Jujube–Cotton Intercropping Enhances Yield and Economic Benefits via Photosynthetic Regulation in Oasis Agroecosystems of Southern Xinjiang

Abstract

This study aimed to clarify the effects of jujube–cotton intercropping on cotton yield and photosynthetic characteristics, providing a theoretical basis for its application in the oasis irrigation areas of southern Xinjiang and offering practical recommendations to local farmers for increasing economic benefits. The effects were investigated from 2020 to 2023 using Zhongmian 619 cotton and juvenile jujube trees. Changes in leaf area index (LAI), transpiration rate (Tr), stomatal conductance (Gs), net photosynthetic rate (Pn), intercellular CO₂ concentration (Ci), yield, and economic benefits were evaluated over the years. The results showed that (1) a positive correlation was observed between LAI and the photosynthetic characteristics of cotton. Compared to monoculture cotton, intercropped cotton exhibited lower Pn, Gs, and Tr, and at the peak boll stage, monoculture cotton had significantly higher photosynthetic characteristics, indicating that intercropping affected cotton photosynthesis. (2) From 2020 to 2023, the land equivalent ratio (LER) of jujube–cotton intercropping remained above 1, with overall yield and economic benefit surpassing those of monoculture cotton and jujube, particularly in 2023 when the yield increased by 55.35%. (3) A significant positive correlation was found between cotton yield and LAI. In conclusion, jujube–cotton intercropping enhances photosynthesis, improving yield, economic benefits, and land use efficiency.

1. Introduction

Jujube trees (Ziziphus jujuba Mill.) and cotton (Gossypium hirsutum) are two major economic crops in the southern region of Xinjiang [1]. Cotton is the largest agricultural crop in Xinjiang, with the region responsible for more than 80% of China’s total cotton production [2]. As a characteristic economic crop of the region, jujube trees hold significant importance, while southern Xinjiang possesses the largest cotton planting area in the entire Xinjiang region [3]. The agronomic practices in these regions involve extensive monoculture cotton farming, while jujube cultivation predominantly focuses on the growth of young trees in orchards. The cultivation area used for cotton in Xinjiang covers approximately 2.5 million hectares, while jujube is grown on around 150,000 hectares [4]. With the improvement of climatic conditions and advancements in agricultural technology, the cultivation areas of both jujube trees and cotton have been steadily increasing, positively impacting local agricultural development [5]. However, with the expansion of jujube tree cultivation, particularly the large-scale planting of young jujube trees, the issue of land resource wastage has gradually become apparent [6]. In the early growth stage, young jujube trees have small crowns and underdeveloped root systems, making them unable to fully utilize available land resources, which results in idle land and resource wastage [7]. Although the monoculture cotton farming model can provide relatively stable economic returns, it has certain limitations, as prolonged monoculture often results in excessive depletion of soil nutrients and may lead to ecological and environmental problems such as soil degradation and increased incidence of pests and diseases [8,9]. Therefore, optimizing land resource utilization and improving agricultural economic efficiency has become an urgent issue that needs to be addressed [10].

Compared to the monoculture farming model, intercropping can more effectively utilize land resources, improve soil quality, and enhance ecological benefits [11]. The jujube–cotton intercropping system is increasingly being recognized for its role in optimizing land use, enhancing resource efficiency, and contributing to the local economy [12]. Jujube–cotton intercropping optimizes the ecological niches of both crops through rational pairing, thereby enhancing sunlight utilization and improving the microenvironment within the cropping system, which in turn promotes higher photosynthetic efficiency and improves cotton growth, development, and yield [13,14]. Additionally, distinct ecological niches and proper spatial arrangement between jujube trees and cotton minimize resource competition and enhance overall land use efficiency in this intercropping system [15,16]. The heat resources refer to temperatures, with a mean annual temperature of 10.7 °C and a ≥10 °C cumulative temperature of 4113 °C in the experimental area [17]. The practical arrangement of jujube trees and cotton facilitates the optimal allocation of solar energy and water resources, mitigates the negative effects of intense sunlight on cotton, and, consequently, enhances the overall photosynthetic efficiency [18].

