Effect of intercropping mungbean on maize and sunflower under weed-free and weedy conditions

1. Introduction

Farming is our primary industry, employing 18% of the population and contributing 9% to the GDP. The value added from the agriculture sector is 24%, but this category accounts for 0% of the total economic sector. The actual expenditure for this sector depends on the country’s financial capability, which is about 5% of the GDP (Aslam et al., 2017). Corn production declined during the 2017-2018 season, dropping to 7%. In the previous season (2015-2016), 70% of the corn produced was utilized by restaurants, which consumed up to 13 tons of corn (Ibrahim Abdel-Wahab, 2016). The decrease in maize crops is attributed to a shift towards higher-yielding crops such as rice and sugar. Maize is the third major cereal crop in Pakistan, following rice and wheat, and holds significant production potential. However, this potential remains unfulfilled due to lower yields attributed to various biological and environmental factors (Anas et al., 2017). Intercropping offers numerous advantages over monoculture, as it typically results in higher absolute yields and reduces risk for producers (Saudy et al., 2015). This farming method could enhance productivity on small-scale farms in Pakistan. However, the traditional spatial distribution of crops hinders the development of effective agricultural practices (Shafi et al., 2007). While intercropping could be beneficial for small and medium-scale agricultural practices in developing countries, it is not widely adopted in Pakistan for various reasons, which will be explored later in this paper. The recurrent grain growth has led to soil nutrient depletion and reduced plant vigor, resulting in an imbalance in nutrition and an increased presence of wheat-related herb banks (Begna et al., 2011) (Fig. 1).

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Fig. 1.

Illustration of benefits and outcomes of intercropping maize and sunflower with legume crops, indicating enhanced productivity, improved nutrition, pest and disease control, moisture and soil conservation.

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Intercropping can effectively address numerous agricultural challenges with few restrictions on crop combinations. Mungbean (Vigna radiata L.) can be cultivated as green manure, hay, or a cover crop, and can also be intercropped with cereals, sunflower, sugarcane, or jute (Mithila, 2013). Following drought, mungbean ranks second in yield among pulses, only behind soybean (Li et al., 2017). Mungbean is an important crop in low to mid-altitudinal zones of tropical regions, primarily grown as a rainfed crop (Temesgen et al., 2015). These components indicate that plants play a critical role in supporting more resilient agricultural systems. Low-density grass serves as food storage and provides shade for beneficial plants (Dahmardeh & Hodiani, 2016). As noted by Pandey and Mishra (2003), competition from grasses resulted in a 45.6% reduction in green bean productivity. Green beans are inherently less competitive with weeds, making weed management essential for successful cultivation. The highest average seed yield of green beans, at 2108 kg/ha, was achieved in weed-free conditions (Shekhawat et al., 2017), while Malik et al. (2005) observed a 69% reduction in grain yield due to weed competition. Weeds pose significant challenges for space, nutrients, water, and light, leading to lower yields. Competition begins early in the crop’s growth and continues until maturity (Farooq et al., 2011; Eure et al., 2015). Issues arise for green beans when weeds emerge during critical growth phases such as flowering or pod development. Weeds can alter the shape of the pods, diminishing overall yield. When weed populations reach critical levels, they can severely impact both yield quantity and quality. While intercropping may enhance performance, it does come with challenges, including the need for increased expertise and advanced tools, as noted by Yilmaz et al (2008). Additionally, certain pests and diseases can easily transfer residues to neighboring crops. The combination of sunflower and maize intercropped with legume is chosen because both crops complement each other in growth and resource utilization. Mungbean is a short crop with fixes nitrogen, while the other two crops are tall and require nutrients for their proper growth. The mungbean covers the crop, hence there is a smaller number of weeds. This combination helps provide better sunlight, water, and other required nutrients and enhances productivity, particularly in feed feed-free environment (Liang et al., 2020; Khan and Akmal, 2021).

Given these considerations, an experiment was planned to determine the most suitable crop for intercropping with maize to improve yield (Weerarathne et al., 2017; Koyejo et al., 2023). The present study aims to compare the productivity of intercropping systems in weed-free and weed-infested environments against monocropping systems, while also assessing their bio-economic value. It was hypothesized that Intercropping mungbean with maize and sunflower under weed-free conditions significantly improves growth, yield, and economic returns compared to sole cropping and weedy conditions.

