The experiment was conducted from June to October 2023 at the Quzhou experimental station of China Agricultural University, which is situated in the North China Plain of Hebei Province at a latitude of, 1150E, 36.50N, and an elevation of 37 m above sea level. The trial was carried out during the short growing season from 15 June to 03 October 2023. The dimensions of each plot were 8 m × 9 m in size for both monoculture and intercropped maize/soybean. Maize and soybeans were harvested after 110 days of planting. The study was conducted using a randomized block-split plot design, the main plot was divided into three cropping systems. The trial included two phosphorus treatments: one without P application (P0) and the other with a P application of 80 kg P₂O₅ per ha. Crop treatments included (1) maize alone, (2) soybean alone, and (3) soybean/maize intercropping, a maize/soybean intercrop with paired legume rows between two maize rows or two paired legume rows.

The vegetative materials used were one of the varieties of quality maize (MC812) and one variety of soybean (Jidou12). The two materials were chosen for their yield potential availability of seeds to users and breeders and also food preferences.

Plant height samples were collected at various growth stages of maize and soybeans. The samples were collected at different growth stages namely V7, V10, VT, and R1 for maize in monoculture and intercropped with maize, and also at V2, V3, R1, and R3 growth stages for monoculture soybean and intercropped soybean (Nasar et al. 2023). The growth stages of maize were classified as either vegetative (V) or reproductive (R). Three maize plants were selected randomly in each field and an average value was obtained both in monoculture and intercropped fields at different stages [28] , much focus was on V7 and V10, because these two stages are the most critical in maize, and long tape was used when measuring this height. The height was measured from the base of the plant to the tip of the tallest leaf [29] .

Chlorophyll data were collected at weekly intervals throughout the study period. Chlorophyll content was quantified using a SPAD meter, a device that measures chlorophyll levels on the leaf surface [30] . To obtain accurate readings, three random areas of each leaf were selected and measured with the SPAD meter placed on the leaf surface, and the readings were recorded. The average of the measurements was then calculated to determine the chlorophyll content for each time point [31] . Particularly important for chlorophyll content were certain growth stages during the period of data collection. These critical growth stages included V7 (7 visible leaf collars), VT (tasselling stage), V10 (10 visible leaf collars) and R1 (silking stage). Understanding the variations in chlorophyll content at these specific growth stages provides valuable insight into the physiological development of maize plants and can help optimize agricultural practices data for chlorophyll was collected every seven days. The chlorophyll content was determined using SPAD, which measures the leaf surface [32] . Three random parts of each leaf were selected and measured using the SPAD meter, the SPAD meter was placed on the leaf surface and recorded in the reading. The average value was then obtained. The actual growth stages that were much emphasized in chlorophyll during the data collection were V7, VT, V10, and R1.

Plant girth samples were methodically obtained by randomly selecting three maize plant stems within the field setting and employing a caliper tool for circumference measurement [33] . The standard protocol for measuring maize girth involved selecting the measurement point at a height ranging between 10 - 15 cm above the ground level to ensure uniformity and accuracy across samples. This meticulous approach aimed to capture the variations in stem diameter growth and development, which is indicative of the plant’s overall health and vigor [34] .

Leaf area samples were systematically collected by randomly selecting three maize leaves in the field during the pivotal growth stages of V7 and V10. A measuring tape was utilized to measure the surface area of each selected leaf, ensuring accuracy and consistency in the data collection process [35] . The measurements were taken to gain insights into the leaf development and growth dynamics of the maize plants at these critical stages. By obtaining the average leaf area value Leaf area samples were collected by randomly selecting three maize leaves in the field and measuring the area using a measuring tape during the V7 and V10 growth stages. The average value was obtained.

The statistical analysis of all the measured factors was carried out using the Analysis of variance (ANOVA) on the Statistical Package for the Social Sciences (SPSS) and sigma plot version 2020, while Microsoft Excel was utilized to organize the data in the form of tables. Origin Pro 2022b was employed for graphical representation.

Based on the data collected from the intercropped maize, there was a significant difference in the concentration of chlorophyll between monoculture and intercropping in fertilized and non-fertilized treatments at the VT stage (P < 0.05), as shown in Figure 1(a) . However, the intercropped maize with fertilized treatment had a consistently higher concentration of chlorophyll from VT to R1 as observed in the field [36] . These findings suggest that the maize crop in the non-fertilized treatment experienced delayed drying compared to the fertilized treatment.

