

Table 5. The effects of various irrigation and soluble organic fertilization levels on the accumulation of effective ingredients in roots of P. notoginseng.

Treatments		R1 (%)	Rg1 (%)	Re (%)	Rb1 (%)	Rd (%)	Total PNS (%)
Irrigation Level (W)	Soluble Organic Fertilization Level (F)
W1	F1	2.28 ± 0.10 d	8.99 ± 0.11 bcde	1.20 ± 0.10 abc	2.26 ± 0.13 f	1.19 ± 0.01 e	15.92 ± 0.37 cde
	F2	1.46 ± 0.04 e	16.20 ± 0.55 a	1.01 ± 0.16 abc	2.30 ± 0.09 f	0.76 ± 0.07 f	21.74 ± 0.53 ab
	F3	1.72 ± 0.06 e	9.25 ± 0.47 bcde	0.30 ± 0.02 d	2.23 ± 0.07 f	1.84 ± 0.04 cd	15.35 ± 0.46 de
	F4	1.76 ± 0.04 e	9.74 ± 0.36 bc	0.19 ± 0.01 d	2.35 ± 0.04 f	0.82 ± 0.05 f	14.86 ± 0.39 de
W2	F1	3.67 ± 0.17 bc	6.14 ± 0.45 cdef	1.11 ± 0.05 abc	3.17 ± 0.17 de	2.72 ± 0.16 a	16.81 ± 0.27 cd
	F2	4.03 ± 0.34 b	9.95 ± 3.74 b	0.99 ± 0.33 bc	2.35 ± 0.14 f	2.12 ± 0.07 b	19.44 ± 3.66 bc
	F3	4. 88 ± 0. 16 a	13. 92 ± 0. 69 a	1. 52 ± 0. 11 ab	2.58 ± 0.15 ef	2.03 ± 0.04 bc	24.94 ± 0.87 a
	F4	3.48 ± 0.30 c	9.56 ± 0.45 bcd	1.57 ± 0.37 a	3.36 ± 0.18 d	1.69 ± 0.14 d	19.66 ± 1.23 bc
W3	F1	1.54 ± 0.06 e	4.73 ± 0.56 f	0.96 ± 0.13 bc	3.60 ± 0.36 d	1.12 ± 0.06 e	11.95 ± 0.56 e
	F2	0.77 ± 0.05 f	5.52 ± 0.22 ef	0.99 ± 0.07 bc	5.48 ± 0.27 b	1.23 ± 0.08 e	13.99 ± 0.43 de
	F3	0.74 ± 0.02 f	5.94 ± 0.05 def	0.86 ± 0.11 c	6.36 ± 0.54 a	1.09 ± 0.09 e	14.98 ± 0.52 de
	F4	1.32 ± 0.21 e	5.72 ± 0.26 ef	1.20 ± 0.13 abc	4.57 ± 0.17 c	1.14 ± 0.10 e	13.96 ± 0.31 de
Source of variance
W		**	**	**	**	**	**
F		*	**	NS	*	**	**
W × F		**	**	**	**	**	**

The data represent the average of three replicates. “Means ± standard deviation” inside columns followed by various lowercase letters indicate significance in each treatment at the 0.05 level; “NS” means no significant; significant at ** p < 0.01, significant at * p < 0.05. The total P. notoginseng saponins (PNS) are the sum of the five saponin contents. W₁, W₂, and W₃ represent irrigation amounts of 10, 15, and 20 mm; F₁, F₂, F₃, and F₄ represent soluble organic fertilizer amounts of 60, 90, 120, and 150 kg ha⁻¹.

). In addition, the study discovered that R₁ was not significantly different among F₂, F₃, and F₄ under the W₁ condition. However, the F₃ treatment outperformed the other treatments under W₂. Under W₃, R₁ did not differ significantly between F₁ and F₄, nor between F₂ and F₃. Furthermore, R_g1, R_e, and R_d showed no significant differences among fertilization treatments under W₃. Irrigation treatments under F₁ and F₂ did not differ significantly in R_e, and fertilization treatments under the W₁ condition did not differ significantly in R_b1. Finally, the total saponin contents of fertilization treatments under W₃ did not differ significantly from one another. The water–fertilizer coupling produced the highest total saponin content under the W₂F₃ at 24.94% (Table 5).