2. Materials and Methods

The study was conducted in the research section of the Department of Agronomy, Faculty of Agricultural Science and Technology (FAST), Bahauddin Zakariya University, Multan, Pakistan, over the years 2018-2019. The experimental site is situated at a geographic coordinate of 30°25’75”N and 71°51’55”E. This study aimed to investigate the effects of legume intercropping on maize and sunflowers under both weed-check and weed-free environments. The varieties Sunflower (NK-SINGI), Maize (P-1439), and Mungbean (HAZARI-2006) were sown on 20^th January. The following steps were adopted in this experiment. randomized complete block design (RCBD) was utilized to design the experimental units, which included split preparation and three replications. Each experimental unit covered an area of 15 m². The Agroclimatic data about (mean temperature, precipitation, relative moisture (%), and sunshine) for the year 2018-2019 were obtained from the Central Cotton Research Institute (CCRI) in Multan, as displayed in Fig. 2. Sowing was done through drilling by maintaining a space between R×R as 75 cm, and P×P as 25 cm.

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Fig. 2.

Illustration of Mean temperature, mean moisture (%), mean precipitation (mm), and mean sunshine (hrs.) during the crop year 2018-19 collected from CCRI, Multan

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Observations and data were recorded from 35 days after sowing (DAS) until harvest. Data on various allometric, agronomic, and yield traits were collected for the following parameters: plant height (cm), cob/head diameter (cm), weight of 1000 grains, biological yield, and harvest index. Weed diversity was assessed by measuring individual weed density, total weed density (m²), broadleaf weed density (m²), and grassy-leaf weed density at different DAS (35, 55, 75, and 95). Additionally, observations for parameters such as the number of roots, root length, chlorophyll content, and leaf area index (LAI) were recorded at various DAS. Chlorophyll content is estimated by placing a leaf in the soil plant analysis development (SPAD) meter, which measures light absorption at two wavelengths. The device calculates a SPAD value, indicating relative chlorophyll concentration without damaging the leaf.

3. Results

The results revealed that intercropping mung bean under weed check and weed-free environments significantly affects maize for all the traits, including plant height, cob diameters, cob length, number of grains, grain yield, biological yield, 1000-grain weight, and harvest index. The results were also significant for all the parameters of sunflowers, including plant height, cob diameters, grain yield, biological yield, 1000-grain weight, and harvest index. The data was summarized at a 5% level of significance, indicated in Table 1.

3.3 Parameters checked at different DAS (35, 55, 75, 95) under intercropping maize and sunflower in mungbean weed-free and weed-check conditions

Data on various parameters contributing to yield were collected at four different plant growth stages (35, 55, 75, and 95 DAS). The results have been presented in Fig. 3(a-h). The periodic graph shows that the number of roots, root length, chlorophyll content, and LAI of sunflowers consistently increase from 35 days to 95 days (Fig. 3a, c, e, g). Under sole sunflower weed-free conditions, there is a maximum number of roots and root length. In contrast, intercropping sunflower with mung bean in weedy conditions results in a minimum number of roots and root length. Sole sunflower in weed-free conditions also produces the highest chlorophyll content compared to other treatments, while the sunflower and mung bean intercropping in weedy conditions yields the least. The periodic data indicate that root length, number of roots, chlorophyll content, and leaf area in maize gradually increase from 35 to 95 days (Fig. 3b, d, f, h). The graph demonstrates that sole maize under weed-free conditions exhibits the maximum number of roots and root length compared to other treatments, whereas intercropping maize with mung bean in weedy conditions results in the minimum. Additionally, sole maize under weed-free conditions produces the highest chlorophyll content and leaf area index, while intercropping maize with mung bean in weedy conditions yields the least.

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Fig. 3.

