The effects of maize varietal traits and maize planting density on soybean-maize relay strip intercropping

Yang, Y., Long, Y., Zhang, T., Tang, M., Wang, Y., Cheng, M., Li, C., and He, C. (2026). "The effects of maize varietal traits and maize planting density on soybean-maize relay strip intercropping," BioResources 21(4), 10309–10325.

Abstract

As a major consumer of soybean, the growth in China’s annual soybean production is crucial to its national food security. Both maize and soybean are upland crops with overlapping growth periods, leading to trade-offs in production when either crop is cultivated as a sole crop. However, the soybean-maize strip intercropping system enables the production of an additional soybean harvest with only a slight reduction or no loss in maize yield, thereby making a highly significant contribution to the expansion of total grain output. This study explored the effects of maize varietal traits and maize density on the production indicators of the two crops under this intercropping model by designing different maize varieties and maize planting densities. The results showed that maize lodging extent had an extremely significant negative correlation with maize yield and gross income. Maize plant height had a significant negative correlation with maize 100-grain weight, soybean SPAD values, and soybean grains per plant. Within a certain range, as maize density increased, maize yield first increased and then decreased, while soybean yield showed a continuous downward trend. Based on this regularity, a quadratic function mathematical model was constructed, with maize planting density as the independent variable and production benefit per unit area as the dependent variable. This model can be used to determine the optimal maize planting density for soybean-maize relay strip intercropping. This study identifies suitable maize varieties and optimal planting density, thereby providing references for local production practices.

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The Effects of Maize Varietal Traits and Maize Planting Density on Soybean-Maize Relay Strip Intercropping

Yun Yang,^a Yun Long,^b,* Ting Zhang,^a Mingshuang Tang,^a Ying Wang,^a

Mingming Cheng,^a Chunyan Li,^a and Chuan He ^a,*

DOI: 10.15376/biores.21.4.10309-10325

Keywords: Maize varietal traits; Maize planting density; Correlation; Production benefit; Mathematical model

Contact information: a: Nanchong Academy of Agricultural Sciences, Nanchong 637000, China; b: College of Life Science, China West Normal University, Nanchong 637002, China;

* Corresponding author: [email protected]; [email protected]

INTRODUCTION

Soybean and maize are both major food and forage crops in China. In 2022, soybean accounted for 10.04% of China’s total grain output, while maize accounted for 36.40% (National Bureau of Statistics 2023). Additionally, as both soybean and maize are upland crops with overlapping growth periods, this leads to tight land resource utilization and a large supply-demand gap. Currently, China’s annual soybean imports have long remained above 80 million tons, and maize imports above 20 million tons. According to predictions, by 2029, China will still need to import 99.52 million tons of soybean and 6.48 million tons of maize (Expert Committee of Market Early Warning 2020). Scientific and rational land use, alleviating land use conflicts, and increasing soybean and maize yields are crucial issues to be addressed at present, as well as important measures for the reform of China’s agricultural cropping systems.

Intercropping and relay cropping of crops can improve land use efficiency. As a long-standing cultivation pattern in China, it can be traced back over 2,000 years ago, such as the mixed planting of melons with Chinese chives, or adzuki beans, mulberries with broomcorn millet (Li 1995; Dong and Shen 2000). In the 1990s, the wheat-maize-sweet potato Intercropping and relay cropping pattern gradually took shape in the hilly and mountainous areas of southwest China. However, both wheat and sweet potato are dense-planted crops, occupying a large area with limited space savings. Compared with maize-based intercropping/relay cropping, this pattern showed insignificant effects and was prone to causing soil erosion. Around 2000, Yang Wenyu’s research team launched studies on the new triple-cropping intercropping/relay cropping pattern of “wheat-maize-soybean” (Liu and Wan 2022). This cropping system optimizes population configuration based on the principle that canopy structures of different heights (tall and short crops) have different light utilization efficiencies. It regulates the light environment for soybean-maize intercropping/relay cropping. It achieves the symbiosis of maize and soybean by utilizing the nitrogen-fixing effect of soybean and the edge effect of maize. In fields where only maize was previously planted, the soybean-maize strip intercropping cropping system realizes the goal of “no reduction in maize yield while gaining an additional soybean harvest”. Currently, this cropping system has been included in China’s Central Document No. 1 for three consecutive years.

