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. 2025 Aug 29:16:1655710.
doi: 10.3389/fpls.2025.1655710. eCollection 2025.

Optimizing irrigation and fertilization management enhances alfalfa seed yield components through improved soil nutrient availability and leaf photosynthetic efficiency

Jinfeng Hui  1 , Yanliang Sun  1 , Kongqin Wei  1 , Andrew D Cartmill  2 , Ignacio F López  2 , Chunhui Ma  1 , Qianbing Zhang  1
Affiliations

Optimizing irrigation and fertilization management enhances alfalfa seed yield components through improved soil nutrient availability and leaf photosynthetic efficiency

Jinfeng Hui et al. Front Plant Sci. .

Abstract

Introduction: Addressing the challenges of inefficient water-fertilizer utilization and suboptimal seed yield in alfalfa (Medicago sativa L.) seed production systems, we investigated the effects of differential irrigation-fertilization regimes on soil nutrient dynamics, photosynthetic performance, and yield parameters. This study aims to optimize seed production while elucidating the response mechanisms linking soil nutrient availability, foliar photosynthetic efficiency, and seed yield outcomes. This experiment employed drip irrigation to address production constraints in alfalfa seed cultivation.

Methods: Using 'WL354HQ' and 'Xinmu No.4' as the experimental materials, a two-factor randomized block design was adopted, with three fertilization levels: F0 (no fertilizer), F1 (90 kg·ha-1 N 75 kg·ha-1 P2O5, 12 kg·ha-1 K2O), and F2 (120 kg·ha-1 N, 100 kg·ha-1 P2O5, 15 kg·ha-1 K2O), and combined with three irrigation levels W1 (1650 m3·ha-1), W2 (2500 m3·ha-1), and W3 (3350 m3·ha-1).

Results: Water and fertilizer management is a prerequisite for high yield of alfalfa seeds, and the impact of fertilization on seed yield is greater than that of irrigation. Compared to the non-fertilized control (F0W1), the F2W2 treatment significantly increased soil nutrients in the 0-20 cm layer: soil total nitrogen content (+52.17%), total phosphorus content (+18.72%), and organic carbon content (+16.85%), and available phosphorus content (+37.34%), and alkali-hydrolyzable nitrogen content (+17.45%). Notably, F2W2 enhanced net photosynthetic rate by 35.04% despite reduced stomatal conductance (-2.14%) and intercellular CO2 concentration (-9.50%), thereby promoting assimilate partitioning to reproductive organs. Consequently, seed dimensional parameters (width: +53.02%; thickness: +21.75%) and germination rate (+23.11%) were significantly improved (P < 0.05), increasing the seed yields of WL354HQ and Xinmu No.4 by 42.76% and 49.81% respectively. Correlation analysis revealed significant (P < 0.01) positive associations between seed yield and seed length, seed width, seed thickness, chlorophyll a, carotenoids, total chlorophyll content, and net photosynthetic rate. Principal component analysis showed that the optimal fertilization level was N 120 kg·ha-1; P2O5-100 kg·ha-1; K2O 15 kg·ha-1, with an irrigation level of 2500 m3·ha-1 (F2W2) as the optimal model.

Discussion: This optimized model significantly enhanced alfalfa seed yield formation, photosynthetic characteristics, and soil nutrient availability, which provided a theoretical basis for high yield cultivation of alfalfa seed production in arid areas.

