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Article

Herbal Companion Crops as an Example of Implementation of Sustainable Plant Protection Practices in Soybean Cultivation

by
Adrian Sikora
1,2,
Joanna Dłużniewska
3,
Bogdan Kulig
1 and
Agnieszka Klimek-Kopyra
1,*
1
Department of Agroecology and Plant Production, University of Agriculture in Kraków, Aleja Mickiewicza 21, 31-120 Kraków, Poland
2
Bayer Sp. Zoo, ul. Aleje Jerozolimskie 158, 02-326 Warszawa, Poland
3
Department of Microbiology and Biomonitoring, University of Agriculture in Kraków, Aleja Mickiewicza 21, 31-120 Kraków, Poland
*
Author to whom correspondence should be addressed.
Agriculture 2024, 14(9), 1485; https://doi.org/10.3390/agriculture14091485 (registering DOI)
Submission received: 9 July 2024 / Revised: 15 August 2024 / Accepted: 20 August 2024 / Published: 1 September 2024
(This article belongs to the Special Issue Advances in the Cultivation and Production of Leguminous Plants)
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Abstract

:
This study aimed to assess the effect of using selected herbs as companion crops in soybean cultivation on the yield and overall health of soybeans. A three-year field experiment (2021–2023) was conducted using a randomized block design with three replications, where the primary experimental variable was the sowing method. The innovative cropping system involved cultivating soybeans alongside different companion herbs, such as alyssum (Lobularia maritima L.), fennel (Foeniculum vulgare Mill.), borage (Borago officinalis L.), French marigold (Tagetes patula L.), calendula (Calendula officinalis L.), and a herbal mixture referred to as ‘MIX’. The study showed that cultivation of soybean with fennel improved the quantitative and qualitative characteristics of the yield, with a significant increase in seed yield (on average by 0.27 t ha−1) as well as protein (7.67%) and oil yield (8.57%) compared to the pure soybean crop. The following fungal diseases were identified during the three-year study period (2021–2023): Cercospora leaf blight, Ascochyta blight, Fusarium wilt, and downy mildew. Cultivation of soybean with herbs as companion crops was implemented to improve the health of soybean to a varied extent. Borage, marigold, and calendula companion crops reduced infection of soybean by the fungi C. kikuchii and F. oxysporum. Cultivation with fennel and marigold was also beneficial for soybean health. On the other hand, cultivation with sweet alyssum and a mixture of herbs increased the occurrence of the fungus A. sojaecola. Cultivation of soybean in association with herbs is legitimate and requires further research given the priorities facing 21st-century agriculture.