This cropping system has been investigated with different row ratio configurations and crop row orientations of soybean and maize. Under the configuration of 2 rows of maize and 4 rows of soybeans, the light transmittance in the middle and lower parts of maize was the highest, along with the maximum net photosynthetic rate and dry matter accumulation (Wu et al. 2023). In southern China, relay strip intercropping with an east-west row orientation achieved the highest maize yield contribution rate, enabling the maximum advantages of relay strip intercropping (Ning et al. 2023). For variety selection in strip intercropping, compact maize varieties should be prioritized (Cui et al. 2015), and shade-tolerant soybean varieties are more suitable (Ma 2020). Studies on the effect of soybean nitrogen-fixing function on maize growth revealed that soybean-maize intercropping/relay cropping could better enhance the aboveground biomass production capacity of maize and improve the underground root distribution environment (Xiao et al. 2022). An appropriate interspecific spacing (60 cm between maize and soybean rows) could increase the number and fresh weight of soybean nodules, thereby enhancing the nitrogen-fixing potential of soybean nodules (Liu et al. 2023). In studies on maize planting density in the soybean-maize intercropping/relay cropping system, Chen (2023) concluded through experiments that a maize planting density of 48,000 plants/ha in southern China is conducive to increasing the total yield and total output value of the soybean-maize intercropping/relay cropping population (Chen 2023).

Our research group has previously conducted multiple studies on maize variety selection and identification as well as density selection in soybean-maize relay strip intercropping (Yang et al. 2025; Jin et al. 2020). The results showed that different maize varieties under the soybean-maize relay strip intercropping pattern not only affect maize yield but also soybean yield. Furthermore, maize planting density, maize yield, and soybean yield are all continuous quantitative traits. By conducting in-depth analysis of each quantitative trait to explore their inherent linear relationships, we aim to predict field production benefits.

EXPERIMENTAL

Experimental Site and Materials

The experiment was conducted in Luxi Town, Shunqing District, Nanchong City, China (106°8′28″ E, 30°57′26″ N). The area features hilly terrain and a subtropical humid monsoon climate, with an annual average temperature of 17 ℃ and an annual rainfall of 800 to 900 mm. This field has long been used for the rotation of monocropped spring maize and monocropped spring soybean, and it is classified as basic fertile farmland with medium loam soil and moderate fertility.

For the experiment on maize trait research, 10 new maize varieties with high yield, abiotic stress resistance, high-density tolerant, lodging resistance, and moderate growth period were selected, including Nanyu 88 (M1), Zhongdan 901 (M2), Kangnongyu 108 (M3), Kemao 918 (M4), Haodan 568 (M5), Chengdan 30 (M6), Zhongyu 3 (M7), Miandan 53 (M8), Zhongyu 335 (M9), and Nanyu 21 (M10). The soybean variety used in this experiment was Nanxiadou 25; this variety exhibits high yield, drought resistance, and shade tolerance.

For the experiment on density research, the maize variety Zhongyu 3 was selected. This variety has a compact plant type, short plant height, and strong stress resistance, making it suitable for intercropping with soybean. Soybeans planted between rows of this maize variety can receive more sunlight. The soybean variety used here was Nanxiadou 25, a variety with high yield, shade tolerance, and disease resistance.

Experimental Design

The experiment was conducted over two consecutive years (2022–2023), adopting the pattern of 2 rows of maize intercropping-cropped with 3 rows of soybeans. Maize was sown from late March to early April and harvested in early August, while soybeans were sown in mid-June and harvested from mid-to-late October of the same year. Two separate experiments were conducted: the maize trait experiment and the maize density experiment.