3.4. Comprehensive Assessment

A comprehensive analysis was necessary because there were several best practices for the saponin content as well as for yield, IWP, PFP, and yield. To analyze 12 various irrigation and soluble organic fertilization levels, the TOPSIS model was employed along with yield, IWP, PFP, R₁, R_g1, R_e, R_b1, R_d, and total PNS as evaluation indices. The comprehensive evaluation indexes were 0.442, 0.334, 0.302, 0.540, 0.527, 0.646, 0.541, 0.304, 0.342, 0.361, and 0.363. The comprehensive evaluation of each treatment was W₂F₃ > W₂F₄ > W₂F₁ > W₂F₂ > W₁F₂ > W₁F₁ > W₃F₄ > W₃F₃ > W₃F₂ > W₁F₃ > W₃F₁ > W₁F₄ (

Table 6. TOPSIS analysis of yield, IWP, PFP and PNS.

Treatments		Comprehensive Index									D+	D−	CI	Ranking
Irrigation Level (W)	Organic Fertilization Level (F)	Yield	IWP	PFP	R1	Rg1	Re	Rb1	Rd	Total PNS
W1	F1	0.029	0.039	0.045	0.024	0.030	0.035	0.021	0.023	0.030	0.065	0.049	0.429	6
	F2	0.031	0.041	0.031	0.015	0.054	0.029	0.021	0.015	0.042	0.070	0.055	0.442	5
	F3	0.032	0.042	0.024	0.018	0.031	0.009	0.020	0.036	0.029	0.076	0.038	0.334	10
	F4	0.035	0.047	0.022	0.019	0.033	0.006	0.021	0.016	0.028	0.084	0.036	0.302	12
W2	F1	0.031	0.028	0.048	0.039	0.021	0.032	0.029	0.053	0.032	0.055	0.064	0.540	3
	F2	0.036	0.032	0.037	0.043	0.033	0.029	0.021	0.042	0.037	0.053	0.059	0.527	4
	F3	0.040	0.035	0.031	0.052	0.047	0.044	0.024	0.040	0.048	0.043	0.078	0.646	1
	F4	0.039	0.035	0.024	0.037	0.032	0.046	0.031	0.033	0.038	0.052	0.061	0.541	2
W3	F1	0.028	0.018	0.042	0.016	0.016	0.028	0.033	0.022	0.023	0.079	0.035	0.304	11
	F2	0.030	0.020	0.031	0.008	0.018	0.029	0.050	0.024	0.027	0.077	0.040	0.342	9
	F3	0.034	0.022	0.026	0.008	0.020	0.025	0.058	0.021	0.029	0.078	0.044	0.361	8
	F4	0.041	0.027	0.025	0.014	0.019	0.035	0.042	0.022	0.027	0.073	0.041	0.363	7
Weight W		0.119	0.115	0.115	0.097	0.109	0.107	0.115	0.108	0.115
Positive ideal solution Z+		0.041	0.047	0.048	0.052	0.054	0.046	0.058	0.053	0.048
Negative ideal solution Z−		0.028	0.018	0.022	0.008	0.016	0.006	0.020	0.015	0.023

D⁺: positive ideal distance, D⁻: negative ideal distance, CI: the comprehensive index, W: weight, Z⁺: positive ideal solution, Z⁻: negative ideal solution.

).

The outcome showed that the W₂F₃ treatment could balance yield, IWP, PFP, R₁, R_g1, R_e, R_b1, R_d, and total PNS and had the greatest overall effect for P. notoginseng. The TOPSIS model evaluation findings and the comparative examination of data from multiple variables indicated that the W₂F₃ treatment was the most effective combination of irrigation and soluble organic fertilization.