Photosynthesis is the fundamental physiological process underlying crop growth and yield production; its efficiency directly affects the growth rate of plants and their yield potential [19]. In the jujube–cotton intercropping system, jujube trees, as taller crops, have canopy structures that can provide partial shading for cotton plants [20]. This helps alleviate the stress caused by intense sunlight, thereby preventing the decline in cotton’s photosynthetic efficiency under high temperatures and strong light [21]. Meanwhile, cotton plants can take advantage of the varying light conditions across different vertical layers, which enhances the photosynthetic efficiency of their leaves, boosts their growth, and further contributes to yield improvements [22]. The proper management of light, water, and nutrients optimizes the crops’ ecological niches, which is beneficial for improving the photosynthetic efficiency and growth potential of cotton, thereby contributing to yield enhancements [23]. By improving the ecological niche relationships between crops, it is possible not only to enhance solar energy utilization but also to increase the overall productivity and economic efficiency of the cropping system [24,25]. In the jujube–cotton intercropping system in southern Xinjiang, cotton, as a light-sensitive annual crop, was susceptible to photosynthetic activity and yield affected by light competition caused by shading of jujube trees [26]. Previous studies have shown that under intercropping conditions, the reduction in light exposure significantly reduces the net photosynthetic rate and biomass accumulation of cotton, which ultimately affects the yield performance [27]. Therefore, understanding the photoresponse characteristics of cotton is of great significance for optimizing the canopy structure and improving crop productivity in such an agroforestry system.

Although the jujube–cotton intercropping system shows potential for improving crops’ photosynthetic efficiency and yield, the relationship between photosynthetic characteristics and yield in intercropped versus monoculture cotton has not been thoroughly investigated in long-term field experiments in the Alar reclamation area. Therefore, in this study, we aim to explore the relationship between the photosynthetic traits and yield of cotton within the jujube–cotton intercropping system in the Alar reclamation area of southern Xinjiang. By conducting a comparative analysis of the photosynthetic performance and yield differences between intercropped and monoculture cotton, we seek to clarify the role of the intercropping model in enhancing solar energy utilization and economic benefits. The ultimate goal is to provide a theoretical foundation and practical guidance for the sustainable development of agriculture in southern Xinjiang.

2. Materials and Methods

2.1. Overview of the Experimental Site

This study was conducted from 2020 to 2023 in the jujube–cotton intercropping experimental field of the Horticultural Experiment Station, Tarim University, located in Aral City, Xinjiang (41°34′ N, 82°17′ E; elevation: 1014 m). The region is characterized by a large diurnal temperature range and abundant sunlight. The accumulated temperatures for 2020, 2021, 2022, and 2023 were 4311.8 °C, 4415.7 °C, 4663.8 °C, and 4545.5 °C, respectively, while annual rainfall for these years was 27.7 mm, 46 mm, 51.5 mm, and 109.46 mm, respectively. The soil in the experimental field is classified as sandy loam. The annual average solar radiation is approximately 5200 MJ/m², with photosynthetically active radiation ranging from 2340 to 2600 MJ/m², and the average daily sunshine duration accounts for about 66% of the day. The meteorological data from 2020 to 2023 are shown in Figure 1.

The site is situated in the middle to upper reaches of the Tarim River. The soil is characterized by relatively low nutrient content, with nitrogen (N), phosphorus (P), potassium (K), and organic matter levels of 0.10%, 0.05%, 0.20%, and 1.5%, respectively. The area is arid, with an average annual evaporation of 1985.6–2567.9 mm and an average annual precipitation of only 40.1–105.2 mm.