Data for different traits at different DAS (35, 55, 75, 95) for Maize and Sunflower intercropping (a) Root length of Sunflower and Sunflower + Mungbean at different (DAS) in weed-check and weed-free environments (b) Root length of Sole Maize and Maize + Mungbean at different (DAS) in weed-check and weed-free environments (c) Number of roots of Sunflower and Sunflower + Mungbean at different (DAS) in weed-check and weed-free environments (d) Number of roots of Sole Maize and Maize + Mungbean at different (DAS) in weed-check and weed-free environments (e) Chlorophyll contents of Sunflower and Sunflower + Mungbean at different (DAS) in weed-check and weed-free environments (f) Chlorophyll contents of Sole Maize and Maize + Mungbean at different (DAS) in weed-check and weed-free environments (g) Leaf area index (LAI) of Sunflower and Sunflower + Mungbean at different (DAS) in weed-check and weed-free environments (h) Leaf area index (LAI) of Sole Maize and Maize + Mungbean at different (DAS) in weed-check and weedfree environments.

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4. Discussion

The bio-financial viability of mungbean intercropped with sunflower has been considered, revealing that the planting density and oil content of the sunflower were not significantly affected by specific intercropping arrangements. However, factors like plant length, leaf area index, and the number of leaves per plant were significantly impacted (Zhao et al., 2024; Iqbal et al., 2006). Furthermore, the practicality of intercropping vegetables with sorghum was explored, showing that intercropping affects both plant length and seed yield of sorghum. Specifically, the LAI of intercropped sorghum is lower than that of sole-cropped sorghum. This index decreases further when sorghum is intercropped with cluster beans (Rashid et al., 2006). The current study concluded that maize, when grown as a sole crop in a weed-free environment, exhibits optimal growth, resulting in the highest plant length. Conversely, the lowest is observed in weedy conditions due to competition between the crop and weeds. While maize still achieves significant height as a sole crop, intercropping it with mung bean leads to a decrease in plant height. This reduction is attributed to the mungbean’s consumption of nutrients and resources that would otherwise benefit the maize crop, ultimately reducing yield. The research findings indicate that, except for cob length, thousand-grain weight, and harvest index, all parameters studied showed significantly better results in weed-free conditions when maize was grown as a sole crop. Similar results were noted when maize was intercropped or grown in weedy conditions (Fig. 4).

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Fig. 4.

Grain yield comparison of Maize and Sunflower weed-free and weed-check conditions.

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Intercropped soybeans with maize were tested in 2:2 and 4:2 proportions, along with mono-cropped soybeans. The chlorophyll content in intercropped soybeans was significantly lower than that of soybeans grown alone. The same competition dynamics were noted for nutrient consumption between weeds and crops, as well as among crops themselves in a weed-free environment, which suppressed the effect of crops on weeds due to larger canopies. This phenomenon has also been reported by several scientists (Rahimi et al., 2004; Zheng et al., 2022).