Furthermore, the outcomes from the soybean intercropped system demonstrate that the chlorophyll concentration in the intercropped maize in non-fertilized treatment was consistently greater than in the monoculture maize non-fertilized treatment at all stages [8] , as depicted in Figure 1(b) . Moreover, the data revealed a significant increase in chlorophyll content from the VT stage in the intercropped soybean in the non-fertilized treatment compared to the monoculture maize non-fertilized treatment, as shown in Figure 1(c) . This indicates that the maize in the fertilized treatment was actively engaged in the photosynthesis process which resulted in a higher concentration of chlorophyll [31] .

The results of the intercropped soybeans revealed a higher chlorophyll concentration at the R1 growth stage in both the fertilized and non-fertilized treatments in intercropped soybeans [37] , as depicted in Figure 2(a) . Nevertheless, both treatments remained relatively low at the V3 and R3 growth stages in monoculture

soybean as illustrated in Figure 2(b) and Figure 2(c) . In comparing maize-soybean intercropping and mono-cropping systems, it was observed that the chlorophyll concentration in soybean was relatively higher in intercropped soybean than in monoculture in all the treatments [8] .

The stem diameter of intercropped maize at the V7 stage was comparable to that

of the maize monoculture at the V10 stage, where phosphorus fertilizer was not applied, as shown in Figure 3(a) and Figure 3(b) . Conversely, in Figure 3(a) and Figure 3(b) , where phosphorus fertilizer was applied, the stem diameter was higher at the V7 stage in sole maize in both treatments that are fertilized and non-fertilized, however, there was no significant difference between the stem diameters of the monoculture and the intercropping system.

The stem diameter of intercropped soybeans at the V7 and V10 growth stages, as depicted in Figure 4(a) , was nearly indistinguishable between the plots that

received phosphorus fertilizer and those that did not [11] . This suggests that there was no substantive difference between the two. The modest increase observed at V7 can be attributed to the nutrients naturally present in the soil, as well as the positive effect of the phosphorus fertilizer in promoting new cell growth and elongating existing cells, which ultimately contributes to the overall thickness and girth of the stem.

The findings demonstrated that plant growth in intercropped maize was greater at the V10 growth stage compared to the V7 growth stage in monoculture maize in all the treatments thus in fertilized and non-fertilized compared to intercropped maize [29] , as depicted in Figure 5(a) and Figure 5(b) . At the V10 growth stage, there was increased growth in both fertilized and non-fertilized treatments, as shown in Figure 5(b) . When comparing the two Figures ( Figure 5(a) and Figure 5(b) ), it is

evident that there was more growth at the V10 growth stage in both fertilized and non-fertilized treatments. However, the overall trend indicates that maize growth is more prevalent in monoculture plots than in intercropped plots [5] , as shown in both fertilized and non-fertilized treatments, as depicted in Figure 5(c) .

Figure 6 presents the grain yield of maize in both monoculture and intercrop, with and without fertilization [28] . The results indicate that the grain yield in maize monoculture was lower under non-fertilized conditions compared to the maize intercrop without fertilizer, although there was no statistically significant difference between the two [22] . Similarly, the grain yield in monoculture maize with fertilized treatment was lower than in intercropped maize, but again, there was no statistically significant difference between the two treatments (Hidoto & Markos 2021).

The results in Figure 7 showed that the sole soybean biomass was greater at the R6 growth stage in both the sole and intercropped settings, with or without fertilizer application [38] . This may be attributed to the fact that at the R6 stage,

plants are in a crucial reproductive phase where the demand for nutrients is higher to support pod development and seed filling [39] . Consequently, soybeans exhibit significant biomass production at this stage due to nitrogen fixation, irrespective of whether they are fertilized or not.