Keywords: alfalfa seed production; drip irrigation optimization; photosynthetic efficiency; seed morphology; soil nutrient availability.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Temperature and precipitation during the growth season of alfalfa in 2024.
Figure 2
Figure 2
Effects of water and fertilizer management on SOC, TN, TP, AP and AN contents at different soil depths (0–20 cm, 20–40 cm, and 40–60 cm) of alfalfa. (A–E) SOC denotes soil organic carbon, TN denotes total nitrogen, TP denotes total phosphorus, AP denotes available phosphorus, and AN denotes alkali-hydrolyzable nitrogen contents for alfalfa cultivar WL354HQ. (F–J) SOC denotes soil organic carbon, TN denotes total nitrogen, TP denotes total phosphorus, AP denotes available phosphorus, and AN denotes alkali-hydrolyzable nitrogen contents in for alfalfa cultivar Xinmu No.4. F0 denotes no fertilization, F1 denotes N 90 kg·ha-1; P2O5–75 kg·ha-1; K2O 12 kg·ha-1, F2 denotes N 120 kg·ha-1; P2O5–100 kg·ha-1; K2O 15 kg·ha-1. W1 denotes 1650 m3·ha-1; W2 denotes 2500 m3·ha-1; W3 denotes 3350 m3·ha-1. Uppercase letters denote significant differences (P < 0.05) between irrigation rates within the same fertilization regime. Lowercase letters indicate significant differences (P < 0.05) between fertilization levels within the same irrigation treatment.
Figure 3
Figure 3
Effects of irrigation-fertilization management on Photosynthetic pigment content and photosynthetic performance in alfalfa (WL354HQ and Xinmu No.4). (A) Chla denotes chlorophyll a content, (B) Chlb denotes chlorophyll b content, (C) Car denotes carotenoid content, (D) Ch l(a+b) denotes chlorophyll (a+b) content. Uppercase letters denote significant differences (P < 0.05) between irrigation levels within the same fertilization regime. Lowercase letters indicate significant differences (P < 0.05) between fertilization levels within the same irrigation treatment. ** denotes P < 0.01, * denotes P < 0.05, and ns denotes not significant P ≥ 0.05. WL denotes WL354HQ, XM denotes Xinmu No.4, F F denotes the degree of variation in fertilizer levels, F W denotes the degree of variation in Irrigation levels, F F × F W denotes the degree of variation in the interaction between fertilizer levels and irrigation levels. ** denotes extremely significant differences P < 0.01, * denotes significant differences P < 0.05, and ns denotes not significant P ≥ 0.05.
Figure 4
Figure 4
Effects of irrigation-fertilization management on photosynthetic performance in alfalfa (WL354HQ and Xinmu No.4). (A) Pn denotes net photosynthetic rate, (B) Tr denotes transpiration rate, (C) Gs denotes stomatal conductance, (D) Ci denotes intercellular CO2 concentration. Uppercase letters denote significant differences (P < 0.05) between irrigation levels within the same fertilization regime. Lowercase letters indicate significant differences (P < 0.05) between fertilization levels within the same irrigation treatment. WL denotes WL354HQ, XM denotes Xinmu No.4, F F denotes the degree of variation in fertilizer levels, F W denotes the degree of variation in Irrigation levels, F F × F W denotes the degree of variation in the interaction between fertilizer levels and irrigation levels. ** denotes extremely significant differences P < 0.01, * denotes significant differences P < 0.05, and ns denotes not significant P ≥ 0.05.
Figure 5
Figure 5
Effects of irrigation-fertilization management on growth index of alfalfa (WL354HQ and Xinmu No.4). (A) PH denotes plant height, (B) St denotes stem thick, (C) NPB denotes number of primary branches, (D) NSB denotes number of secondary branches. Uppercase letters denote significant differences (P < 0.05) between irrigation levels within the same fertilization regime. Lowercase letters indicate significant differences (P < 0.05) between fertilization levels within the same irrigation treatment. WL denotes WL354HQ, XM denotes Xinmu No.4, F F denotes the degree of variation in fertilizer levels, F W denotes the degree of variation in Irrigation levels, F F × F W denotes the degree of variation in the interaction between fertilizer levels and irrigation levels. ** denotes extremely significant differences P < 0.01, * denotes significant differences P < 0.05, and ns denotes not significant P ≥ 0.05.
Figure 6
Figure 6
Effects of irrigation-fertilization management on the constituent factors of alfalfa (WL354HQ and Xinmu No.4) seed yield and resource use efficiency. (A) IPRB denotes number of inflorescences per reproductive branch, (B) SFPI denotes number of small flowers per inflorescence, (C) PPI denotes number of pods per inflorescence, (D) SPP denotes seeds per pod, (E) TSW denotes thousand seed weight, (F) PR denotes podding rate, (G) ASY denotes actual seed yield, (H) IWUE denotes irrigation water use efficiency, and (I) PFP denotes partial fertilizer productivity. Uppercase letters denote significant differences (P < 0.05) between irrigation levels within the same fertilization regime. Lowercase letters indicate significant differences (P < 0.05) between fertilization levels within the same irrigation treatment. WL denotes WL354HQ, XM denotes Xinmu No.4, F F denotes the degree of variation in fertilizer levels, F W denotes the degree of variation in Irrigation levels, F F × F W denotes the degree of variation in the interaction between fertilizer levels and irrigation levels. ** denotes extremely significant differences P < 0.01, * denotes significant differences P < 0.05, and ns denotes not significant P ≥ 0.05.
