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Article

Comparative Analysis of Undersown Cover Crops and Bio-Preparations on Weed Spread and Organically Grown Spring Oilseed Rape Yield

by
Aušra Marcinkevičienė
1,*,
Arūnas Čmukas
1,
Rimantas Velička
1,
Robertas Kosteckas
2 and
Lina Skinulienė
1
1
Department of Agroecosystems and Soil Sciences, Agriculture Academy, Vytautas Magnus University, K. Donelaičio Str. 58, LT-44248 Kaunas, Lithuania
2
Department of Plant Biology and Food Sciences, Agriculture Academy, Vytautas Magnus University, K. Donelaičio Str. 58, LT-44248 Kaunas, Lithuania
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(18), 13594; https://doi.org/10.3390/su151813594
Submission received: 24 July 2023 / Revised: 2 September 2023 / Accepted: 7 September 2023 / Published: 12 September 2023
(This article belongs to the Section Sustainable Agriculture)
Browse Figures
Review Reports Versions Notes

Abstract

:
Undersown cover crops are an important tool for weed control in organic farming. The hypothesis of this research was that undersown crimson (incarnate) clover (Trifolium incarnatum Broth.), hairy (winter) vetch (Vicia villosa Roth.), perennial ryegrass (Lolium perenne L.), and winter rye (Secale cereale L.) in combination with bio-preparations inhibit the spread of weeds and influence the seed yield of spring oilseed rape in organic farming. The dry biomass of undersown cover crops, as well as the number and dry biomass of weeds, were determined before harvesting spring oilseed rape (Brassica napus L. spp. oleifera biennis Metzg.) (main crop) to identify the underlying influences on seed yield. We summarized that hairy vetch was distinguished by its rapid growth and by the fact that it produced an aboveground dry biomass that was significantly higher (1.9 to 12.4 times) compared with other cover crops, while crimson clover grown as a cover crop had a significantly higher aboveground dry biomass (by a factor of 3.2 to 4.9) compared with that of perennial ryegrass and winter rye. During the spring oilseed growing season, undersown cover crops did not suppress early emerging weeds that had not been controlled by inter-row loosening. During the spring growing season, weeds were best suppressed using bio-preparation-treated perennial ryegrass. The highest oilseed rape seed yield was obtained in 2020 after the application of bio-preparations in plots without any cover crops. Perennial ryegrass as a cover crop in combination with bio-preparations produced the highest reduction in oilseed rape seed yield. Further research should be directed toward determining the long-term effects of cover crops and bio-preparations on plant community formation in organic farming.

