https://orcid.org/0000-0002-7666-0748
ABSTRACT
The aim of the study was to verify the hypothesis that intercropping of soybean with buckwheat will positively affect yielding parameters and nutritional value of soybean seed. The experimental scheme assumed intercropping of two soybean cultivars alternately with one and two rows of buckwheat. The control (C) was soybean in monoculture. Both Annushka and Mavka cultivars significantly increased seed yield in the intercropping system with one row of buckwheat as compared to control. The addition of two rows of buckwheat resulted in a significant decrease in seed yield of both soybean cultivars compared to control. The seeds of both cultivars had significantly higher fat content and better fatty acid composition in both variants of intercropping with buckwheat compared to soybean monoculture. Significant changes in the amino acid composition were noted in the seeds of Mavka cultivar, in which glutamic and aspartic acids were the most abundant and the cultivation with two rows of buckwheat additionally increased their content. Intercropping of soybean with buckwheat significantly reduced weed infestation in both tested soybean cultivars. The presented results confirm the assumed hypothesis and the most advantageous variant turned out to be the cultivation of soybean with one row of buckwheat.
Introduction
Nowadays, most agricultural systems are based on the cultivation of plants in monoculture often lasting even several years. This raises concerns about reduced environmental services and soil degradation (Tilman et al. Citation2002; Brooker et al. Citation2015). An alternative can be agricultural systems connecting several species to cultivation simultaneously as a practical application of organic farming principles based on positive plant interactions to sustainable agriculture. This systems are called ‘intercropping’ or more precisely ‘relay-strip intercropping’ (Vandermeer et al. Citation1998; Martin-Guay et al. Citation2018).
The intercropping is a system whereby two or more species of crops are sown or planted simultaneously in the same field and in the same growing season (Li et al. Citation2001; Bedoussac et al. Citation2015). The advantages resulting from such a cultivation method are the reduction of biotic and abiotic environmental stresses on yielding and including primarily protection of soil against erosion and excessive water evaporation from the soil. This idea was born in India, Latin America and South-East Asia (Buczkowska and Rochalska Citation2010; Wang et al. Citation2017). When planning mixed cultivation of several plant species at the same time, attention should be paid to the possible adverse effects of plant allelopathic activity, light distribution among the crops, root system structure, development and growth rate, but at the same time botanical distinctiveness should be preserved. One of the basic disadvantages of intercropping is inter-species competition for water, nutrients and space for the development of aboveground parts and roots of plants (Hauggaard-Nielsen and Jensen Citation2005; Pronk et al. Citation2003; Bedoussac et al. Citation2015; Brooker et al. Citation2015; Gou et al. Citation2017). The effect of the competition of Fabaceae plants with cereals is a reduction in the yield of legume and cereal seed. Deterioration of growth and morphological changes, such as the production of fewer pods, may be due to shading by a second species. This is also due to the fact that cereals are more competitive than leguminous plants their nitrogen uptake from the soil due to faster root development and higher demand for this component. Growing plants together with species with strongly dominant properties reduces their yield. The yield of Fabaceae species is lower than in pure sowing, but the total yield with a cereal plant is higher in intercropping compared to the cultivation of these plants in monoculture. In the intercropping with well selected species, inter-species competition has a stimulating effect on both cultivated species or at least one of them. This is manifested by the increased quantity and quality of the yield. The intercropped maize with legumes has better access to soil N than sole maize. Growing an oilseed plant together with a Fabaceae plant increases the lipid content of the seeds of the oilseed species, improves the amino acid composition and fatty acid profile of both species (de Lacerda et al. Citation2003; Corre-Hellou et al. Citation2006; Muoneke et al. Citation2007; Liu et al. Citation2016; Klimek-Kopyra et al. Citation2017).
Change in the chemical composition of plant seeds is not the only advantage of intercropping. This technique significantly reduces the weed infestation of the field, which can contribute to reducing or eliminating the use of herbicides. Some combinations of mixed cultivation reduce the occurrence of pests and diseases (Trenbath Citation1993; Hauggaard-Nielsen et al. Citation2001).
One of the components most commonly used in intercropping are leguminous plants with different crops of similar morphology, growth and development. The most data concerns maize cultivation with soybean (Głowacka Citation2007; Sürmen and Kara Citation2017). However, there are few reports on the intercropping of buckwheat and soybean. Therefore, the aim of the study was to verify the hypothesis that the intercropping with buckwheat will have a positive effect on the quantitative and qualitative parameters of soybean yielding and weed infestation of the field in comparison with soybean monoculture.