For the maize trait experiment, ten local elite maize varieties were used. A randomized complete block design with three replications was adopted, and treatments were randomly arranged within each block. The planting density was set at 52,579 plants/ha for maize and 112,618 plants/ha for soybeans. The width of each soybean-maize strip was 2.4 m, with a spacing of 40 cm between maize rows, 70 cm between maize and soybean rows, and 30 cm between soybean rows. The hill spacing in the corn rows was 31.7 cm, and the hill spacing in the soybean rows was 22.2 cm. Both crops were sown with 2 plants per hill, and each plot had a row length of 9 m. A production unit was defined as 2 rows of maize plus 3 rows of soybeans; three such production units constituted one plot (total area: 64.8 m²), and the experiment was replicated three times. Of the three production units, the two on either side served as buffer zones for edge effects. Data for maize and soybean were collected exclusively from the middle production unit of each plot for subsequent analysis.

For the maize density experiment, Zhongyu 3 was selected as the maize variety. Five maize planting densities were designed: 30,000, 37,500, 45,000, 52,500, and 60,000 plants/ha. The soybean density was uniformly fixed at 112,500 plants/ha. In this experiment, only the hill spacing was adjusted. The five density levels from low to high correspond to corn hill spacings of 55.56 cm, 44.44 cm, 37.04 cm, 31.74 cm, and 27.78 cm respectively, while the soybean hill spacing was fixed at 22.22 cm. All other experimental settings were consistent with those of the maize trait experiment.

Determination Indicators

For the maize trait experiment, the following data were recorded: intermediate production unit maize plant type, maize lodging extent (ML), maize plant height (MH), maize 100-kernel weight (MW), maize grains per ear (MG), maize yield (MY), soybean lodging extent (SL), soybean SPAD value (SV), soybean 100-grains weight (SW), soybean grains per plant (SG), soybean yield (SY), and gross income (GI).

For the maize density experiment, the following data were recorded: intermediate production unit maize planting density (MD), maize whole growth period (MGP), maize hollow-stalk extent (MV), maize lodging extent (ML), maize yield (MY), soybean whole growth period (SGP), soybean grains per plant (SG), SPAD value of soybean upper leaf (SV), and soybean yield (SY).

During data collection, MW and SW were measured in only 3 replications. For MH / MG / SV / SG, only the middle 20 consecutive crop plants were recorded, while for ML / MY / SL / SY / GI / MGP / MV / SGP, all corresponding plants in the plot were recorded. MGP and SGP refer to the number of days recorded until half of the maize or soybean plants in the quadrat reach maturity. Maize maturity is defined as the appearance of a black layer at the base of the kernels, while soybean maturity is indicated by fully yellowed or browned pods.

For soybean, the SPAD value was determined by averaging the upper and lower 5 leaves near the pods. The chlorophyll meter used was Model JC-YLS-Ⅱ, manufactured by Qingdao JCJH Analytical Instrument Co., Ltd., Qingdao, China. Lodging extent was defined as plants leaning at an angle of less than 45°relative to the ground or with broken stems. For maize varieties, plants with the middle and upper leaves growing upward close to the stalk at an angle of within 30°were classified as compact type; those with an angle of 30°to 45°as semi-compact type; and those with an angle of more than 45°as flat type.

ML and SL represent maize lodging extent and soybean lodging extent, respectively, calculated as the number of lodged maize/soybean plants in the quadrat divided by the total number of corresponding crop plants in the quadrat.

MV refers to the hollow-stalk extent, calculated as the number of maize plants with fewer than 20 grains per ear in the quadrat divided by the total number of maize plants in the quadrat.

GI represents the total gross income of crops in the quadrat, computed by the formula,

GI = a·x + b·y (1)

where a and b are derived from the average purchase prices of maize and soybean in China during 2022–2023, with a = 2.59 CNY/kg and b = 5.40 CNY/kg; x is the converted maize yield per hectare, and y is the converted soybean yield per hectare.

Statistical Analysis

All data were processed for standardization of data types and data normalization using Microsoft Excel 2007, which was also used for linear regression analysis and graphing. Origin 2021 was employed for correlation analysis and graphing, while SPSSPRO was utilized for significance analysis and multiple comparison.