4. Discussion

Although water absorption and nutrient absorption are two distinct processes, they affect the soil’s physical and chemical characteristics and the physiological functions of plants. Therefore, the relationship between crop water and nutrient absorption is close and complex [38]. To enhance crop productivity and fertilizer utilization rates, the coupling of irrigation and fertilization is a method that emphasizes the organic relationship between water and fertilizer. By capitalizing on the synergistic effect between them, this method helps manage water, fertilizer, and crops [39]. Various studies indicated that moderate irrigation and fertilization led to improvements in the physiological and ecological traits of crops, resulting in increased dry matter accumulation, yield, and quality [40,41,42,43]. In this study, to balance output and quality, a water and fertilizer control approach was proposed. Moderate irrigation and fertilization efficiently enhanced the morphology of the root, yield, and saponin contents during the production phase. The data presented in Table 3, Table 4 and Table 5 and Figure 3 and Figure 4 support these theories.

4.1. Effects of Irrigation and Fertilization on the Growth and Physiology

Due to the higher requirements for water and fertilizer in the cultivation of P. notoginseng, a more accurate water and fertilizer management model was needed. This study found that the plant height, stem diameter, photosynthetic characteristics, and canopy hydraulic conductivity of P. notoginseng increased to the maximum level under W₃ treatment (Table 2 and Table 3, Figure 3 and Figure 4). This phenomenon was mainly due to insufficient irrigation. It was reported that insufficient irrigation would affect cell elongation and mitosis, reduce water movement through the xylem and adjacent cells, and reduce the number and area of leaves, all of which hinder the normal growth of crops [44,45]. Additionally, stomatal closure caused by water stress prevented the expansion of the net photosynthetic area, reduced the photosynthetic rate per unit leaf area, and inhibited photosynthesis and carbon dioxide assimilation, ultimately reducing photosynthetic efficiency [7,45,46]. It was worth noting that the F₄ treatment had a lower net photosynthetic rate than the other treatments. The decrease in the photosynthetic capacity of plant mesophyll cells caused by excessive fertilizer was a possible reason for this phenomenon [47]. Nitrogen stress could lower the chlorophyll content and net photosynthetic rate, compromising photosynthetic function [48,49]. Phosphorus stress could inhibit the synthesis of chlorophyll and cause a decrease in the net photosynthetic rate [50]. Similarly, some of the values in the W₃ treatment exhibited a lower net photosynthetic rate than the other treatments. This individual difference might be associated with the formation of waterlogging stress, whereby the photosynthetic system and chlorophyll synthesis were impacted, decreasing the net photosynthetic rate [51,52]. Furthermore, this deviation mainly arose in high water and fertilizer treatments, which might be assigned to a fall in light saturation point caused by a rise in temperature, leading to a decrease in net photosynthetic rate during measurement [53]. The root is the most critical part affecting the growth of P. notoginseng. Under W₂ treatment, the roots of P. notoginseng had the best morphology. Because the roots of P. notoginseng were very sensitive to changes in soil moisture, sufficient water promoted their growth and development [8]. Moreover, under F₃ treatment, the plant height and stem diameter, root morphological characteristics, net photosynthetic rate, and canopy hydraulic conductivity of P. notoginseng reached their highest levels with the increased fertilization amount. Appropriate fertilization could promote the growth of P. notoginseng by improving the environment around the roots, promoting plant root development, enhancing root activity, and improving crop osmotic and stomatal regulation, which increased the photosynthetic rate to support crop growth [54,55,56,57]. Phosphorus also influences the metabolic functions of plants, including cell division and development, photosynthesis, and respiration, promoting plant growth through these processes [58,59]. Furthermore, sufficient nitrogen levels in organic fertilizers increase the activity of photosynthetic enzymes in chloroplasts, and the amount of carbon dioxide emitted from the soil significantly increases, thereby improving the photosynthesis rate of crops [60,61,62,63]. Organic fertilizers might have also stimulated nitrogen-fixing bacteria and increased yield by promoting the secretion of plant hormones such as gibberellic acid and acetic acid [64,65]. The study by Zhong also showed that long-term application of organic fertilizers could increase the variety and activity of soil microorganisms, promoting crop growth [66].