Materials and methods
The study was carried out in 2018 on a farm located in Liśnik Mały (50°53′25,13″N 22°05′36,77″E). The field experiment was established using the ‘split-plot’ method, blocked into rectangular strips measuring 2.7m x 40m on lessive soil, made of loess. The soil reaction was slightly acidic (pHKCl of soil was 6.7). The content of macroelements in the soil was as follows: phosphorus 12.1; potassium 28.4 and magnesium 6.9 mg/100g soil. The microelements content in the soil was: boron 0.14; copper 0.12; zinc 0.46; manganese 14.58 and iron 71.0 mg/100g of soil.
The total precipitation in April was 50.8 mm, while in May a slightly lower total precipitation (48.5 mm) was recorded. In the subsequent months of the vegetation period, both the sum of precipitation and average temperatures were similar to multi-year averages and were suitable for the requirements of soybean and buckwheat. The low precipitation in August (38.4 mm) contributed to the uniform ripening of soybean plants. Before sowing, 18 kg NH4·ha−1, 60 kg P2O5·ha−1, 90 kg K2O·ha−1 and 21 kg SO3·ha−1 was brought into the soil. Soybean of Mavka and Annushka cultivars and buckwheat of Kora cultivar were sown in the first decade of May. Soybean seed was grafted with nitragine (Rhizobium japonicum).
The study tested the effect of two variants of narrow configuration strip intercrops soybean with buckwheat on yielding parameters and weed infestation of two soybean cultivars in relation to standard soybean cultivation. In the first variant (S1), the spacing of soybean rows was 25 cm and 1 row of buckwheat was sown between them. In order to study the reaction of soybean to intercropping in a wider range, investigated two cultivars with different characteristics of plant growth. The sowing standard of Mavka soybean was 126 kg·ha−1 (68 plants per m2; mass of a thousand seeds = 129 g) and in case of Annushka cultivar it was 113 kg·ha−1 (84 plants per m2; mass of a thousand seeds = 178 g). The difference in sowing standard between soybean cultivars results from differences in plant conformation and such sowing standards are used in practice for these cultivars of soybean. Mavka is a cultivar with a higher tillering and growth than Annushka, therefore, in order to obtain similar canopy density the sowing rate was reduced for Mavka. The sowing standard of buckwheat in this arrangement was 15 kg·ha−1 (56 plants per m2). In the second variant (S2), 2 rows of buckwheat were sown between rows of soybean (also at 25 cm spacing). The sowing standard of Mavka soybean was 104 kg·ha−1 (56 plants per m2) and Annushka – 102 kg·ha−1 (76 plants per m2). The sowing standard of buckwheat in this arrangement was 20 kg·ha−1 (density of 74 plants per m2). Sowing of two different plant species was performed with a modified traditional seed drill. The control (C) was soybean in monoculture. The sowing standard of Mavka soybean was 156 kg·ha−1 (84 plants per m2) and Annushka soybean – 129 kg·ha−1 (96 plants per m2). To obtain the similar total canopy density in all variants of experiment, changes in the sowing standards and density of soybean and buckwheat plants were necessary. The intercropping and monoculture did not assume chemical protection of the crop.
The experiment was carried out to determine the following resultant features: plant height and height of the first soybean pod deposition, soybean seed yield, weight of one thousand seeds, protein content on the OmegAnalizer NIR (near infrared) grain analysers, fatty acid compositions (by the CLB/GC/3/2019 version 4 of 01.04.2019) and amino acids (by the CLA/PLC/34/2019 version 3 of 01.04.2019). Weed infestation of the soybean field was assessed using the quantitative and weighting method before harvesting soybeans. The results of the study were statistically elaborated by means of variance analysis. The mean values were compared using Tukey’s test at the significance level p = .05.
Results
The experimental factor, which were two variants of soybean intercropping with buckwheat (S1 – 1 row of soybean + 1 row of buckwheat, and S2 – 1 row of soybean + 2 rows of buckwheat) significantly changed most of the soybean yielding parameters with respect to soybean cultivation in monoculture (control – C). Both cultivars had significantly higher seed yields in S1 as compared to C. Variant S2, on the other hand, caused a decrease in seed yield compared to C and S1. These differences were also statistically significant and only in the case of Annushka cultivar the differences between variant S2 and C had a tendency nature ().