RESULTS

Agronomic Trait Performance of Maize and Soybean Under Intercropping with Different Maize Varieties

As shown in Table 1, there were significant differences in traits among different maize varieties. The 100-kernel weights of both maize and soybean showed significant differences between years, while the interaction between year and variety was not significant. In the maize trait experiment, most of the 10 maize varieties had a semi-compact plant type. The highest lodging extent of maize reached 41.3%, whereas the lowest was 0% (variety M7). The plant height of maize ranged from 239 cm to 315 cm. The 100-kernel weight of maize grains was relatively consistent, ranging mainly from 30.1 g to 32.0 g, with the lowest value of 27.8 g observed in M4. The number of grains per maize ear showed no significant difference, ranging from 492 to 572 grains per ear. Maize yield ranged from 6140 kg/ha to 7940 kg/ha. No obvious lodging was observed for soybeans between rows, with a lodging extent of 0% in most treatments.

Fig. 1. Field yields of maize and soybean under intercropping with different maize varieties. (Data are presented with three significant figures. Maize variety, M1: Nanyu 88, M2: Zhongdan 901, M3: Kangnongyu 108, M4: Kemao 918, M5: Haodan 568, M6: Chengdan 30, M7: Zhongyu 3, M8: Miandan 53, M9: Zhongyu 335, M10: Nanyu 21; agronomic Trait, MY: maize yield, SY: soybean yield.)

Table 1. Agronomic Trait Performance of Maize and Soybean Under Intercropping with Different Maize Varieties

(P<0.05) and extremely significant (P<0.01) effects, respectively. Data are presented with three significant figures. Maize variety, M1: Nanyu 88, M2: .

The highest SPAD value (SV) of soybean leaves was 47.7 (recorded in M2). The 100-kernel weight of soybean showed no significant difference, but the number of grains per soybean plant varied greatly—ranging from a maximum of 114 grains per plant to a minimum of 71.08 grains per plant. The converted soybean yield mainly ranged from 701 kg/ha to 1100 kg/ha.

The results showed that the highest total field income of 26,200 CNY/ha was achieved when maize variety Miandan 53 was planted. Maize and soybean yields are key components of field income, and Fig. 1 illustrates the yields of maize and soybean. Under intercropping, the highest maize yield of 7940 kg/ha was achieved when variety M8 was used. This was followed by M5, M7, and M6, which also showed good performance in maize yield, reaching 7780, 7490, and 6810 kg/ha, respectively. When maize varieties M7, M4, M1, and M8 were intercropped, the soybean yields were relatively high, reaching 1100, 1070, 1050, and 1050 kg/ha, respectively.

Correlation Analysis of Maize and Soybean Agronomic Traits Under Intercropping with Different Maize Varieties

After intercropping soybeans with different maize varieties, correlation analysis was performed on the field data of agronomic traits of maize and soybean. As shown in Fig. 2, maize lodging extent had a very significant negative correlation with maize yield and total income.

Fig. 2. Correlation analysis of maize and soybean agronomic traits under intercropping patterns with different maize varieties

Maize plant height exhibited a significant negative correlation with maize grain 100-kernel weight, soybean SPAD values, and soybean grains per plant. Maize 100-kernel weight showed a significant negative correlation with soybean lodging extent. In contrast, maize yield, soybean yield, and total income all had extremely significant positive correlations with each other. Soybean lodging extent had an extremely significant negative correlation with soybean SPAD values; meanwhile, soybean SPAD values had an extremely significant positive correlation with soybean grains per plant, and soybean grains per plant also had an extremely significant positive correlation with soybean yield.

Thus, a high maize lodging extent will lead to a reduction in maize yield and directly decrease the total field income. Additionally, a taller maize plant height will result in a lower maize 100-kernel weight, reduced soybean photosynthesis, and fewer soybean grains per plant.

The Influence of Corn Density in the Intercropping System on Crop Agronomic Traits

Results of field trait investigation and yield measurement are presented in Table 2. Different years had an extremely significant effect on the growth periods of maize and soybean, and a significant effect on maize yield. Different treatments had an extremely significant effect on all traits of maize and soybean. In contrast, the interaction between year and treatment had no significant effect on any trait of maize or soybean.

Analysis and comparison of data from 2022, 2023, and the two-year average showed that at a maize density of 30,000 plants/ha, maize had the longest full growth period, and the lowest hollow-stalk rate and lodging extent; meanwhile, soybean had the longest full growth period, the highest effective pod number, the largest SPAD value, and the highest yield.