1. Introduction

Soybean (Glycine max (L.) Merrill, which belongs to the family Leguminosae is a globally important species. Recent decades have seen a steady increase in global soybean production [1]. According to the United States Department of Agriculture, production of soybean in 2024/2025 is forecast to increase by more than 6% from previous years to a record 422 million tons [2]. Greater demand for soybean comes from globally expanding biodiesel and feedstock production. Worldwide, soybean is used for multiple purposes in various sectors of the economy but it is most important in the fodder industry [3]. In Europe, the increased demand for soybean meal is met by soybean from Argentina, Brazil, and the USA [4]. Despite increasing awareness among farmers about the need to develop domestic protein sources through the promotion of cultivation of all legumes, including soybean, these species do not play a major role in the structure of utility crops. This is due mainly to farmers’ lack of experience with soybean cultivation and its specific requirements. Soybean cultivation in Europe is limited by the length of the growing period and by the weather [5]. Cultivars with a longer growing period predominate in southern Europe, and those with a shorter growing period in central Europe. Soybean is a thermophilic species that requires suitable temperature and water conditions for growth and development. The water requirement of soybean is about 350 mm. Both shortages and surpluses of water negatively affect seed and protein yield [5,6]. Water shortages directly affect soybean yield, while surplus water often affects the health of plants. In central Europe, the health of plants is strongly determined by rainfall distribution [5,7]. Soybean is a plant with relatively high resistance to fungal disease, but recent research indicates that the risk of fungal diseases is increasing [8]. Unfavorable weather directly after the sowing of soybean increases the risk of infection of young seedlings with Fusarium. Unfortunately, as demonstrated by Klimek-Kopyra et al. [8], the extent of the infection of young seedlings with Fusarium is reflected in the subsequent health of soybean plants as they mature. According to the authors, the risk of additional fungal diseases during the growing season is highly correlated with the occurrence of preliminary fungal infection of seedlings. To reduce the preliminary occurrence of fungal diseases such as Fusarium in legume plants, new and effective agrotechnical methods are sought as alternatives to the chemical protection of plants. The use of companion crops can be an effective method of reducing fungal diseases in soybean cultivation. Current research indicates that the use of companion crops is highly effective in the cultivation of other crop plants, including vegetable crops, root crops, and fodder crops [9,10]. Various species are used as companion crops (living mulch) for edible crops, e.g., phacelia, white mustard, radish, sunflower, pea, and lupine [11,12]. The main task of living mulch in the vegetable crop production system is to protect the soil surface against the impact of adverse factors, as well as to improve growth conditions for root plants [13,14]. It protects the soil surface from wind and water erosion [15,16] and also preserves the soil structure by reducing its density. This effect can be attributed to minimized contact between the tractor implements and the soil and the reduced adverse impact of atmospheric factors such as torrential rain or sprinkler irrigation on soil aggregates [17,18].
Other positive aspects of the presence of companion crops include their role in increasing the content of organic matter, better water infiltration, better retention of water and nutrients [13,14,15,16], prevention of water evaporation, and smaller daily fluctuations in soil moisture and temperature. Companion crops reduce the risk of runoff of nutrients and of nitrates and pesticides, thereby preventing pollution of groundwater with these chemicals [19,20].
The use of companion crops is determined by established practices, with certain plant species predominating [9]. Thus far, there has not been widespread attention to the use of medicinal plants for this purpose.
Interest in the cultivation of medicinal and aromatic plants has recently increased in many countries, together with a growing awareness that natural products are healthy, nontoxic, and environmentally safe [21]. Although herbs have great potential in field production, they have not been fully explored. Until now, the use of herbs in soybean production to reduce fungal diseases has not been considered. The urgent need to search for new and more sustainable practices using medicinal and/or aromatic plants in soybean production and protection against pathogens is highlighted. It is assumed that the choice of herb species has an impact on the quantitative and qualitative yield characteristics of soybean and its healthiness.
The aim of this study is to determine the yield and chemical composition of soybean seeds and the health of soybean plants grown together with companion crops as living mulch.

2. Materials and Methods

2.1. Study Location

Empirical data were obtained at the University of Agriculture Experimental Station in Prusy, near Krakow (47°24′ N 7°19′ E, 300 m a.s.l.). The geographic coordinates of the experimental field are 50°07′01″ N and 20°05′19″ E, and it is located 270 m above sea level. The experiment was set up on degraded chernozem (Umbrisols–FAO). This type of soil is fine-grained with moderate amounts of P, K, and Mg, 1.21% organic carbon, and 0.16% total nitrogen.

2.2. Experimental Design

In the years 2021–2023, a single-factor field experiment was set up in a randomized block design in triplicate. The cultivar Merlin from Saatbau Linz, which belongs to the medium-early variety class (000) with high yield stability over the years and high resistance to pathogens, was selected for the study.
The experimental factor was the cropping system. Soybean cv. Merlin was sown alone (‘SOY’) and with companion crops (alyssum ‘ALY’, fennel ‘FEN’, borage ‘BOR’, French marigold ‘MAR’, calendula ‘CAL’, or herbal mixture ‘MIX’) during 3 years of studies. The herbal mixture was composed of the above-mentioned species (alyssum, fennel, borage, French marigold, and calendula). The selection of herb species was determined by the development cycle of soybean plants. Therefore, we selected annual herbs with similar sowing and harvesting dates and growth rates. The plot area was 10 m2. The soybean sowing density was 70 seeds/m2 at 25 cm spacing. Herbs were sown between soybean rows. Alyssum was sown in the amount of 300, fennel in the amount of 70, borage in the amount of 5, marigold in the amount of 30, and calendula in the amount of 15 germinating seeds per 1 m2. In the mixture, the rate of each herb equaled 25%). Species were sown separately. Soybean was sown in the last 10-day period of April in each year of the study using a seed drill. Herbs were sown 2 weeks later when the soybean began the first leaf development using a precision garden seeder. The sowing depth for soybean was 5 cm, whereas herbs were sowed at a depth of 1cm. Inoculation of soybean seeds with Bradryzobium japonicum inoculants Nitragina was conducted directly before sowing. The crops previous to soybean in each year of the study were cereal species. Post-harvest and pre-winter treatments were carried out after harvesting the precursor crop. Mineral fertilizers were applied before sowing, and the field was tilled with a harrow and a cultivator. Mineral fertilizers were applied as follows: ammonium nitrate (34%) at 60 kg·ha−1, potassium chloride (60%) at 120 kg·ha−1, and triple granulated superphosphate (46%) at 80 kg·ha−1. No plant protection products were used, in order to test the potential of soybean cultivation with companion crops. All plants were harvested in the first 10-day period of September.