4.2. Effects of Irrigation and Fertilization on Dry Matter, Yield, IWP, and PFP

Dry matter accumulation is a crucial factor for crop yield [67]. Recent studies have shown that low-level irrigation may harm dry matter accumulation, while higher fertilization levels tend to contribute to increased dry matter accumulation [68]. This study confirmed previous research, showing that the maximum dry matter was achieved under W₃ treatment (Table 4). Low soil moisture content might be the reason for the decline in dry matter accumulation, as it causes stomata closure, leaf cell damage, and reduced photosynthesis [7]. It is clear from previous studies that reasonable water and fertilizer inputs are necessary for improving crop yield and water–fertilizer productivity. For example, Liao discovered that low soil moisture concentration lowered P. notoginseng production considerably [8]. According to the findings of this study, higher dry matter buildup increased P. notoginseng production, which peaked under W₂ and W₃ conditions (Figure 5). Thus, within a certain range of water and fertilizer inputs, the yield tended to increase as irrigation and fertilization increased [30,69,70]. Furthermore, the outcomes of this investigation demonstrated that increased irrigation volume resulted in lower IWP (Figure 5), corroborating the findings by Ali [71]. This phenomenon might be due to increased evapotranspiration resulting in a lower IWP [72]. Additionally, the results indicated that PFP decreased with increasing fertilization (Figure 5), consistent with the findings of Wang and Peng [73,74]. This could be due to the diminishing marginal returns of yield with increasing fertilizer application [75]. As a result, rational water and fertilizer inputs might boost crop yield and water–fertilizer productivity in P. notoginseng production.

4.3. Effects of Irrigation and Fertilization on Saponin Content

Secondary metabolites, which represent active ingredients in Chinese herbal medicine, could be increased in P. notoginseng through the provision of adequate water, nitrogen, and potassium [76,77,78]. The highest content of R_g1 was found in this study, and the overall concentration of ginsenosides R_g1 and R_b1 and notoginsenoside R₁ was not less than 5.0%, which was in agreement with the standard for P. notoginseng saponins [6]. The maximum amounts of notoginsenoside R₁, ginsenosides R_g1, R_e, and R_d, and total saponin were obtained under W₂ treatment, while the total saponin content initially increased and then decreased with increasing irrigation volume. Similar research suggested that the amount of soil water affected the active ingredients in P. notoginseng differently and that under extreme water scarcity, the accumulation of active ingredients decreased [11,79]. Irrigation had a greater effect on the synthesis of notoginsenoside R₁ and ginsenosides R_g1, R_e, R_b1, and R_d, indicating that saponins were more responsive to water. Adequate soil moisture could optimize the activity of antioxidant enzymes and stabilize the gene expression of essential enzymes required for saponin production, thus facilitating saponin synthesis [80]. Organic fertilizer significantly affected the contents of notoginsenoside R₁ and ginsenosides R_g1, R_e, R_b1, and R_d by increasing the number of soil microorganisms, soil porosity, diversity, and organization of the microbial community [81]. Proper irrigation and fertilization practices could enhance the permeability of the soil, stimulate microbial activity, and ultimately increase the saponin content of P. notoginseng [6]. Thus, regulating water and fertilizer was essential for increasing the saponin content of P. notoginseng. According to the TOPSIS model assessment, W₂F₃ showed the best treatment effect for P. notoginseng.

5. Conclusions

Under the conditions of shade and shelter from the rain, the coupling of water and organic fertilizer significantly increased the yield and saponin content of P. notoginseng. Through comprehensive evaluation, we found that the yield and saponin content of the W₂F₃ treatment were the best. The yield of P. notoginseng was 1359 kg ha⁻¹, and the total saponin content was 24.94%. In addition, the coupling effect of water and organic fertilizer treatments could significantly increase plant height, stem diameter, root morphology, photosynthetic characteristics, canopy hydraulic conductivity, dry matter, irrigation water productivity, yield, and quality. Therefore, the combination of irrigation levels (W₂, 15 mm) and soluble organic fertilization levels (F₃, 120 kg ha⁻¹) should be suggested as an appropriate agronomic management method to improve the yield and saponin content of P. notoginseng.