2.2. Experimental Design

This experiment was designed as a single-factor randomized block design, consisting of three treatments (Figure 2): cotton (Gossypium hirsutum) monoculture (MC), jujube (Ziziphus jujuba Mill.) monoculture (MJ), and jujube–cotton intercropping (IC). The row spacing configuration for MJ was 3 m; in the IC, cotton was planted 1.0 m from both sides of the jujube trees with 4 rows of cotton, and the row spacing was (20 + 60 + 20 cm); for MC, the row spacing was (66 + 10 cm). A total of three treatments were performed with three replications, resulting in nine plots. Each plot had an area of 8 m × 6 m. The Grey Jujube was selected for the jujube trees, and Zhongmian 619 cotton was chosen as the cotton crop.

The test jujube garden was planted with sour jujube in 2012, grafted with Grey Jujube in 2014, and repaired in 2019. Cotton was planted annually between the rows of jujube trees. The reason for selecting Grey Jujube for intercropping was that it has a small canopy, short growth cycle, and high yield potential, and is suitable for cultivation in southern Xinjiang. Zhongmian 619 was chosen for its long growth period and concentrated boll opening, making it an ideal choice for this experiment. The cotton and jujube plants were harvested around the 20th of October. Field management followed the typical technical regulations of jujube–cotton intercropping in southern Xinjiang. Drip irrigation under the film was applied every 7–10 days at a rate of 45–60 mm per session, adjusted according to moisture conditions, with a total irrigation volume was 750 m³/ha during the whole growth period. Fertilization primarily involved urea, diammonium phosphate and potassium sulfate, with a total application rate of 450 kg/ha based on an N:P₂O₅:K₂O ratio of 2:1:1. Pest control is mainly aimed at cotton bollworm and red spider, spraying emamectin chlorantraniliprole (15%) and avermectin (1.8%) at seedling and early flowering stage, combined with sexual attractants and yellow plate monitoring, depending on the insect condition.

2.3. Measured Parameters

2.3.1. Photosynthetic Parameter Measurement

For all four years of the experiment, measurements were taken during the cotton seedling, bud, full bloom, boll development, and boll opening stages, on clear days. Using a Li-6400 XT portable photosynthesis system (Li-6400, Li-COR Inc., Lincoln, NE, USA), measurements were taken between 11:00 AM and 1:00 PM [28]. For each treatment, three representative cotton plants were selected, and the following parameters were measured: Pn, Gs, Ci, and Tr. For each cotton plant, measurements were taken three times on the third leaf from the top, and the average value was calculated.

2.3.2. Leaf Area Index (LAI) Measurement

During the cotton seedling, bud, full bloom, boll development, and boll opening stages, from 2020 to 2023, LAI was measured under clear weather conditions using an LAI-2200c manufactured by LI-COR Corporation of Lincoln, NE, USA. This was performed to determine the leaf area index (LAI) of intercropped and monoculture cotton [29].

2.3.3. Yield Measurement

During the cotton boll opening stage, the actual harvest yield for each plot was measured. The data were then converted into yield per hectare. For jujube trees, the fruit yield was measured during the harvest period, and the result was also converted to yield per hectare [30].

2.3.4. Land Equivalent Ratio (LER)

The LER is an indicator used to measure the land use efficiency of jujube–cotton intercropping. If the LER is greater than 1, it means that jujube–cotton intercropping is more efficient in utilizing land resources compared to monoculture. The calculation formula is as follows [31]:

$$\mathrm{L}\mathrm{E}\mathrm{R}={\displaystyle \frac{{\mathrm{Y}}_{\mathrm{C}\mathrm{I}}}{{\mathrm{Y}}_{\mathrm{C}\mathrm{M}}}}+{\displaystyle \frac{{\mathrm{Y}}_{\mathrm{J}\mathrm{I}}}{{\mathrm{Y}}_{\mathrm{J}\mathrm{M}}}}$$

(1)

where Y_CI = cotton intercropping yield, Y_JI = jujube intercropping yield, Y_CM = cotton intercropping yield, and Y_IM = jujube monoculture yield.