2.3. Biometric Analysis

For biometric measurements, 20 plants from each treatment were collected and examined in detail, including the determination of shoot length, height of the first pod setting, dry weight of plants, average pod number per plant, average seed number per plant, average pod weight per plant, and average seed weight per plant. Following harvest with a combine, the moisture content of the grain yield and the 1000-seed weight were determined.

2.4. Yield Quality

The yield quality (crude protein and crude oil content) was estimated. The chemical composition of the seeds was determined by near-infrared spectroscopy (NIRS) with an InfraXactTM analyzer (Foss®) (Nils Foss Alle 1 DK-3400 Hillerød Denmark) [22]. N uptake was calculated based on the formula presented by Janket et al. [23]

2.5. Assessment of the Incidence of Cercospora Leaf Blight, Fusarium Wilt, Ascochyta Blight, and Downy Mildew (Peronospora Manshurica) in Soybean Plants

Diseases were identified based on visual symptoms as described in the literature and microscopic observations of causal pathogens. The symptoms of Cercospora leaf blight (Cercospora kikuchii) are reddish-purple spots on the leaves that vary in size from pinpoint spots to larger, irregularly shaped patches [24,25]. The lesions caused by Fusarium oxysporum (Fusarium wilt) appear on plants as interveinal chlorosis, premature defoliation, and wilting [24,25]. The symptoms of Ascochyta blight (Ascochyta sojaecola) are dark brown spots on the surface of the leaves that increase in size. The spots have a lighter center, and the round, black fruiting bodies of the fungus are visible to the naked eye [24,25]. The symptoms of downy mildew (Peronospora manshurica) are visible on the leaves. The first symptoms on newly infected plants appear in June, on the upper surface of the leaf blades, in the form of small yellow-green spots, which may grow larger and turn grey. When humidity is high, a greyish coating (the mycelium of the pathogen) may be visible on the underside of the leaves, underneath the spots.
The health status of the soybean plants was evaluated at the end of the flowering stage (BBCH stage 69) and at the pod and seed development stage (BBCH stage 89). Disease severity was determined in 20 sample plants in the middle rows of each plot. Plants were evaluated visually for disease severity, which was rated on a scale of 0 to 4: 0 = no symptoms or lesions; 1 = minor lesions present on 1% to 10% of the leaf; 2 = lesions present on 11% to 25% of the leaf; 3 = 26% to 50% of the leaf; 4 = lesions covering 51% or more of the leaf and withered and dead leaves. The disease index (DI) was calculated for the diseases as a percentage, where
DI (%) = [sum (class frequency × score of rating class)]/[(total number of plants) × (maximum scale value)] × 100.
The visual assessment of disease was confirmed in the laboratory. Infected stem tissue samples from wilted plants and leaf samples from plants showing typical disease symptoms were taken to the laboratory. Pathogens were identified under a microscope using aqueous mounting media. Fungal species were identified on the basis of mycological keys and monographs [26]. Identification of each isolate was conducted twice.

2.6. Statistical Analysis

A two-factorial analysis of variance (ANOVA) was performed with study years (random) and method of sowing (experimental) as the factors, with subsequent multiple comparisons of means, using Statistica version 13.1. Means were separated by least significant differences (LSD) when the F-test indicated factorial effects at p < 0.05. The main effects are noted within the tables. Significant factor interactions are shown by p-value.

3. Results

3.1. Weather Conditions

The weather in the years 2021–2023 was characterized on the basis of 10-day values for selected meteorological elements, i.e., average air temperature, precipitation totals, and the number of days with rainfall from April to September. Daily data pertaining to the meteorological elements obtained from the University of Agriculture station in Prusy near Krakow were used.
The weather during the three-year period was highly varied. The most rainfall was recorded in the year 2021, which was classified as very wet. The rainfall total in the growing season (April–September) exceeded 600 mm. The most abundant rainfall was recorded in July and August. Less rainfall was recorded in 2022 than in 2021. A shortage of rainfall was noted, mainly in May, during the emergence of plants, and in the first and second 10-day periods of August during seed formation. The year 2023 was optimal in terms of temperature and rainfall conditions for soybean cultivation. The rainfall total for the entire growing period was 485 mm, and the average air temperature was 16.2 °C. The rainfall distribution among the months was favorable to the development of the plants.