Table 1. Seed yield (dt·ha−1); plant height (cm); height of the first pod (cm); number of pods (pcs/plant); and weight of one thousand seeds (g) of soybean.
Regardless of the cultivar, no statistically significant differences in the height of soybean plants between intercropping variants (S1 and S2) and C were proved. However, it was noted that plants from variant S1 were higher than from C. In turn, soybean plants from S2 were lower than plants from C. Significant differences in soybean plant height were noted between S1 and S2 (). The height of the first pod and the number of productive pods changed significantly only for the Mavka cultivar, which had a higher first pod and a higher average number of pods in variant S1 than in C and variant S2. In both soybean cultivars, the experimental factor did not have a significant effect on weight of one thousand seeds. However, soybeans from S1 and S2 showed a tendency to have a lower weight of one thousand seeds than seeds from C ().
The intercropping did not differentiate the protein content of the seeds of both a cultivars. However, significant differences were noted in the fat content and fatty acids profile. Regardless of the soybean cultivar, the seeds from variants S1 and S2 were characterised by significantly higher content of fat and fatty acids from the saturated (SFA) monounsaturated (MUFA) and polyunsaturated (PUFA) groups as well as from the omega 3, 6 and 9 groups as compared to C. When analysing the fatty acid profile of soybean seeds it was found that the dominant fatty acids in the seeds of both cultivars were polyunsaturated fatty acids (PUFA) and omega 6 and the lowest contents were determined for omega-3 acids ().
Table 2. The content of protein (%), fat (%) and fatty acid profile (g·100 g−1) in soybean seeds.
Significant changes in the content of amino acids in seeds under the influence of the examined factor were recorded in Mavka cultivar. In the variant of S2 of intercropping, significantly higher contents of all amino acids in relation to C were determined. In the case of Annushka cultivar, the experimental factor significantly differentiated only the content of valine, lysine and arginine, where their contents were lower in S1 and S2 than in C. Regardless of the cultivar, soybeans contained the most glutamic and aspartic acids. On the other hand, the lowest content was determined for histidine ().
Table 3. Amino acid composition in soybean seeds (mg·g−1).
The pre-harvest soybean weed control showed that the air-dry weed weight and total weed count in both tested soybean cultivars decreased significantly in both intercropping variants compared to the control (). The most numerous weeds belonged to the dicotyledonous group. Commonly occurring species from this group were: Chenopodium album, Spergula arvensis, Cerastium holosteoides, and Brassica napus. These were the main weeds in the soybean field. There were only two species from the group of monocotyledonous species: Echinochloa crus-galli and Setaria glauca. In the S1 and S2 intercropping variant, the number of weed species was the lowest, and 6–8 dicotyledonous weed species were observed. The most numerous species were: Chenopodium album, Brassica napus and Amaranthus retroflexus. From the monocotyledonous group, on the other hand, from 1 to 2 species were identified and they were Echinochloa crus-galli and Setaria glauca ().
Table 4. Air-dry weight (g·m−2) and number of weeds (pcs·m−2) in canopy of soybean and buckwheat.
Table 5. Species composition and number of weeds (pcs·m−2) in canopy of soybean and buckwheat.
Discussion
In the experiment, the reaction of soybean to intercropping with buckwheat and the influence of this cultivation method on yielding and weed infestation of this species were evaluated. In the presented studies, the highest yield of soybean was obtained with one row of buckwheat (S1, ) and it was significantly higher than in soybean monoculture. It was probably due to the limitation of weed infestation by buckwheat in relation to the soybean monoculture ( and ), where the weed infestation was relatively high. Two rows of buckwheat limited the soybean yield in relation to the soybean monoculture, therefore one row of buckwheat in soybean can be considered optimal for this intercropping system. The results of Cheriere et al. (Citation2020) showed that the soybean yield in the intercropping with buckwheat was significant lower than sole soybean total yield in intercrop. Also the total yield in their research (soybean + buckwheat) was lower than the sole crop soybean yield, but the differences were insignificant. The differences between our results and Cheriere et al. (Citation2020) results can be explained by about twice as high weed infestation in the soybean monoculture in our study, which was significantly reduced by buckwheat. In the study by Żabiński (Citation2008) concerning the intercropping of lentil with supporting components in the form of yellow lupine and buckwheat, it was found that the highest yields of lentil were obtained by cultivating lentils with buckwheat. In addition, the authors showed that the intercropping significantly reduced the field bedding, it also increased the height of the first pod, thus reducing the losses during mechanical harvest as compared to lentil cultivation in monoculture. The results of this study are also confirmed in our research, where the use of 1 row of buckwheat (S1) as a protective plant in soybean cultivation increased the height of the first soybean pod. Zhang and Li (Citation2003) found that both dominant and sub-species (wheat/maize, wheat/soybean, faba bean/maize, respectively) obtain higher yields in the intercropping than in their monoculture. The authors explain it as a stimulating effect of inter-species competition and the cooperation of species in collecting macro and microelements.