2.3.5. Yield Advantage

The yield advantage is the relative increase in net yield achieved through intercropping cotton with jujube, compared to that achieved through monocropping either of the crops. It is calculated as the percentage difference in total yield between the intercropping system and the monocropping system, reflecting the net benefit in terms of crop productivity. YAP serves as an indicator of the efficiency and sustainability of intercropping systems in optimizing land use and improving overall agricultural output [32,33]:

$$\mathrm{N}\mathrm{e}\mathrm{t} \mathrm{R}\mathrm{e}\mathrm{c}\mathrm{e}\mathrm{i}\mathrm{p}\mathrm{t}=\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l} \mathrm{I}\mathrm{n}\mathrm{c}\mathrm{o}\mathrm{m}\mathrm{e}-\mathrm{C}\mathrm{o}\mathrm{s}\mathrm{t}$$

(2)

$$\mathrm{Y}\mathrm{i}\mathrm{e}\mathrm{l}\mathrm{d} \mathrm{A}\mathrm{d}\mathrm{v}\mathrm{a}\mathrm{n}\mathrm{t}\mathrm{a}\mathrm{g}\mathrm{e} \mathrm{P}\mathrm{e}\mathrm{r}\mathrm{c}\mathrm{e}\mathrm{n}\mathrm{t}\mathrm{a}\mathrm{g}\mathrm{e}={\displaystyle \frac{\mathrm{N}\mathrm{e}\mathrm{t} \mathrm{R}\mathrm{e}\mathrm{c}\mathrm{e}\mathrm{i}\mathrm{p}\mathrm{t}}{\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l} \mathrm{I}\mathrm{n}\mathrm{c}\mathrm{o}\mathrm{m}\mathrm{e}}}\times 100\mathrm{\%}$$

(3)

2.4. Data Analysis

In this study, significance testing was conducted using SPSS 25 (Statistical Package for the Social Sciences). Pearson’s correlation analysis and Duncan’s multiple-range test were used to analyze the correlations and differences between the groups. The significance of the results was determined based on the p-value (p < 0.05). Additionally, Origin 2021 (OriginLab Corporation’s Data Analysis and Graphing Software) and GraphPad Prism 10 (GraphPad Software’s Statistical Analysis and Graphing Software for Biomedical Research) were employed to create the graphs, providing a visual representation of the relevant analysis results.

3. Results

3.1. The Effect of Jujube–Cotton Intercropping on Cotton Leaf Area Index

The LAI of cotton across the years showed an increasing trend initially, followed by a decrease as the growth cycle progressed, with the maximum value observed during the boll development stage (Figure 3). There were significant differences between the LAI achieved with MC and IC at different stages in different years. Specifically, in 2020, during the budding period, the LAI achieved with MC was 42.9% higher than that achieved with IC. In 2021 (boll period) and 2022 (flowering period), significant differences were observed between the LAI achieved with IC and MC. However, in 2023, there were no significant differences in the LAI achieved with the different treatments. This suggests that intercropping can influence the growth dynamics of cotton, though the effect may vary across years and growth stages.

3.2. The Effect of Jujube–Cotton Intercropping on Cotton Net Photosynthetic Rate

As shown in Figure 4, the Pn of cotton leaves during different growth stages from 2020 to 2023 exhibited a unimodal curve, showing an initial increase followed by a decline. Overall, the Pn achieved with MC was higher than that achieved with IC. In 2021, the Pn achieved with MC was significantly higher than that achieved with IC by 8.9% and 17.84% during the boll and boll opening periods, respectively. In 2022, the Pn achieved with MC was significantly higher than that achieved with IC by 8.69%, 8.36%, and 30.19% during the seeding, boll, and boll opening periods, respectively. In 2023, the Pn achieved with MC was significantly higher than that achieved with IC by 8.66% and 30.85% during the boll and boll opening periods, respectively. These results suggest that, overall, the MC crops exhibited a higher net photosynthetic rate compared to the IC crops, especially during the later growth stages.