3.2. Biometric Traits

The use of herbs as companion crops in soybean cultivation only slightly modified the morphological characteristics of soybean. Only minor variations were observed in the height of the plants and the height of the first pod setting. The presence of companion crops in the soybean crop significantly slowed down the growth of the plants, resulting in plants that were shorter, on average, by 2–3 cm. In addition, in some cases (cultivation with fennel) lower setting of the first pod was observed, on average, by 2 cm. Only the cultivation of soybean with the mixture of herbs increased the height of the first pod setting, on average, by 1 cm.
The weather significantly influenced the morphological characteristics of soybean (Table 1). Values for the morphological traits analyzed were significantly greater in 2023 (optimal in terms of temperature and rainfall) and significantly lower in 2022 (periodic rainfall shortage). In 2023, the weather during the entire growing season led to high pod and seed productivity. Soybean plants formed, on average, 48.2 pods per plant and 112 seeds weighing 27.7 g. The significant amount of rainfall in May of 2023 led to a low setting of the first pod (10 cm) in comparison to the previous years when lower levels of rainfall resulted in a higher setting of the first pod (about 14 cm).
In 2022, with a periodic water shortage, the plants were less productive, resulting in the formation of far fewer pods and seeds per plant, with lower weight.
The statistical analysis revealed a significant interaction of the factors (years and soybean cropping system) on the morphological features of the plants (Table 2, Figure 1). The weather conditions (rainfall distribution in the growing season and average air temperature) in 2023 caused a significant increase in certain traits of the soybean plants (seed number, pod number, and seed and pod weight) grown with fennel or alyssum in comparison with the pure soybean crop. The presence of other companion crops had no effect on these morphological traits. Significantly lower parameters (seed and pod number and weight) were noted in 2022. Only the height of the first pod setting was positively influenced by the weather conditions in 2022 compared to 2023.

3.3. Seed Yield and Yield Quality

Soybean yield was significantly influenced by experimental factors (Table 3). Both factors (fixed and random) had a very strong influence on the soybean yield, as the difference was 0.56 t ha−1 and 1.86 t ha−1, respectively. Among the companion crops compared in the study, the highest yields were obtained for soybean grown together with fennel (3.95 t ha−1) and the lowest for soybean grown with the mixture of herbs (3.39 t ha−1). The year 2023 was the most favorable for the plants, with the highest yields (4.82 t ha−1), while the year 2022 was the least favorable (2.96 t ha−1). The yields of protein, oil, and starch did not depend significantly on the choice of companion crop. However, the protein yield showed a tendency to increase when soybean was grown with fennel or borage. A similar tendency was noted for the efficiency of nitrogen uptake by the seeds. Similarly, significantly more nitrogen was fixated by soybean plants grown with fennel or borage than in the pure soybean crop. No significant interaction between the year and soybean cropping system was noted. The weather conditions significantly influenced the seed yield, the protein, oil, and starch yield, and the efficiency of nitrogen uptake (Table 3).