All of these traits (for both crops) showed extremely significant differences compared with those at a maize density of 60,000 plants/ha. Maize yield reached its maximum value of 7230 kg/ha at a maize density of 45,000 plants/ha.

Correlation Analysis between Maize Planting Density and Crop Traits under the Intercropping System

Pearson correlation analysis was performed based on the recorded data of each trait, and the results are shown in Fig. 3. Except that maize yield only had a significant negative correlation with soybean yield, all other traits exhibited extremely significant positive or negative correlations to varying degrees.

Among these, maize planting density in this experiment was the independent variable causing changes in other traits, while the remaining traits were dependent variables. Thus, we focused on observing the relationship between maize planting density and each trait, and found the following: maize planting density had an extremely significant negative correlation with maize whole growth period, soybean whole growth period, soybean grains per plant, SPAD value of Soybean upper leaf, and soybean yield; it had an extremely significant positive correlation with maize hollow-stalk rate and maize lodging extent; and it had no correlation with maize yield.

Table 2. Effects of Different Maize Planting Densities on Maize and Soybean Characters under Maize Intercropping Mode

Fig. 3. Correlation analysis of maize planting density and crop traits under the intercropping system

Establishment of Linear Regression Equations for Maize and Soybean Yields

Scatter plots were plotted with maize planting density (x) as the abscissa and data of maize yield (y_M) and soybean yield (y_S) as the ordinates, respectively. Then, trend lines were added to the obtained scatter plots, and univariate quadratic equations for maize yield and soybean yield under different maize planting densities were derived:

For maize yield: y_M = -6×10⁻⁶x² + 0.5911x – 6463.7 (R² = 0.7871) (2)

For soybean yield: y_S = 6×10⁻⁷x² – 0.0754x + 2921.6 (R² = 0.8597) (3)

The coefficient of determination (R²) of the constructed regression equations was greater than 0.75, indicating a high degree of agreement between the data and the fitted functions. This means that when maize density (x) is in the range of 30,000 to 60,000 plants/ha, these functions can be used for predicting the yield of the corresponding crop. As shown in the plots, within the range of 30,000 to 60,000 plants/ha for maize density (x), maize yield showed a trend of first increasing and then decreasing, while soybean yield showed a decreasing trend that was steep initially and then gentle.

Fig. 4. Yield trend of soybean and corn. Planting density is on the X-axis, and corn/soybean yield is on the Y-axis.

Establishment of Mathematical Model for Production Benefit

The function model for the production benefit (y) of maize intercropped with soybean per unit area was obtained by multiplying the aforementioned mathematical models for unit yield of maize and soybean by the unit price of maize (a) and soybean (b), respectively, and then summing the results. The model is expressed as follows:

y = (6b×10⁻⁷ – 6a×10⁻⁶)x² + (0.5911a – 0.0754b)x + 2921.6b – 6463.7a

This function represents a downward-opening parabola. Solving the equation gives the maize planting density (x) at which the intercropping production benefit (y) reaches its maximum:

x = (75400b – 591100a)/(1.2b – 12a)

The corresponding maximum production benefit is:

y = (552.78b² + 1461.08ab – 80946a²)/(b – 10a)

With reference to the local average prices in Southwest China in recent years (maize: a = 2.59 CNY/kg; soybean: b = 5.4 CNY/kg), the optimal sowing density of maize was calculated to be 45,700 plants/ha, and the corresponding production benefit was 24,700 CNY/ha.

DISCUSSION

The Effects of Maize Plant Height and Lodging Extent on the Benefit of the intercropping System