3.3. The Effect of Jujube–Cotton Intercropping on Cotton Stomatal Conductance

Stomatal conductance (Gs) refers to the degree of stomatal opening over a given period, directly influencing gas exchange between the plant and its environment and serving as a key factor affecting photosynthesis. The Gs of cotton showed an increasing trend followed by a decrease as the growth cycle progressed, reaching its maximum value during the boll development stage (Figure 5). At all growth stages, the Gs of the MC crops was higher than that of the IC crops. Significant differences were observed between the monoculture and intercropped cotton in different years: in 2020, during the budding and boll opening periods, the Gs of the MC crops was significantly higher than that of the IC crops, by 32.11% and 57.14%, respectively; in 2021, significant differences were observed between the Gs of the IC and MC crops during the boll opening period; in 2022, during the flowering period, there was a significant difference between the IC and MC crops’ Gs values; in 2023, significant differences in the Gs values were observed during the flowering and boll periods. These results indicate that the monoculture cotton generally had a higher stomatal conductance compared to the intercropped cotton, with the difference being more pronounced in certain growth periods and years.

3.4. The Effect of Jujube–Cotton Intercropping on Cotton Intercellular CO₂ Concentration

As shown in Figure 6, the Ci of the cotton leaves during different growth stages from 2020 to 2023 exhibited a decrease followed by an increase. At all growth stages, the Ci values of the IC crops were lower than those of the MC crops. Significant differences in the Ci between the monoculture and intercropped cotton were observed in different years: in 2020, during the boll and boll opening periods, there was a significant difference in the Ci between the MC and IC crops. In 2021, significant differences were observed in the Ci values during the boll and boll opening periods; in 2022, during the flowering and boll opening periods, the difference between the IC and MC crops’ Ci values was extremely significant; in 2023, during the boll period, the Ci of the MC crops was 11.1% lower than that of the IC crops. These findings suggest that intercropped cotton tends to have a higher intercellular CO₂ concentration than monoculture cotton, with the difference being more pronounced in certain years and growth stages.

3.5. The Effect of Jujube–Cotton Intercropping on Cotton Transpiration Rate

As shown in Figure 7, the Tr of cotton throughout the growth period in different years followed a curve, showing an initial increase followed by a decrease. Although the magnitude of the change varied significantly between years, the Tr of cotton reached its maximum value during the flowering and boll development stages. At all growth stages, the Tr of the MC crops was higher than that of the IC crops. Significant differences in the Tr between the monoculture and intercropped cotton were observed in different years: In 2020, during the budding period, there was a significant difference between the MC and IC crops’ Tr values. In 2021, during the seeding and boll opening periods, the Tr of the MC crops was higher than that of the IC crops, by 12.28% and 22.10%, respectively. In 2022 and 2023, during the seeding, budding, and boll opening periods, significant differences in the Tr were observed between the IC and MC crops. These results indicate that the monoculture cotton consistently exhibited a higher transpiration rate compared to that of the intercropped cotton, especially during certain growth periods. The differences in the Tr between the two cropping systems varied across years and growth stages.

3.6. The Effect of Jujube–Cotton Intercropping on Crop Yield and Land Equivalent Ratio

In the jujube–cotton intercropping system, the jujube yield is also a significant component of the overall system yield, while the LER is a core indicator of the system’s productivity. The four-year experimental results indicated that the inclusion of cotton in the intercropping system significantly reduced both the jujube and cotton yields. Compared to the monoculture system, jujube yield under the intercropping system was decreased by 34.9% in 2020, by 20.5% in 2021, by 34.2% in 2022, and by 21.7% in 2023, respectively. However, the LER is an important parameter for assessing the yield advantages of the intercropping system. In all years, the LER for the jujube–cotton intercropping system was greater than 1, indicating that intercropping consistently enhanced the land use efficiency. This suggests that, regardless of the year, the jujube–cotton intercropping system achieved the highest land use efficiency in the three planting systems (intercropping, monoculture cotton, and monoculture jujube). The MC crop yield was consistently higher than that of the IC crops each year. However, the total yield in the jujube–cotton intercropping system was higher than that of the MC or MJ crops. The LER was significantly affected by the planting system as well as by the interaction between the planting system and year, with the planting system itself having a highly significant impact. The results suggest that the planting system’s effect on the LER was greater than the effect of the year on the LER.