Figure 7
Figure 7
Effects of irrigation-fertilization management on the quality of alfalfa (WL354HQ and Xinmu No.4). (A) GP denotes germination potential, (B) GR denotes germination rate, (C) HR denotes hard seed rate, (D) RL denotes radicle length, (E) EL denotes embryo length, (F) SL denotes seed length, (G) SW denotes seed width, (H) ST denotes seed thickness. Uppercase letters denote significant differences (P < 0.05) between irrigation levels within the same fertilization regime. Lowercase letters indicate significant differences (P < 0.05) between fertilization levels within the same irrigation treatment. WL denotes WL354HQ, XM denotes Xinmu No.4, F F denotes the degree of variation in fertilizer levels, F W denotes the degree of variation in Irrigation levels, F F × F W denotes the degree of variation in the interaction between fertilizer levels and irrigation levels. ** denotes extremely significant differences P < 0.01, * denotes significant differences P < 0.05, and ns denotes not significant P ≥ 0.05.
Figure 8
Figure 8
Pearson correlation analysis showed the relationship between alfalfa (WL354HQ and Xinmu No.4) seed composition factors, photosynthetic performance and yield. The size of the squares shows a significant level, and the color of the squares shows a positive correlation or a negative correlation. P values less than 0.01 and 0.05 are indicated by asterisks and dot symbols “**”, and “*”. The abbreviations used in the figure are: ASY denotes actual seed yield, IPRB denotes number of inflorescences per reproductive branch, SFPI denotes number of small flowers per inflorescence, PPI denotes number of pods per inflorescence, SPP denotes seeds per pod, TSW denotes thousand seed weight, PR denotes podding rate, NPB denotes number of primary branches, NSB denotes number of secondary branches, SL denotes seed length, SW denotes seed width, ST denotes seed thickness, Chla denotes chlorophyll a content, Chlb denotes chlorophyll b content, Car denotes carotenoid content, Ch l(a+b) denotes chlorophyll (a+b) content, Pn denotes net photosynthetic rate, Tr denotes transpiration rate, Gs denotes stomatal conductance, and Ci denotes intercellular CO2 concentration.
Figure 9
Figure 9
Analysis of the influence of irrigation-fertilization management on alfalfa (WL354HQ and Xinmu No.4) seed yield and its correlation with AP and AN contents. (A–D) represents the relationship between alfalfa seed yield and the input amounts of N, P, and K as well as the irrigation volume. (E, F) represents the relationship between alfalfa seed yield and soil AP and AN contents. Polynomial fitting determines that the error zone (shaded area) corresponds to the 95% confidence interval of the relationship, and the red line represents the linear trend line. The abbreviations used in the picture are: Yield denotes seed yield, AP denotes available phosphorus contents, AN denotes alkali-hydrolyzable nitrogen contents.
Figure 10
Figure 10
The correlation between alfalfa (WL354HQ and Xinmu No.4) seed yield and the contents of soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) at different soil depths.
Figure 11
Figure 11
The correlation analysis of Mantel test shows the relationship between alfalfa seed quality, resource use efficiency and photosynthetic performance. The thickness of the line shows the R2 level, the size of the square shows the significant level, and the color of the square shows a positive correlation or a negative correlation. P values less than 0.01 and 0.05 are indicated by asterisks and dot symbols “**”, and “*”. The abbreviations used in the picture are: ASY denotes actual seed yield, IPRB denotes number of inflorescences per reproductive branch, SFPI denotes number of small flowers per inflorescence, PPI denotes number of pods per inflorescence, SPP denotes seeds per pod, TSW denotes thousand seed weight, PR denotes podding rate, NPB denotes number of primary branches, and NSB denotes number of secondary branches.
Figure 12
Figure 12
Principal component analysis and comprehensive score of the measured indicators under irrigation-fertilization management. The abbreviations used in the picture are: SOC denotes soil organic carbon content, TN denotes total nitrogen content, TP denotes total phosphorus content, AP denotes available phosphorus contents, AN denotes alkali-hydrolyzable nitrogen contents, Chla denotes chlorophyll a content, Chlb denotes chlorophyll b content, Car denotes carotenoid content, Ch l(a+b) denotes chlorophyll (a+b) content, Pn denotes net photosynthetic rate, Tr denotes transpiration rate, Gs denotes stomatal conductance, Ci denotes intercellular CO2 concentration, PH denotes plant height, St denotes stem thick, NPB denotes number of primary branches, NSB denotes number of secondary branches, IPRB denotes number of inflorescences per reproductive branch, SFPI denotes number of small flowers per inflorescence, PPI denotes number of pods per inflorescence, SPP denotes seeds per pod, TSW denotes thousand seed weight, PR denotes podding rate, ASY denotes actual seed yield, IWUE denotes irrigation water use efficiency, PFP denotes partial fertilizer productivity, GP denotes germination potential, GR denotes germination rate, HR denotes hard seed rate, RL denotes radicle length, EL denotes embryo length, SL denotes seed length, SW denotes seed width, ST denotes seed thickness.
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