Maize-soybean strip intercropping system was proposed based on the theory and practice of soybean biological nitrogen fixation and stratified light utilization by maize and soybean. Under this model, the synergistic effect between soybean and maize is remarkable. Legumes have been recognized as the crop with the highest contribution of biological nitrogen fixation (BNF) among grain crops, with reported BNF values reaching up to 450 kg N /ha (Hungria and Mendes 2015). In addition, part of the nitrogen fixed by soybean is released into the soil via root exudation, nodule abscission, and other pathways, becoming available nitrogen for uptake by other plants, which provides a nitrogen source for maize growth in intercropping systems (Nakei et al. 2022). Furthermore, the shallow root system of soybean and deep root system of maize form a vertical distribution in the soil, alleviating competition for phosphorus, potassium and other trace elements in the soil, which also facilitates the practical application of this cropping model (Gao et al. 2010). In terms of stratified light utilization, soybean is sown in mid-June under the relay intercropping mode. By late July, soybean remains at the seedling stage with mainly vegetative growth and no reproductive growth, requiring limited light; the light intensity between maize rows is basically sufficient for its normal development. When soybean demands more light in August, maize has already been harvested and its straws cut down, ensuring adequate light for soybean to enter reproductive growth normally. The appropriate temporal matching between the two crops is also a major scientific basis for the proposal of this model. Finally, studies have shown that in maize-soybean intercropping, tall maize plants act as a spatial barrier to a certain extent, impeding the spread of soybean diseases and insect pests among different production units (Okigbo and Greenland 1976).

During intercropping, soybean and maize exhibit both mutualistic symbiotic and competitive relationships (Cheng et al. 2023). In terms of mutualism, the nitrogen fixation by soybean roots cannot fully meet soybean’s own nitrogen demand in agricultural production, requiring supplementary nitrogen fertilizer application, and the nitrogen supply to maize is even less (Ciampitti and Salvagiotti 2018). Meanwhile, soybean and maize compete for macroelements and microelements under this cropping pattern (Aerts 1999; Lv et al. 2014). Even maize with shorter plant height can block most of the sunlight between rows, causing shading on soybeans (Liu et al. 2017; Fan et al. 2018). Similarly, during intercropping, lodged maize plants can crush the soybeans between rows; both factors directly lead to soybean yield reduction. This conclusion is largely consistent with the findings of this study. In this study, both maize lodging extent and maize plant height showed a negative correlation with soybean yield, among which maize plant height had a significant negative correlation with the number of grains per soybean plant.

In the maize trait experiment of this study, the correlation coefficient between maize yield and soybean yield was only 0.13, indicating no significant correlation. This implies that under suitable conditions, there is a possibility that both maize and soybean yields can reach high levels, which warrants further exploration in subsequent studies. Additionally, excluding the direct impact of maize yield and soybean yield on the total income per unit area, maize lodging extent had an extremely significant negative correlation with maize yield, total income. This indicates that maize lodging is a direct cause of maize yield reduction, which in turn leads to a decrease in total income. This finding has been confirmed by previous studies (Xue et al. 2017).

Maize plant height had a significant negative correlation with soybean SPAD values, indicating that taller plant height indeed exerts a negative impact on the photosynthesis of soybean leaves and reduces the number of pods formed. In the study conclusions, soybean SPAD values were inversely proportional to soybean lodging extent and directly proportional to the number of pods per soybean plant. This suggests that weak photosynthetic capacity of leaves will lead to soybean lodging and a reduction in pod number, which is consistent with the conclusion that insufficient photosynthesis causes excessive elongation of plants and thin stems, thereby increasing susceptibility to lodging (Vince 1964; Wang et al. 2023). Ultimately, this will directly affect soybean yield and the total crop income of the field.

The Effect of Maize Planting Density on Two Crops Under the soybean-maize intercropping System

Crop planting density has a direct impact on leaf photosynthesis and root nutrient uptake (Prasad and Brook 2005; Ren et al. 2016; Peng et al. 2019). A high planting density increases the leaf base number per unit area. Since solar energy per unit area is basically fixed in a certain period, exceeding a certain planting density threshold will reduce the light received by each leaf. Consequently, the organic matter fixed by a single plant through photosynthesis decreases simultaneously, leading to a reduction in the yield of individual crops (Wu et al. 2019).

Similarly, the total soil mineral elements per unit area are basically fixed in a certain period. When planting density increases beyond a certain threshold, the mineral elements available to a single plant also decrease. This manifests in crops as nutrient deficiency and malnutrition, which eventually block certain metabolic pathways and reduce crop yield (Zewide et al. 2023).