3.7. Comparison of Economic Benefit of Different Planting Systems in Different Years

The net profit from both the monoculture cotton and monoculture jujube was lower than that of the jujube–cotton intercropping system. Except for 2022, the net income from jujube was higher than the net income from cotton in the intercropping system. The reason for the lower net income of monoculture jujube in 2022 was due to the fact that it was the jujube orchard’s off-year, and the purchase price for jujube was as low as 6 CNY/kg. Therefore, the economic benefit from jujube was low in that year. Over the four-year period, the net income was generally ranked as follows: IC > MJ > MC. Specifically, the profit margin for the jujube–cotton intercropping system ranged from 35.72% to 49.34%, with a yield advantage of 13.62%; the monoculture cotton had a profit margin ranging from 35.23% to 43.39%, with a yield advantage of 8.16%; the monoculture jujube had a profit margin ranging from 14.14% to 55.36%, with a yield advantage of 41.22%.

3.8. Correlation Analysis Between Cotton Yield and Photosynthetic Characteristics

As shown in Figure 8, there was a significant positive correlation between the cotton yield and photosynthetic characteristics (including leaf area index, net photosynthetic rate, stomatal conductance, and transpiration rate) in all years, with the majority of correlation coefficients exceeding 0.8. This relationship was especially pronounced in the monoculture cotton. Conversely, the correlation between photosynthetic characteristics and yield in the intercropped cotton was generally weaker. Specifically, in 2020 and 2021, the correlation coefficients between the photosynthetic characteristics and the yield of the intercropped cotton were lower compared to the monoculture cotton. Furthermore, over the four consecutive years, the cotton yield showed a significant negative correlation with the intercellular CO₂ concentration. Overall, the results reveal a close relationship between the photosynthetic characteristics and yield. While the intercropping system did not affect the photosynthetic efficiency of cotton, it still contributed to the overall yield increases.

4. Discussion

4.1. Impact on Cotton Yield Efficiency

In the jujube–cotton intercropping system, the year-to-year variability significantly influenced the cotton yield, with the planting pattern and crop growth characteristics being key contributing factors [34]. Except for the year 2023, the cotton yield within the intercropping system showed a declining trend over time, while the jujube tree yield increased steadily (

Table 1. The impact of different cropping patterns on yield and land equivalent ratio (LER).

Year	Cropping Pattern	Cotton (kg/hm2)	Jujube (kg/hm2)	Total (kg/hm2)	LER
2020	IC	3451.3 ± 194.9 b	3235.1 ± 167.8 b	6686.4 ± 352.1 b	1.28 ± 0.01 b
	MC	5469.3 ± 244.8 a	-	-	-
	MJ	-	4972.8 ± 237.9 a	-	-
2021	IC	3338.5 ± 155.6 b	4110.3 ± 156.8 b	7448.8 ± 309.6 a	1.39 ± 0.02 a
	MC	5658.4 ± 402.4 a	-	-	-
	MJ	-	5164.6 ± 145.4 a	-	-
2022	IC	3301.5 ± 270.2 b	3125.1 ± 202.8 b	6426.6 ± 463.8 c	1.28 ± 0.04 b
	MC	5268.2 ± 247.8 a	-	-	-
	MC	-	4751.9 ± 188.3 a	-	-
2023	IC	3641.2 ± 169.6 b	4132.1 ± 200.3 b	7773.3 ± 368.9 a	1.37 ± 0.04 a
	MC	5865.0 ± 454.3 a	-	-	-
	MJ	-	5274.7 ± 360.8 a	-	-
F-value	C	**	**	**	**
	Y	*	*	*	*
	C × Y	**	**	**	**

Note: Within a column, mean values ± standard errors with different lowercase letters indicate significant differences at p < 0.05. C represents the planting pattern, Y represents the year, and C × Y represents the interaction between the planting pattern and year. * p < 0.05; ** p < 0.001. -: no value. IC, MJ, and MC represent jujube–cotton intercropping, jujube monoculture, and cotton monocropping, respectively.