3.4. Pathogen Suppression

Variation in infection of the soybean plants was observed during the study period (Figure 2, Figure 3, Figure 4, Figure 5 and Figure 6). The highest infection, in 2023, was caused by Ascochyta blight and downy mildew (Figure 2b,d), while in 2023, infection of Fusarium wilt and Cercospora leaf blight were not detected (Figure 2a,c). In contrast, in the years 2021 and 2022, infection with Fusarium wilt, Ascochyta blight, and Cercospora leaf blight were observed at the end of the flowering stage (BBCH 69) and at the pod maturation stage (BBCH 89) (Figure 3, Figure 4 and Figure 5). The weather in 2021 significantly contributed to the infection of plants by fungi of the genera Fusarium and Cercospora. Infection was more severe in soybean grown alone or with ALY as the companion crop (Figure 2a,c). The cropping system significantly influenced the degree of infection of plants by Cercospora, which was highest in soybean grown with ALY and lowest in the crop grown with MIX (year 2022) (Figure 2c). In the case of downy mildew, the cropping system did not cause significant variation in the degree of infection of plants (Figure 2d).
In both 2021 and 2022, infection of plants was significantly greater at BBCH 89 (pod and seed development) (Figure 3). During the three-year study period, 2023 was the only year in which diseases caused by the pathogen F. oxysporum were not observed. In the earlier period (2021–2022), Fusarium wilt was highly severe in 2021. Soybean cultivation with herbs significantly decreased infection of plants with the fungus F. oxysporum (Figure 3) compared to the pure soybean crop. The protective effect of cultivation with herbs was stronger in 2022 (Figure 3b). In that year, soybean cultivation with all companion crops significantly decreased the F. oxysporum disease index at BBCH 89 (pod and seed development) (Figure 3b). The soybean plants grown with the herbal mixture (MIX) were the least infected (Figure 3b). However, it was noted that soybean cultivated with fennel, borage, marigold, and calendula had significantly improved plant health.
During the three-year study period, low severity of Ascochyta blight was observed; the disease index did not exceed 9% (Figure 4). The disease was more severe in 2023 (Figure 4a). A slightly smaller infection was noticed in BBCH stage 69. Soybean cultivation with herbs limited the occurrence of disease, but this effect was not statistically significant (Figure 4b,c). In the 2021–2022 years of the study, in BBCH 89, the cultivation of soybean with sweet alyssum and the herbal mixture increased the A. sojaecola disease index (Figure 4a,b).
Cercospora leaf blight was significantly more severe in 2021 (Figure 5a) and less severe in 2022, while it was not observed at all in 2023. In both 2021 and 2022, infection was significantly greater at BBCH stage 89 (Figure 5). In 2021, cultivation of soybean with herbs (FEN, CAL, and MIX) reduced infection of the plants with C. kikuchii (Figure 5a). Only cultivation with sweet alyssum increased the severity of the disease (Figure 5). The statistical analysis showed that in 2022, soybean grown in a mixture with herbs resulted in healthier plants (Figure 5). Soybean plants grown with fennel, calendula, and a mixture were the healthiest (Figure 5).
Downy mildew was observed only in 2023 (Figure 6). The field observations showed that infection of plants was slightly greater at BBCH 89 (50–60% of disease index), but this was not confirmed statistically (Figure 6). Soybean cultivation with herbs did not influence the degree of infection by the pathogen.
At BBCH 69 in 2021, growing soybean with almost all herbs reduced the incidence of Cercospora leaf blight and Fusarium wilt, except in the ALY crop (Figure 7a). In 2022, on the other hand, soybean with herbs reduced Cercospora leaf blight with all herbs. The index of plant infection with the fungi F. oxysporum and A. sojaecola was low, therefore, no positive effect of the addition of herbs was observed (Figure 7a).
At BBCH 89, in the wet year of 2021, soybean cultivation with herbs (FEN, BOR, CAL, MIX) was effectively protected against Cercospora leaf blight (Figure 7b), whereas soybean cultivated in MIX was effectively protected against Fusarium wilt. The plant infection index for the fungus A. sojaecola was low. Soybean cultivation with FEN, BOR, or CAL resulted in the absence of Ascochyta blight. In contrast, in the year 2022, growing soybean with selected herbs (FEN, BOR, CAL, or MIX) improved plant health against Cercospora leaf blight. The plant infection index by the fungus F. oxysporum was particularly low for soybean with MIX, followed by BOR, MAR, and CAL. On the other hand, no positive effect was observed for protection against Ascochyta blight, which occurred at low intensity during this year (Figure 7b).