The effects of phosphorus (P) fertilization on maize/soybean intercropping systems were investigated, focusing on growth, yield, and nitrogen (N) uptake. The studies paint a complex picture. Some report that P has no significant effect on maize yield [40] . While others find an improvement in crop quality and N fixation by legumes [41] , the role of P in improving N uptake and fixation is also supported by the positive effects of farmyard manure, which likely provides P among other nutrients, on soil fertility and crop production in maize/soybean intercrops [16] . Contradictions arise when considering the effects of P fertilization on soybean yields. Some studies report higher yields in sole cropping compared to intercropping [42] , while others suggest that intercropping systems can be optimized through specific planting patterns and row ratios to improve soil productivity and nutrient uptake [43] . In addition, the interaction of P with other agronomic practices, such as injection with Latati et al. (2018) and the use of rice mill ash [18] , can significantly affect N fixation and yield. In summary, the effects of P fertilization on maize/soybean intercropping systems are diverse, with potential benefits for N uptake and fixation, plant quality, and yield. However, the effectiveness of P fertilization is influenced by several factors, including cropping patterns, soil fertility management, and the use of inoculants. Further research is needed to determine the optimal conditions under which P fertilization can maximize the benefits of maize/soybean intercropping systems.

Although there was a significant difference between the treatments, in intercropping, chlorophyll concentration was higher than in monoculture, due to the complementarity of resources, as maize and soybean have different root system structures and nutrient requirements [22] . Therefore, intercropping allows them to utilize different resources from the soil, such as nutrients and water, more efficiently than monoculture. This ensures better nutrient availability for chlorophyll synthesis, resulting in a higher chlorophyll concentration [31] . Intercropping increases biodiversity in the agroecosystem, which can promote positive interactions between plants and soil organisms [44] . This can lead to better nutrient cycling and nutrient availability, which further enhances chlorophyll production in intercropping systems, leading to higher chlorophyll concentration. Maize and soybean plants also have different canopy structures that allow for more effective light interception and utilization when intercropped. This improved light utilization can enhance photosynthesis efficiency, resulting in higher chlorophyll concentration [45] .

The grain yield of maize was lower in monoculture than in maize/soybean intercropping, which was higher. According to Hidoto and Markos 2021, efficient resource utilization Maize and soybeans have different root structures and nutrient requirements [25] . When grown in intercropping, they can use resources such as nutrients and water more efficiently. This efficient use of resources can lead to better overall plant growth and a higher grain yield than when maize is grown in monoculture. Another reason is complementarity, maize and soybean plants in a catch crop system can complement each other in terms of resource utilization [46] . For example, maize can benefit from the nitrogen-fixing capacity of soybeans, resulting in better nitrogen availability for maize growth. This complementarity can increase overall productivity and contribute to higher grain yields in the intercropping system [47] . Disease and pest control in intercropping can help reduce the incidence of pests and diseases by disrupting their host plants and habitats. This can lead to healthier maize plants with lower pest and disease pressure, ultimately contributing to higher grain yields compared to monoculture where pests and diseases may thrive more easily.

The data in Figures 5(a)-(c) illustrate the variations in plant growth across the different stages of maize cultivation, specifically in monoculture and intercropping fields [48] . The findings indicate that the plant height was greater at the V10 stage in both fertilized and non-fertilized treatments for intercropped maize in Figure 5(a) , as well as in intercropped soybean and solitary maize [49] . This growth increase is particularly noticeable at the V10 stage, which is a pivotal phase for maize development, as it lays the groundwork for ear formation and grain production [50] . At this stage, the plants have fully developed leaves, are actively growing, and are transitioning from the vegetative stage to the reproductive stage. The roots are also well-established and efficiently absorb water and nutrients. The plant is simultaneously photosynthesizing and accumulating carbohydrates for reproductive growth, and its tassel and ear start to differentiate within the plant [11] . As a result, proper management during this stage is crucial to maximize yield potential. This practice of intercropping maize and soybean has gained considerable traction worldwide, particularly in regions like China, due to its double benefits of high productivity and simultaneous harvest of two distinct grains [17] . It is important to note that the application of phosphorus to the crop resulted in increased chlorophyll accumulation and enhanced maize stem girth. The results demonstrate the effective absorption of nitrogen when phosphorus is present, resulting in accelerated growth of maize in both stages, a crucial factor contributing to increased yield [51] . These findings align with prior research indicating that maize-soybean intercropping leads to higher yields due to greater nitrogen availability [52] . Nutrients are essential for plant growth, development, and overall health, with phosphorus playing a key role in facilitating the uptake and transportation of other essential nutrients, such as nitrogen [53] . This synergistic effect promotes efficient nutrient utilization for growth and development, explaining the higher plant growth observed at the V10 stage across all treatments, regardless of fertilization. Maize plants at the V10 stage typically exhibit vigorous growth and robust root development. Adequate phosphorus levels accelerate nitrogen uptake, fostering the development of healthy root systems capable of efficient water and nutrient absorption, leading to taller plants with dark green leaves and sturdy stalks, ultimately bolstering yield potential [54] . These findings align with previous observations of growth and yield patterns in cereal and legume intercropping systems [55] . Additionally, higher chlorophyll concentrations were observed at the VT growth stage in intercropped maize, indicating increased plant growth [56] . Chlorophyll, a pigment found in plant chloroplasts, plays a crucial role in photosynthesis, the process by which plants convert light energy into chemical energy (glucose) and oxygen. This process is essential for plant growth, as glucose serves as an energy source. Regarding stem girth, while there was no significant difference between treatments, maize/soybean intercropping displayed thicker stems at the V7 growth stage [35] . The stem serves as a vital organ supporting plant growth, development, and reproduction by providing structural support, facilitating the transportation of essential substances, contributing to photosynthesis, and storing nutrients [57] .