). Although the total yield peaked in 2023, the LER did not reach its highest value, suggesting that the core goal of intercropping—optimizing land use efficiency—was not achieved that year. The LER in 2023 was significantly higher than that in 2020 and 2022, but it did not differ significantly from the peak LER observed in 2021. This indicates that, despite the increased biomass production in 2023, the competition between cotton and jujube may have limited the land use efficiency. The unusually high yield in 2021 and 2023 is closely tied to the increased rainfall in these years, highlighting the critical role of climatic factors in crop productivity. This is particularly relevant in arid and semi-arid regions, where fluctuations in precipitation can have a substantial impact on crop growth and yield outcomes [35,36].

From a yield perspective, although the cotton yield in the jujube–cotton intercropping system was slightly lower than that achieved with the monoculture system, the total yield (including both cotton and jujube) in the intercropping system was significantly higher than that in the monoculture system (Table 1). This suggests that well-designed intercropping configurations can significantly boost the overall land productivity. The increase in the total yield reflects the efficient land use facilitated by the jujube–cotton intercropping system. By integrating both cotton and jujube, the intercropping system maximizes the productive potential of the land by leveraging the complementary relationship between the two crops [37]. This approach results in higher yields per unit area compared to monoculture farming. Notably, excluding the exceptional climatic impact observed in 2022, the jujube–cotton intercropping system demonstrates significantly higher net income and a more stable profit margin compared to monoculture systems (

Table 2. Economic benefits of different cropping patterns in different years.

Year	Cropping Pattern	Total Income (CNY/ha)	Cost (CNY/ha)	Net Receipt (CNY/ha)	Yield Advantage Percentage(%)
2020	IC	46,045.50	26,844.99	19,200.51	41.70
	MC	37,081.85	21,372.04	15,709.81	42.37
	MJ	34,809.60	16,152.68	18,656.92	53.60
2021	IC	54,632.73	29,952.31	24,680.42	45.18
	MC	36,864.48	21,679.3	15,185.18	41.19
	MJ	41,316.80	24,671.21	16,645.59	40.29
2022	IC	40,259.87	25,877.67	14,382.2	35.72
	MC	34,322.32	22,230.24	12,092.08	35.23
	MJ	28,511.40	24,479.31	4032.09	14.14
2023	IC	67,109.47	33,999.54	33,109.93	49.34
	MC	38,210.48	21,632.11	16,578.37	43.39
	MJ	55,384.35	24,731.14	30,653.21	55.35

Note: The prices of cotton from 2020 to 2023 were 6.51 CNY/kg, 10.8 CNY/kg, 7 CNY/kg, and 8.2 CNY/kg, respectively. From 2020 to 2023, the prices of jujube trees were 7.3 CNY/kg, 8 CNY/kg, 6 CNY/kg, and 10.5 CNY/kg, respectively. The cost is calculated according to the market price of materials, seeds, agricultural machinery, drip irrigation, mulch, etc. IC, MJ, and MC represent jujube–cotton intercropping, jujube monoculture, and cotton monocropping, respectively.

). These findings further reinforce the feasibility and superiority of the jujube–cotton intercropping model in agricultural production, offering farmers more sustainable and stable economic returns.