4. Discussion

4.1. Companion Crop and Seed Yield

Cultivation of soybean with companion crops resulted in an increase in soybean seed yield. Among the companion crops compared in the study, the best effects were obtained when soybean was grown with fennel, with a difference of 0.27 t ha−1 relative to the sole crop of soybean. Soybean plants accompanied by herbs were shorter, and the setting of the first pod was significantly lower, which is unfavorable in terms of combine harvesting and leads to substantial yield losses. This was due to the effect of interspecific competition, which, according to the literature [27,28], often influences the habits of accompanying plants. The presence of companion crops in soybean cultivation was highly beneficial for elements of the yield structure of soybean. Significantly more pods and seeds were formed, and the seed weight was significantly higher in the crops grown with herbs. The most beneficial companion crop for soybean was fennel, which had a stimulating effect, while the least beneficial was the mixture of herbs.
In addition, the inclusion of fennel in soybean cultivation had a positive impact on soybean quality. Significantly higher yields of protein, oil, and starch were obtained for soybean accompanied by this species. Soybean plants in this configuration also took up more nitrogen from the soil. In previous research on intercropping of fennel with common bean, the only positive effect of fennel was an improvement in the quality of the crop. Rezaei-Chiyaneh et al. [29] tested the intercropping of fennel and common bean and showed significantly higher yields of both plants in the pure crops. However, increasing the proportion of fennel in the mixture with bean (3:2) significantly improved the oil content and the fatty acid profile of the fennel seeds. Interesting intercropping experiments with licorice (Glycyrrhiza glabra L.) and wheat (Triticum spp.) or barley (Hordeum vulgare L.) have been conducted in southern Italy. The results of such experiments are varied, but they are generally favorable only for cereal crops [30,31]. According to Carruba et al. [32], in the cultivation of medicinal and aromatic plants, while productivity is important, it is not the only aspect that should be taken into account. In this special type of cultivation, particular attention should be focused on qualitative traits. Varied results for the qualitative aspect of production have been obtained in intercropping, with many studies showing that, in some cases, this technique may influence the chemical properties of the accompanying species, leading to differences in the yield of essential oils as well as in the composition of extracts.
For example, the content of alkaloids in jimsonweed plants (Datura stramonium L.) seems to be influenced by accompanying species such as white lupin (Lupinus albus L.) or peppermint (Mentha piperita L.). Morelli [33] showed that the choice of species can positively or negatively affect productivity. Maffei and Mucciarelli [34] showed that the content of essential oil and the content of menthol in peppermint oil are positively influenced by intercropping with soybean (Glycine max Merr.).

4.2. Companion Crops and Soybean Health

In our study, the following diseases were observed in 2021 and 2022: Cercospora leaf blight, Fusarium wilt, Ascochyta blight, and powdery mildew. Cercospora leaf blight and Fusarium wilt posed a greater threat, while Ascochyta blight was not severe. The occurrence of all diseases increased during the pod and seed development stage. Cultivation of soybean with herbs in most treatments improved the health of the soybean plants. However, the influence of herbs on individual pathogens was varied. Borage and calendula reduced infection of soybean by fungi C. kikuchii and F. oxysporum. Cultivation with fennel and marigold was also beneficial for the health of soybean. However, cultivation with sweet alyssum and the herbal mixture increased the occurrence of A. sojaecola.
Intercropping of pea with medicinal plants as a means of natural disease control is discussed by Gehad [35]. Intercropping of pea with medicinal plants, i.e., fennel, caraway, dill, and anise, was effective at decreasing the severity of downy mildew. The reduction in infection with wilt and root rot under intercropping conditions may be due to root exudates of the plants, which changed the total microbial count in the rhizosphere [36]. El Gindy [37] reported that intercropping of four faba bean cultivars individually with each of four medicinal plants—fenugreek, coriander, anise, and caraway—under field conditions decreased the incidence of chocolate spot compared to the control due to the effect of the odors of the plants, with the best effects obtained for fenugreek and coriander. Sahar [38] also reported that intercropping of faba bean with each of three plants—onion, garlic, and caraway—significantly reduced the severity of chocolate spot caused by B. fabae under greenhouse and field conditions.

5. Conclusions

Cultivation of soybean with fennel improves the quantitative and qualitative parameters of the seed yield. The seed yield increased significantly, by 0.27 t ha−1, compared to the pure soybean crop. Cultivation of soybean with herbs improves the health of soybean to a varying extent. Borage and calendula reduced infection of soybean by fungi C. kikuchii and F. oxysporum. Cultivation with fennel and marigold also positively influenced the health of soybean. On the other hand, cultivation with sweet alyssum and the herbal mixture increased the occurrence of A. sojaecola.
Presently, agriculture faces the challenge of developing sustainable practices in legume cultivation. Assuming that EU agricultural policy will reduce pesticides in agricultural production, an opportunity should be seen in the biodiversity of agroecosystems. These findings prove that herbal plants can be a viable support for soybean cultivation. However, further research is needed to optimize the sowing parameters and proper selection of herbs as companion crops for the required growing conditions of soybean.

Author Contributions

Conceptualization, A.S. and A.K.-K.; Methodology, A.S., J.D. and A.K.-K.; Validation, J.D., B.K. and A.K.-K.; Formal analysis, A.S., B.K. and A.K.-K.; Investigation, A.S. and A.K.-K.; Resources, J.D. and A.K.-K.; Writing—original draft, A.S., J.D. and A.K.-K.; Writing—review and editing, A.K.-K., J.D., A.S. and B.K.; Supervision, A.K.-K. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the Ministry of Science and Higher Education of the Republic of Poland.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

All data are contained within the article.