This theory is consistent with the results of this study. With the increase in maize planting density, the impacts on both maize and soybean are direct and significant: maize whole growth period decreases, while maize hollow-stalk rate and lodging extent increase; the growth environment of soybeans is suppressed, as reflected by the decreases in soybean whole growth period, soybean grains per plant, SPAD value of soybean upper leaves, and soybean yield (Akunda 2001). However, due to the increased number of maize plants, the change in maize yield is not significant.

Exploration of the Optimal Cultivation Pattern Under Soybean-Maize Relay Strip Intercropping

The fundamental goal of soybean-maize strip intercropping is to achieve higher income per unit area from crop cultivation (Iqbal et al. 2019). Maize yield and soybean yield are two key components of this income; however, the two crops exhibit competitive relationships during growth, competing for both sunlight and soil nutrients. Nevertheless, conflicts in this competitive mechanism can be alleviated—for example, by intercropping maize varieties with low-fertility tolerance, short stature, and lodging resistance with shade-tolerant soybeans at an appropriate density (Martin et al. 1998; Li et al. 2022).

In this combination: nutrient-poor-tolerant maize can maintain normal growth without being significantly affected by insufficient soil nutrients; short-statured maize allows more sunlight in inter-row spaces to be available for soybean growth (Fortin et al. 1994). This conclusion is consistent with the findings of this study that maize plant height is inversely proportional to soybean SPAD values and soybean grains per plant; the lodging resistance trait prevents maize from lodging under high-density conditions, which would otherwise affect subsequent nutrient accumulation in maize and crush inter-row soybeans (thus reducing soybean yield)—this aligns with the study’s conclusion that maize lodging is inversely proportional to maize yield.

Planting density, in addition to variety selection, is a critical cultivation factor. This study found that under the relay strip intercropping pattern, as maize planting density increased, maize yield first increased and then decreased, while soybean yield decreased rapidly initially and then slowly. The reason for this is straightforward: within a certain area, when sunlight and soil nutrients are sufficient, increasing the number of maize plants leads to higher yield. After reaching a threshold, however, further increasing maize density intensifies competition for sunlight and soil nutrients, inhibiting the growth of individual maize plants (Sherefu and Zewide 2021). The more maize plants per unit area, the lower the yield per plant, ultimately resulting in a decline in total maize yield per unit area. For soybeans in intercropping, they are constantly under competitive pressure from maize: when maize density initially increases, a higher proportion of sunlight is blocked, leading to a significant reduction in soybean yield; in the later stage, as the number of maize plants per unit area continues to increase, increased leaf overlap among maize plants reduces the blocking of sunlight gaps, mitigating the impact on soybeans and slowing the rate of soybean yield reduction (Prasad and Brook 2005).

By analyzing the underlying mathematical patterns, this study established a mathematical model for production benefit using the annual average grain prices of maize and soybean (as constants) and maize planting density (as a variable). This model preliminarily explores the production income per unit area under soybean-maize relay strip intercropping, aiming to provide theoretical support and practical reference for cultivation design in field production.

CONCLUSIONS

Maize variety selection exerts a certain impact on the soybean-maize relay strip intercropping system. Cultivating maize varieties with low lodging extent and short plant height facilitates an increase in the total field income of this system.
Under the soybean-maize relay strip intercropping system, with the increase in maize planting density, maize yield first increases and then decreases, while soybean yield first decreases rapidly and then slowly.
Based on the relationships between maize density, maize yield, and soybean yield in the soybean-maize relay strip intercropping system, a mathematical model for production benefit per unit area was established, aiming to provide theoretical references for agricultural production under this system.

ACKNOWLEDGMENTS

The authors thank Dr. Long Yun for her guidance and assistance in this study, Zhang Ting for organizing the data of this paper, and the other authors of this paper for their work in data collection. This paper would not have been published without their hard work.

FUNDING STATEMENT

This research was funded by Research on Occurrence Regularity and Green Prevention‑control Technology of Melanagromyza sojae in Nanchong City (Nanchong Science and Technology Bureau Project), No. 22JCYJPT0022.

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Article submitted: October 27, 2025; Peer review completed: March 21, 2026; Revised version received: March 27, 2026; Accepted: August 24, 2026; Published: September 3, 2026.

DOI: 10.15376/biores.21.4.10309-10325