Increasing the yield and his quality in relay-strip intercropping system in our research can also be explained by the ‘border effect’. The superior performance in border plants is the better access to growth resources. The plants in relay-strip intercropping system have a better insolation and radiation use efficiency of the lower leaves than plants in a homogeneous canopy. The ratio of crop photosynthesis to total radiation intercepted in intercropping system may be higher than in the sole crops as a result of the more even distribution of radiation over the leaf layers (Mahallati et al. Citation2015; Gou et al. Citation2016; Van Oorta et al. Citation2020).
The results of our study prove that the fat and total protein content of soybeans was largely dependent on cultivar (). A large variation of these traits depending on the cultivar was also found by Pisulewska et al. (Citation1998) comparing seed yields and fat and fatty acid content in domestic soybean cultivars. The basic chemical composition of soybeans of both cultivars in this study was highly comparable with domestic soybean cultivars studied by Klebaniuk (Citation2007). The fat content of Annushka and Mavka soybeans noted in our study was lower than the fat content of soybeans in the study by Klebaniuk (Citation2007), while at the same time these contents were within the limits of the results found by Rani et al. (Citation2007). The content of amino acids in the seeds of individual soybean cultivars in our study was relatively strongly differentiated (). The greatest fluctuations occurred in the case of glutamic acid and histidine content. The lowest content of these amino acids was observed in seeds of Mavka cultivar and amounted to 51 mg/g for glutamic acid and 7.92 mg/g for histidine, in seeds of Annushka cultivar it was higher by 21.3% and 18.7%, respectively. According to Roche et al. (Citation2006), the composition of fatty acids changes depending on environmental conditions. An increase in temperature increases the content of oleic acid in the seeds of an oilseed plant. However, the oil content increased in conditions of good soil moisture and lower temperature. Our results showed a dominant share of omega-6 fatty acids, 52.85% for Mavka cultivar and 51.72% for Annushka cultivar, the content of omega-3 fatty acids was about 8% for both tested cultivars (), which is consistent with the literature data. According to Simopoulos (Citation2008), such a ratio of omega-6 to omega-3 acids is appropriate with dietary recommendations. This allows to conclude that intercropping simultaneously increases the content of desired fatty acids without disturbing their correct proportions. In Öner and Aykutlu (Citation2019) research considering all the properties (seed yield, protein and crude fat content, fatty acids composition) investigated and land equivalent ratio together, three rows of soybean intercropped with one row of maize were found to be the most appropriate intercropping system. This is probably due to the ratio of plant sizes (soybean and maize). It was found in the study by Kraska et al. (Citation2018), that intercropping significantly affects the quality parameters of legume seeds, including changes in the content of macro and microelements. The reasons for such changes can be found in the inter-species competition for the resources of elements in the soil occurring during the vegetation of plants.
The buckwheat is suitable intercrop for reducing pollen-mediated gene flow (PGF) from genetically modified (GM) cotton, and may be useful for reducing PGF from other insect-pollinated GM crops in the agricultural landscape, while simultaneously contributing to control of specific insect pests (Hemiptera: Aphididae, Aleyrodidae and Lygaeidae), likely due to attraction of their natural enemies (Yan et al. Citation2020). The described interactions could have contributed to increasing the quantity and quality of soybean yield in our research.