Conflicts of Interest

Author Adrian Sikora was employed by the company Bayer Sp. Zoo. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Agriculture 14 01485 g001aAgriculture 14 01485 g001b
Figure 1. Effect of the interaction of years and cropping system on (a) plant height, (b) height of first pod setting, (c) pod number, (d) seed number, (e) pod weight, (f) seed weight per plant. Means in columns with different letters are significantly different (p < 0.05).
Figure 1. Effect of the interaction of years and cropping system on (a) plant height, (b) height of first pod setting, (c) pod number, (d) seed number, (e) pod weight, (f) seed weight per plant. Means in columns with different letters are significantly different (p < 0.05).
Agriculture 14 01485 g001aAgriculture 14 01485 g001b
Agriculture 14 01485 g002aAgriculture 14 01485 g002b
Figure 2. Effect of the interaction of year and soybean cropping system on the occurrence of (a) Fusarium wilt, (b) Ascochyta blight, (c) Cercospora leaf blight, and (d) downy mildew during the three-year period (2021–2023). Means in columns with different letters are significantly different (p < 0.05).
Figure 2. Effect of the interaction of year and soybean cropping system on the occurrence of (a) Fusarium wilt, (b) Ascochyta blight, (c) Cercospora leaf blight, and (d) downy mildew during the three-year period (2021–2023). Means in columns with different letters are significantly different (p < 0.05).
Agriculture 14 01485 g002aAgriculture 14 01485 g002b
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Figure 3. Occurrence of Fusarium wilt depending on the developmental stage of soybean in (a) 2021 and (b) 2022. Means in columns with different letters are significantly different (p < 0.05).
Figure 3. Occurrence of Fusarium wilt depending on the developmental stage of soybean in (a) 2021 and (b) 2022. Means in columns with different letters are significantly different (p < 0.05).
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Agriculture 14 01485 g004
Figure 4. Occurrence of Ascochyta blight depending on the development stage of soybean in (a) 2021, (b) 2022, and (c) 2023. Means in columns with different letters are significantly different (p < 0.05).
Figure 4. Occurrence of Ascochyta blight depending on the development stage of soybean in (a) 2021, (b) 2022, and (c) 2023. Means in columns with different letters are significantly different (p < 0.05).
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Figure 5. Occurrence of Cercospora leaf blight depending on the development stage of soybean in (a) 2021 and (b) 2022. Means in columns with different letters are significantly different (p < 0.05).
Figure 5. Occurrence of Cercospora leaf blight depending on the development stage of soybean in (a) 2021 and (b) 2022. Means in columns with different letters are significantly different (p < 0.05).
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Agriculture 14 01485 g006
Figure 6. Occurrence of downy mildew depending on the development stage of soybean in 2023.
Figure 6. Occurrence of downy mildew depending on the development stage of soybean in 2023.
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Figure 7. Effect of the interaction of year and soybean cropping system on the occurrence of Fusarium wilt, Ascochyta blight, and Cercospora leaf blight at the (a) BBCH 69 and (b) BBCH 89.
Figure 7. Effect of the interaction of year and soybean cropping system on the occurrence of Fusarium wilt, Ascochyta blight, and Cercospora leaf blight at the (a) BBCH 69 and (b) BBCH 89.
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Table 1. Weather during the soybean growing season (2021–2023).
Table 1. Weather during the soybean growing season (2021–2023).
ParameterDecada *Apr.MayJun.Jul.Aug.Sep.Σ/Mean
2021