Maize, grown as a sole crop, achieves its best in a weed-free condition, resulting in optimal agronomic traits, achieving maximum biological yield, cob diameter, seed yield, and grain quantity. In contrast, when intercropped with mungbean, all these metrics decrease. This decline can be attributed to the mungbean uptake of nutrients that would otherwise benefit the maize crop, leading to reduced yields. In the present research, all parameters studied, except for cob length, thousand-grain weight, and harvest index, showed significant improvements under weed-free conditions and sole cropping. Similar results were observed in the intercropped and weedy check conditions. Similar findings have also been reported by scientists (Azim et al., 2000; Khan and Khaliq, 2003). The study by Ibrar et al. (2002) documented that the leaf area index (LAI) was significantly higher in intercropped systems compared to single crops and showed better results in one-push compared to two-push intercropping combinations. Imran et al. (2011) detailed the yield and yield characteristics of sole sunflowers compared to sunflowers intercropped with mungbean during the spring season. Their research indicated that the height of the plants and the LAI of corn were generally maximized in legume-maize intercropping systems compared to sole maize cultivation (Iqbal and Cheema, 2009; Rana et al., 2001). The results for sunflowers differed significantly from those of maize. When sunflower was grown as a sole crop, they produced better outcomes compared to intercropping with mung beans. The allelopathic nature of mungbean likely contributed to its superior performance in intercropping situations, as sunflower acted mainly as the host crop and faced competition that negatively affected its growth. This is supported by findings acknowledged by Arshad and Ranamukhaarachchi (2012) regarding plant height. Agronomic parameters, including biological yield, head diameter, grain yield, and 1000-grain weight, were documented by Chen et al. (2004). These traits showed significant benefits when sunflower was cultivated as a sole crop in weed-free conditions. In contrast, similar results were obtained under intercropped and weedy conditions documented by Ibrar et al. (2002). The harvest index did not display a significant effect as the weeds compete with plants for nutrition, and the growth of sunflowers in weedy conditions reduces yield, although the impact is less severe than that on maize. This is because sunflowers produce allelopathic chemicals that suppress weeds and reduce competition. Therefore, cultivating crops in a weed-free environment may be more beneficial than in weedy conditions, as reported by Rahimi et al. (2004). The rice-based intercropping systems with cereal and legumes show decreased grain yield but higher total grain yield (Jabbar et al., 2010). Intercropping systems, such as canola-wheat, mustard-garlic, wheat-lentil, mustard-onion, and sunflower-mungbean, have shown higher economic returns compared to sole crops (Sarker et al., 2007; Imran et al., 2011). In terms of bio-economic value, the lower relative yield of the legume intercrop, specifically mungbean, resulted in a higher economic value. This is notable despite the higher relative yields of the base and intermix cereal crops, such as maize and sunflower, which were grown in either weed-checked or weed-free environments, supported by previous literature (Ali and Akram, 1992; Tahir et al., 2003). Weeds, being the most abundant plant species, not only compete with the main crop for nutrients and other inputs but also offer shelter for different pests and diseases. This resulted in impacting crop growth by the release of allelopathic substances into the rhizosphere of the crop plants (Kumar and Chopra, 2013, 2016).

Weeds vary in density depending on the type. Bathu weed did not significantly affect its density when mungbean was intercropped with maize and sunflower; however, the presence of deela weed showed a highly significant impact (Pearson et al., 2016). Sunflower, as a sole crop, produced the highest individual weed density, while when intercropped with mungbean, the Gajar boti had no significant impact on density. The combination of sunflower + mungbean resulted in a greater density of itsit compared to sunflower grown alone. Overall, total weed density was highest when sunflower was grown alone compared to when it was grown with mungbean. This finding is supported by studies conducted by Saucke and Ackermann (2006). Similarly, weed density data were collected at different intervals. The second set of data, taken on day 55, showed consistent results attributed to the allelopathic properties of sunflower and its large canopy, which is also reported by Iqbal et al. (2007). Results of day 75 (DAS) revealed no significant differences in densities for deela, Gajar booti, itsit, weed diversity, total weeds, broad-leafed weeds, grassy-leafed weeds, and total weeds. However, bathu did have a significant effect. The sole sunflower exhibited maximum density compared to the sunflower intercropped with mungbean. On day 95 (20 days intervals), the results indicated that mungbean intercropped with sunflower and maize had no significant effects on the individual weed density. This suggests that as the intervals between measurements increased, a decrease in weed density was observed. The lack of noteworthy effects from intercropping on weed density over time may be due to reduced canopy cover and allelopathic substances as the crops approached maturity, as reported by Weerarathne et al. (2007).

5. Limitations and future directions

The current study was limited to a single season and location. It also did not assess long-term soil health, nutrient cycling, or detailed economic factors beyond yield. Future directions in research should include multi-location trials, assessment of soil microbial activity, and evaluation of nutrient use efficiency under varying fertilizer regimes.

6. Conclusion

The study revealed that growing maize and sunflower as sole crops reduces weed density. Yields under no-weed conditions were significantly higher compared to those in weedy environments. In contrast, mungbean intercropped with maize in a weed-free area achieves a maximum yield compared to the weedy check. However, the yield of sunflowers intercropped with mungbean was less than maize. The findings suggest that maize cultivated alongside mung bean outperforms sunflower, and sole maize also demonstrates better performance than sole sunflower. The primary reason for these effects is that when sunflowers and maize are grown as sole crops, weeds compete for their nutrients. However, when mung bean is grown alongside maize and sunflowers, the weed density decreases because mung bean absorbs the available nutrients. Over time, as days pass, the density of weeds diminishes, leading to changes in crop performance. As weed density decreases, the performance of the crops can also be affected.