In our research, buckwheat reduced dry mass of weeds (average for both varieties) by 44.2% (S1) and 50.7% (S2) compared to monoculture of soybean (). In Sturm et al. (Citation2018) research buckwheat showed the highest allelopathic weed suppression with up to 28%. The research of these authors (Sturm et al. Citation2018) additionally shows that Stellaria media turned out to be the most sensitive weed against allelopathic effects induced by buckwheat. This weed species was not found in our research, even in soybean monoculture. In this study, it was found () that the most abundant weeds in soybean were Chenopodium album, Echinochloa crus-galli and Oxalis corniculata. The highest decrease in the number of weeds in soybean field with buckwheat occurred in the case of Oxalis corniculata (). Oxalis corniculata is a shade-loving species which confirms that the reduction in its number is the result of allelopathic properties of buckwheat. Findings by Cheriere et al. (Citation2020) also showed that the lowest weed infestation occurred in the intercropping with buckwheat, revealing a trade-off between soybean production and weed control. According to Kaczmarek (Citation2009), the rapid rate of initial growth and allelopathic action of common buckwheat on weeds reduces the occurrence of species such as Chenopodium album or Amaranthus retroflexus. Poggio (Citation2005) considers that the cultivation of several species at the same time may also reduce the diversity of weeds and lead to a change in the biomass composition between weed species. The increasing diversity of species composition of the community reduces its harmfulness to the crop. The influence of mixed cultivation on weed pressure is also described by Hauggaard-Nielsen and Jensen (Citation2005), although studies on the mechanisms responsible for this phenomenon are rare and ambiguous.
The results of Gawęda (Citation2007) show that the most common weed species in the soybean field were: Echinochloa crus-galli, Chenopodium album and Amaranthus retroflexus. This is confirmed to some extent in our study.
According to Mickiewicz and Mickiewicz (Citation2014), the perspective of development of organic farms in Poland will allow to reduce the consumption of harmful chemicals, while at the same time marketing food of higher pro-health value. The intercropping is an ideal way to facilitate production in both organic and integrated farms.
In summary, the studies showed that regardless of the soybean cultivar the most advantageous variant of relay-strip intercropping compared to the control in the form of cultivation in monoculture was sowing of soybean alternately with one row of buckwheat. The intercropping of soybean with two rows of buckwheat significantly reduced yielding. The intercropping had a positive effect on the chemical composition of the seeds of both soybean cultivar, except for the protein content, which was not significantly differentiated by the intercropping sowing method. The amino acid composition and the fatty acid profile of the seeds of this species were (with a few exceptions) the most favourable in facilities where soybeans were cultivated with two rows of buckwheat. This study also found that the soybean intercropping significantly reduced weed infestation for both tested soybean cultivars and sowing variants with buckwheat.
Acknowledgments
The authors would like to thank the owner of the farm for making the field available and for helping to conduct the field experiment.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Additional information
Funding
Notes on contributors
Wojciech Biszczak
Wojciech Biszczak is a PhD student at the Doctoral School “Production of food with increased pro-health values”, University of Life Sciences in Lublin. He conduct research on innovative plant cultivation systems. The research carried out mainly concerned plants of minor (chickpeas, buckwheat) and major (soybeans) economic importance, but with favorable health-promoting values in human and animal nutrition. Currently, He deal with the subject of relay-strip intercropping systems and the influence of this type of cultivation on the biophysical and health-promoting features of the obtained crop. His research focuses primarily on oilseeds and their physicochemical properties increasing the health benefits of the obtained vegetable oils.
Krzysztof Różyło
Krzysztof Różyło is a professor in the University of Life Sciences in Lublin where he has been a faculty member since 1999. His research interests lie in the area of the yielding parameters of crops, nutritional properties, health-promoting values and safety of plant origin food in the conditions of agronomic recycling of organic and mineral waste. Currently, His research evaluates the possibility of using elicitors in the increase of functional value of cereal grain under field conditions. In addition, he participates in a project concerning research on the composting of sewage sludge with biochar additives and the safety of their use in the recultivation of soil and fertilization of plants. as well as the use of nanoparticles in plant cultivation.
Piotr Kraska
Piotr Kraska is a profesor in the University of Life Sciences in Lublin where he has been a faculty member since 1997. He is the head of Subdepartment of Plant Ecology. In scientific research, he deals with the evaluation of the yield and quality of the crop in various ecological conditions; species biodiversity in agroecosystems; optimization of the technology of cultivation of cereals and oilseed flax, as well as lentils. Additionally, His research evaluates the possibility of using biochar in the cultivation of cereal crops and its impact on the physical, chemical and biological properties of the soil.
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