Temperature15.1210.3516.522.5319.7715.21
24.8814.4419.521.8720.1915.85
37.3313.3422.3621.8316.013.15
Mean 5.7812.7119.4722.0818.6514.7415.57
Rainfall16.414.24.827.21161.2
234.154.67.8102.824.431.2
39.628.878.829.985.414.4
Σ50.197.691.4159.9225.846.8671.6
2022
Temperature14.0211.8416.5418.4419.0313.48
24.6414.7417.0617.0520.0411.32
38.1212.7820.6419.9018.38.96
Mean 5.5913.1218.0818.4519.1411.2514.27
Rainfall124.611.043.657.20.4024.4
26.200.0029.610.68.6023.0
314.89.400.0044.275.220.9
Σ45.620.473.211284.268.3403.7
2023
Temperature13.4910.51720.417.217.9
29.5612.316.821.322.719.0
310.715.819.518.920.917.3
Mean 7.9012.917.820.220.318.116.2
Rainfall120.239.60.229.671.820.2
220.650.042.042.20.0028.6
313.00.4023.634.225.823
Σ53.990.065.810697.671.8485.1
* decada—a period of ten days of the month.
Table 2. Morphological characteristics of soybean plants depending on the cropping system.
Table 2. Morphological characteristics of soybean plants depending on the cropping system.
TreatmentHeight of Plant (cm)Height of 1st Pod (cm)No of Pods per PlantNo of Seeds per PlantWeight of Pods (g)Weight of Seeds (g)1000 Seeds Weight (g)
Year (Y)202180.4 b14.28 a40.2 c91.8 b20.1 b14.0 b162.5 b
202257.5 c14.02 a20.6 b45.8 c10.3 c6.95 c152.4 c
202395.0 a10.34 b48.2 a112.0 a 27.7 a19.7 a175.2 a
p < 0.05<0.000 *<0.000 *<0.000 *<0.000 *<0.000 *<0.000 *ns
Way of sowing (WS)SOY81.4 a13.3 ab35.688.718.913.3 ab168.8
ALY79.5 ab13.5 a37.284.420.915.7 a170.0
FEN74.9 ab11.3 b39.490.620.714.4 ab156.8
BOR72.7 b12.6 ab34.478.118.312.9 ab163.8
MAR78.3 ab12.5 ab36.781.219.311.7 b160.9
CAL76.0 ab12.6 ab38.788.620.514.4 ab159.9
MIX80.6 ab14.5 a32.371.417.211.9 b164.4
p < 0.05<0.007 *<0.002 *nsnsns<0.049 *ns
Y × WS p < 0.05<0.031 *<0.000 *<0.000 *<0.009 *<0.01 *<0.004 *ns
*—significant difference at α = 0.05, Letters represent significant differences (Tukey’s multiple range test); ns—not significant.
Table 3. Soybean seed yield, protein yield, oil yield, starch yield, and N uptake depending on the year and the cropping system.
Table 3. Soybean seed yield, protein yield, oil yield, starch yield, and N uptake depending on the year and the cropping system.
TreatmentSeed Yield
(t ha−1)		Protein Yield (kg ha−1)Oil Yield
(kg ha−1)		Starch Yield
(kg ha−1)		N Uptake
(kg t−1)
Year (Y)20213.34 b1135.4 b649.4 b1218.8 b181.6 b
20222.96 c1047.8 b576.8 c1017.4 c167.6 b
20234.82 a1767.3 a897.2 a1698.0 a 282.8 a
p < 0.05<0.000 *<0.000 *<0.000 *<0.000 *<0.000 *
Way of sowing (WS)SOY3.68 ab1302.3707.61269.3208.4
ALY3.70 ab1295.4689.91310.8207.3
FEN3.95 a1402.2768.31434.3224.4
BOR3.44 b1360.5721.51359.9217.7
MAR3.41 b1254.6697.91235.2200.7
CAL3.46 b1288.9703.21293.5206.2
MIX3.39 b1313.9665.91277.1210.2
p < 0.05<0.000 *nsnsnsns
Y × WSp < 0.05nsnsnsnsns
*—significant difference at α = 0.05. Letters represent significant differences (Tukey’s multiple range test); ns—not significant.
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Sikora, A.; Dłużniewska, J.; Kulig, B.; Klimek-Kopyra, A. Herbal Companion Crops as an Example of Implementation of Sustainable Plant Protection Practices in Soybean Cultivation. Agriculture 2024, 14, 1485. https://doi.org/10.3390/agriculture14091485

AMA Style

Sikora A, Dłużniewska J, Kulig B, Klimek-Kopyra A. Herbal Companion Crops as an Example of Implementation of Sustainable Plant Protection Practices in Soybean Cultivation. Agriculture. 2024; 14(9):1485. https://doi.org/10.3390/agriculture14091485

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Sikora, Adrian, Joanna Dłużniewska, Bogdan Kulig, and Agnieszka Klimek-Kopyra. 2024. "Herbal Companion Crops as an Example of Implementation of Sustainable Plant Protection Practices in Soybean Cultivation" Agriculture 14, no. 9: 1485. https://doi.org/10.3390/agriculture14091485

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