4.2. Relationship Between Photosynthetic Characteristics and Yield

Photosynthesis is a critical physiological process that influences cotton growth and yield [38]. Relevant studies indicate that sunlight availability is one of the key factors affecting cotton growth and yield in the jujube–cotton intercropping system [39]. Jujube trees’ large canopies cast shade on cotton during the later stages of their growth, which can negatively affect cotton’s photosynthetic capacity [40]. The photosynthetic characteristics of cotton in the jujube–cotton intercropping system (such as the LAI, Pn, Gs, and Tr) were lower than those observed in monoculture cotton (Figure 3, Figure 4, Figure 5 and Figure 7). Additionally, these indicators were positively correlated with the yield across different cropping patterns (Figure 8), which is consistent with previous findings [41]. Between 2020 and 2023, the Pn of the intercropped cotton was 8.3–9.4% lower than that of the monoculture cotton (Figure 4). This difference is primarily attributed to the shade cast by the jujube trees, which limits the amount of light available for cotton, thus restricting the efficiency of photosynthesis [42]. This finding highlights that, while the intercropping system can capitalize on the complementary use of land resources, the shade cast by taller crops (like jujube) still significantly influences the photosynthetic characteristics of the understory crop (cotton) [43]. This is supported by the correlation analysis results shown in Figure 8, which show that the correlation between the photosynthetic characteristics and yield in the intercropping cotton is stronger than that in the monoculture cotton. Specifically, in 2020, 2022, and 2023, the correlation coefficient between the Pn and cotton yield in the intercropping system was high, indicating that the photosynthetic efficiency was affected to a certain extent (Figure 8). In intercropping systems, shade cast by jujube trees can reduce the light availability, limit photosynthesis (source strength), and potentially lower the cotton yield [44].

Additionally, the Gs of cotton in the intercropping system was lower than that of the monoculture cotton (Figure 6). This is closely related to the insufficient light reaching the cotton plants caused by the shade cast by the jujube trees [45]. Since stomatal conductance plays a significant role in photosynthesis, Gs directly affects the photosynthetic efficiency of cotton, which, in turn, impacts its yield [46]. Despite these limitations in the photosynthetic characteristics, the overall accumulation of photosynthetic products in the jujube–cotton intercropping system was still sufficient to support a higher total yield (Table 1). This indicates that, although cotton in the intercropping system experiences light limitations and reduced photosynthetic efficiency, the resource allocation and ecological niche complementarity between the crops enable a higher overall output compared to monoculture systems [47]. Efficient carbohydrate transport from leaves to bolls is essential for cotton yield [48]. While shading in intercropping reduces light intensity, the complementary land use between jujube and cotton can improve the overall carbohydrate transport efficiency, potentially increasing the total system yield [49].

In summary, the jujube–cotton intercropping system demonstrates notable advantages in land use efficiency and economic benefits. While cotton’s photosynthetic characteristics are affected by shade cast by jujube trees, leading to a slight decrease in the cotton yield compared to that of monoculture cotton, the optimized planting patterns and resource allocation in the intercropping system increase the total yield and LER, ultimately enhancing economic returns. Moreover, the changes in photosynthesis, especially the decline in the net photosynthetic rate and the increase in the intercellular CO₂ concentration, further affect the cotton yield. This suggests that the yield changes in cotton are closely tied to the photosynthetic efficiency, highlighting the importance of optimal light and heat resource management in intercropping systems. Through scientific management and careful crop selection, jujube–cotton intercropping not only enhances cotton’s photosynthetic efficiency but also improves the overall sustainability and economic profitability of agricultural systems.

5. Conclusions

This study demonstrated a strong correlation between cotton yield and its photosynthetic characteristics, with higher net photosynthetic rates corresponding to higher yields. The findings revealed that, although both the net photosynthetic rate and yield of cotton were higher in monoculture systems than in the jujube–cotton intercropping system, the land equivalent ratio in the intercropping system exceeded 1, indicating improved land use efficiency. Moreover, the complementary effect between the jujube trees and cotton increases and stabilizes the overall economic return in the intercropping system. In conclusion, the jujube–cotton intercropping system effectively improves the land use efficiency and economic benefits, demonstrating strong sustainability and economic advantages. These findings provide valuable insights for optimizing cropping patterns and promoting the sustainable development of agricultural systems.