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

: 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 ( W 1 ), 15 ( W 2 ), and 20 ( W 3 ) mm), totaling 440, 660, and 880 mm, and four levels of the total amount of fertilization ( F 1 (60, total N 12.6, total P 5.5, and total K 10.5 kg ha − 1 ), F 2 (90, total N 18.9, total P 8.3, and total K 15.7 kg ha − 1 ), F 3 (120, total N 25.2, total P 11.0, and total K 20.9 kg ha − 1 ), F 4 (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 W 3 F 3 treatment resulted in signiﬁcant increases in the plant’s height, stem diameter, and net photosynthetic rate. Meanwhile, the W 2 F 3 treatment exhibited the best root morphological traits. The W 3 F 4 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 W 2 F 3 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 W 2 F 3 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.


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].

Experimental Design, Field Management, and Agronomic Practices
In this study, the experiment treatments included three levels of irrigation amount (W 1 , W 2 , and W 3 ) with 10, 15, and 20 mm, respectively, and four levels of soluble organic fertilization (F 1 , F 2 , F 3 , and F 4 ) with 60, 90, 120, and 150 kg ha −1 [31,32]. The precise watering and fertilization schedule is shown in Table 1. The experiment was conducted with three replicates for each treatment, randomly distributed within 36 plots. Each plot had an area of 22.8 m 2 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% P 2 O 5 -21% K 2 O + 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 × 10 5 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. farmers in Luxi County. The layout is illustrated in Figure 1. thick were then used to cover the surface of each plot. Oth such as plant trimming, controlling insects, and controlling the help of the local farmers' experience.  (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 drying rate = M 1 /M 0 (2) where M 0 is the wet weight of the underground part, g; M 1 is the dry weight of the underground part, g; and M 2 is the dry weight of the overground part, g. IWP and PFP were calculated as follows [6,36]: 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 .

Saponin Content of P. notoginseng
To determine the content of five saponins (R 1 , 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].

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 : 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: Step 3. Calculating the weighted normalized decision matrix Z ij . The calculation method is as follows: Agronomy 2023, 13, 1742 6 of 20 n ∑ j=1 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: 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: Step 6. Calculating the relative closeness to the ideal solution and ranking it: The CI i value was used to rank each treatment. In descending order, options were ranked based on their CI i value.

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.

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

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 F 3 treatment had the highest values of root length, surface area, average diameter, and root volume under the same irrigation level, whereas the W 2 and W 3 treatments had the highest values under the same fertilization level. In the W 1 treatment, there was no significant difference in root length across treatments. Among the other irrigation treatments, the F 3 treatment had much longer roots than the others. There was no statistically significant difference in root surface area between F 1 and F 2 under W 2 and W 3 circumstances. F 3 and F 4 had no significant difference under the same irrigation circumstances. There was no significant change in root volume between the F 2 , F 3 , and F 4 treatments under W 1 . There was no significant change in the average diameter and root volume across irrigation treatments under F 4 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 W 2 F 3 treatment were significantly higher than those of the W 3 F 3 treatment, increasing by 3.13%, 22.52%, 7.10%, and 15.85%, respectively ( Figure 3).    Table 2 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 F 3 fertilization, followed by F 2 , F 4 , and F 1 . On the other hand, the transpiration rate was highest under F 4 fertilization, followed by F 3 , F 2 , and F 1 at these same growth stages. Under the F 3 fertilization level, the maximum net photosynthetic rate appeared at the flowering stage, with no significant difference between the W 2 and W 3 net photosynthetic rates. The transpiration rate was highest under the W 3 treatment at the same fertilization level. Compared to the W 1 F 1 treatment, the seedling, budding, flowering, and fruiting stages of P. notoginseng showed that under the W 3 F 3 treatment, the net photosynthetic Agronomy 2023, 13, 1742 8 of 20 rate significantly increased by 106.66%, 269.30%, 9.11%, and 147.99%, respectively, due to the interaction between irrigation and fertilization. Under the W 3 F 4 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 W 1 F 1 .

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 W 1 , there was no significant difference in yield among treatments F 1 , F 2 , and F 3 . Likewise, the yield difference between F 3 and F 4 under the W 2 condition was not statistically significant, but it was significantly higher than that of the other two fertilizer treatments. The yield was substantially higher under F 4 than the other three treatments under W 3 . Interestingly, there was no substantial variation in yield between W 1 and W 3 with F 1 , F 2 , and F 3 .
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 F 1 , F 2 , and F 3 for W 1 . When compared to the other treatments, IWP was much greater with F 4 . Similarly, no significant variation in IWP was discovered between F 3 and F 4 for W 2 . Under W 3 , however, IWP was much greater with F 4 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 F 1 treatment was substantially higher in comparison to that of the others. However, there was no significant difference in PFP between W 1 and W 2 when under F 1 , F 2 , and F 3 levels.

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 (Rg1, Re, Rb1, and Rd), and total P. notoginseng saponins (PNS). The results showed that both irrigation and fertilization, as well as their interaction, had significant effects on R1, Rg1, Rb1, Rd, and total PNS (p < 0.05). However, Re had no significant response to water-fertilizer coupling (p > 0.05), although irrigation and fertilization separately had significant effects (p < 0.05) ( Table 5). 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, Rg1, Re, and Rd showed no significant differences among fertilization treatments under W3. Irrigation treatments Figure 5. Effects of various irrigation and soluble organic fertilization levels on yield, irrigation water productivity (IWP), and partial fertilizer productivity (PFP). The data represent the average of three replicates. Error bars represent standard errors. Different letters above the bars indicate significance in each treatment at the 0.05 level. W 1 , W 2 , and W 3 represent irrigation amounts of 10, 15, and 20 mm; F 1 , F 2 , F 3 , and F 4 represent soluble organic fertilizer amounts of 60, 90, 120, and 150 kg ha −1 .

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 R 1 , 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 R 1 , 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). In addition, the study discovered that R 1 was not significantly different among F 2 , F 3 , and F 4 under the W 1 condition. However, the F 3 treatment outperformed the other treatments under W 2 . Under W 3 , R 1 did not differ significantly between F 1 and F 4 , nor between F 2 and F 3 . Furthermore, R g1 , R e , and R d showed no significant differences among fertilization treatments under W 3 . Irrigation treatments under F 1 and F 2 did not differ significantly in R e , and fertilization treatments under the W 1 condition did not differ significantly in R b1 . Finally, the total saponin contents of fertilization treatments under W 3 did not differ significantly from one another. The water-fertilizer coupling produced the highest total saponin content under the W 2 F 3 at 24.94% (Table 5).

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, R 1 , 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 Table 6).
The outcome showed that the W 2 F 3 treatment could balance yield, IWP, PFP, R 1 , 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 W 2 F 3 treatment was the most effective combination of irrigation and soluble organic fertilization. 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. W 1 , W 2 , and W 3 represent irrigation amounts of 10, 15, and 20 mm; F 1 , F 2 , F 3 , and F 4 represent soluble organic fertilizer amounts of 60, 90, 120, and 150 kg ha −1 .

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 Tables 3-5 and Figures 3 and 4 support these theories.

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 W 3 treatment (Tables 2 and 3, Figures 3 and 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 F 4 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 W 3 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 W 2 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 F 3 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].

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 W 3 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 W 2 and W 3 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.

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 R 1 was not less than 5.0%, which was in agreement with the standard for P. notoginseng saponins [6]. The maximum amounts of notoginsenoside R 1 , ginsenosides R g1 , R e , and R d , and total saponin were obtained under W 2 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 R 1 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 R 1 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, W 2 F 3 showed the best treatment effect for P. notoginseng.

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