In both treatments involving sole soybean and intercropped soybean, it is observed that there is a higher accumulation of biomass [11] . However, there is a significant difference between the two treatments. It is important to note that in mono-cropping systems, where a single crop is cultivated in a field, applying phosphorus fertilizer results in increased biomass production [58] . Phosphorus plays a crucial role in plant growth, root development, and energy transfer processes within the plant. When phosphorus availability is adequate, it enhances photosynthesis, nutrient uptake, and overall plant growth, leading to greater biomass accumulation [59] . This can be seen in Figure 7 , where a more substantial increase in biomass is observed in R3 maize mono-cropping with fertilizer content, compared to sole maize without fertilizer. The same pattern is evident in the R6 growth stage of soybean, both in sole and intercropped varieties [60] . In sole soybeans, there is a higher biomass accumulation due to reduced competition for nutrients and other resources [61] . In intercropped soybeans, competition for resources such as light, nutrients, and water is significantly higher [57] . The R6 growth stage in soybean is known as the full seed or full pod growth stage, and it is a critical phase in the development of the soybean plant. During this phase, the plant is focused on pod and seed development as it moves toward maturity [54] . At this stage, the plant reaches its maximum height and canopy development and has a well-established root system supporting pod and seed development.

Biomass in the R6 stage of both sole and intercropped soybeans demonstrated an increase in non-fertilized treatments. The R6 stage is a critical reproductive phase where the demand for nutrients is higher to support pod development and seed filling. Despite being non-fertilized, soybean biomass was higher due to its unique ability to fix atmospheric nitrogen through symbiotic relationships with rhizobia bacteria [49] . This nitrogen fixation process continues throughout the plant growth stages and provides a crucial source of nitrogen for pod development and seed filling at the R6 stage [5] . In intercropped soybeans, there was an efficient utilization of nutrients, especially during this critical phase when demand was highest, resulting in maximum biomass production without additional fertilizers [62] . This nutrient remobilization helps sustain high biomass production. The presence of other crops in the intercropped soybean creates a more diverse and dynamic growing environment, which enhances nutrient cycling, improves soil health, and promotes overall plant growth [5] . This contributes to high biomass production in soybeans at the R6 stage.

The outcomes of grain yield for single and intercropped maize in Figure 6 for fertilized and non-fertilized treatments indicate that in sole maize, the grain yield was low [39] . This may be due to competition among the plants for resources such as sunlight, water, and nutrients [63] . This competition can limit the growth and yield potential of individual plants, leading to decreased overall productivity. In contrast, intercropped maize had relatively higher yields [64] . This may be because maize is a heavy feeder crop that requires significant amounts of nutrients for optimal growth and yield [65] . Non-fertilized treatments in sole maize experienced nutrient deficiencies, which restricted its growth and reduced its yield potential. Intercropped maize, on the other hand, benefited from nutrient cycling and enhanced nutrient availability through interactions with the companion crop, resulting in higher yields [35] . Additionally, cereal-legume intercropping can improve diversification in nutrient uptake by the component crops, increase environmental resource use efficiencies, and result in higher yields per unit area compared to sole cropping [66] .