1. Introduction

Rapeseed is an important oilseed crop in Europe. However, its cultivation under organic farming conditions faces many challenges, such as variety selection, crop rotation selection, plant nutrition, water scarcity, weeds, diseases, and pests [1]. In Lithuania, in 2022, 6111.18 ha of oilseed rape was grown on organic farms, which included 829.66 ha of spring crop and 5281.52 ha of winter crop. In order to reduce the negative effects of anthropogenic activities, environmentally friendly solutions, such as improving crop rotation through cover cropping and growing crops for green manure, are being sought [2]. Recently, there has been a strong focus on sustainable agriculture, biodiversity, and maintaining environmental balance. One way to achieve this is through the cultivation of cover crops. Cover crops can be grown in a wide range of agricultural systems, but they play a major role in organic and sustainable farming systems [3]. Crops undersown amongst main crops provide dual benefits, not only as a cover crop that competes with weeds but also as a green manure that is incorporated into the soil, thereby becoming a fertilizer for the main crops [4,5]. The growth of cover crops is usually cut off before the sowing or planting of the main crop, but sometimes they are grown as undersown cover crops, i.e., the so-called ‘living mulch’ [6]. Although undersown cover crops are an alternative to herbicides, in addition to suppressing weeds, they can also suppress the main crop. To reduce competition between cover crops and main crops, it is preferable to sow cover crops among already growing main crops [7]. Cover crops can reduce the growth and yield of main crops under moisture-deficient conditions [8].
One of the main challenges in field crop management is weed control. Weeds are one of the most important agronomic problems in all farming systems, but the great threat and challenge in organic farming systems is that non-chemical weed control methods are less effective compared with herbicide use in intensive farming systems [9]. Sharma et al. [10] argued that crop diversification helps to reduce weed density by negatively affecting weed seed germination and weed growth. In organic farming systems, the inclusion of cover crops in crop rotations was shown by research to not only improve soil properties but also suppress weed growth [11]. Cover crops’ roots and residues release phytotoxic metabolites that help to compete with weeds [12,13]. The ability of cover crops to suppress weeds is often associated with their rapid emergence and their fast above- and belowground development [14,15]. Vincent-Caboud et al. [16] suggested that environmental conditions combined with agronomic decisions (sowing dates, genotype, etc.) influence the ability of cover crops to suppress weeds, regardless of the species grown. According to Schappert et al. [17], cover crops better aid in suppressing weeds when soil moisture conditions are optimal. Regression analysis shows that cover crop biomass determined resource uptake and weed suppression. Nitrogen availability early in the growing season and light availability later in the growing season have the greatest influence on weed biomass [18]. Interactions between the main and cover crop plant species reduce weed populations depending on climatic conditions [19]. According to Brust et al. [12], undersown cover crops reduce the density of dwarf weed species, while they do not significantly affect the density of tall weeds. Lorin et al. [20] argued that regardless of the growing conditions, undersown legume crops (field pea, berseem clover, common vetch, and a mixture of common vetch, faba bean, and berseem clover) reduce weed abundance in an oilseed rape crop by 20–75% compared with a rape crop without undersown plants. Verret et al. [21] reported that non-legume and legume cover crops reduce weed abundance in an oilseed rape crop by 52 and 38%, respectively. Research results by Khazaie et al. [22] show that Persian clover undersown (25, 50, 75, and 100% of the optimum sowing rate) into an oilseed rape crop significantly reduces weed density (63 to 91%) and aboveground dry matter biomass (35 to 75%).
In 2020, the European Commission started implementing the European Green Deal strategy. One of the programs of the green course—‘From the field to the table’—foresees a reduction in the amount of pesticides used by 50%, the amount of fertilizers by 20%, and the application of agro-ecological farmer practices by at least 25%, all by 2030 [23]. In the early 20th century, an increasing number of studies involving bio-preparations emerged during the rapid institutional expansion of agricultural research [24]. Bio-preparations are produced from natural organisms, substances derived from plants, and natural inorganic compounds; in addition, the process can control pest populations through a variety of methods [25,26]. This is a safer strategy for managing pest populations while also protecting human health and the environment [27]. Many types of bacteria, such as Bacillus thuringiensis and Bacillus popilliae; species of mushrooms (Beauveria bassiana, Verticillium lecanii, and Paecilomyces fumosoroseus); and viruses (Lymantria dispar, Neodiprion sertifer, etc.) can protect crops from the various diseases caused by pathogens. Bacillus gentis is one of the most widely used groups of microbes for the biological control of pathogens and pests. It was established that Bacillus spp. produce a wide variety of metabolites that can inhibit the growth and function of cellular organisms, such as bacteria; fungi; insects; nematodes; and noncellular organisms, such as viruses [28]. Hoarau et al. [29] established that bio-preparations are an alternative to conventional chemical insecticides and can affect the productivity of oilseed rape. The bio-preparations used increase the efficiency of plant nutrition and resistance to adverse environmental factors and improve the quality of production [30]. One of the reasons for the under-integration of biological control measures in cropping systems is the climatic fluctuations in open habitats, such as agroecosystems, where abiotic and biotic stressors can adversely affect the performance of biological control measures [31].
The shared hypothesis of these studies is that undersown cover crops in combination with bio-preparations inhibit the spread of weeds and influence the seed yield of spring oilseed rape under organic farming conditions.
Our aim was to determine the effect of undersown cover crops combined with the application of bio-preparations on weed infestation to assess how this affects the yield of spring rapeseed in organic farming.

2. Materials and Methods

2.1. Experimental Description

The field experiment was carried out in 2020–2022 at the Experimental Station of Vytautas Magnus University Agriculture Academy in Kaunas, Lithuania (54°53′ N latitude, 23°50′ E longitude) [32]. The soil of the experiment was Endocalcaric Amphistagnic Luvisol [33]. The soil agrochemical properties were as follows: pHKCl—6.51–6.92 and humus content—2.14–2.67%. The available plant nutrients in the soil were the following: P2O5—226–305 mg kg−1 and K2O—109–118 mg kg−1. Thus, the above-listed soil characteristics show that the topsoil richness in the organic carbon (OC) was low, but the available phosphorus (P2O5) that corresponded to group V was of particularly high content and the potassium (K2O) to group III was of average concentration according to the evaluation of the agrochemical properties of Lithuanian soil [34].

2.2. Experimental Design

A two-factor field experiment was set up using a split-plot design. The experimental treatments used were the following: factor A—bio-preparations (in subplots) ((1) not used (without BS) and (2) used (with BS)); factor B—undersown cover crops (in main plots) (Table 1).
Table 1. The experimental treatments used (Figure 1) [30].
Table 1. The experimental treatments used (Figure 1) [30].
The Experimental Treatments
No cover cropsNCC
Crimson (incarnate) clover—(Trifolium incarnatum Broth.) ‘Kardinal’ (10 kg ha−1 *)CC
Hairy (winter) vetch—(Vicia villosa Roth.) ‘Rea’ (50 kg ha−1 *)HV
Perennial ryegrass—(Lolium perenne L.) ‘Merkem’ (10 kg ha−1 *)PR
Winter rye—(Secale cereale L.) ‘Elias’ (50 kg ha−1 *)WR
* Recommendations of a.s. ‘Agrolitpa’.
In 2020 and 2021, the experimental field was cultivated twice with a germinator KLG-4.0 (Lithuania) and sown with spring oilseed rape (Brassica napus L. spp. oleifera biennis Metzg.) ‘Fenja’ (7 kg ha−1, 1.78 million sprout seeds per ha) (22 April 2020, 28 April 2021). The pre-crop was black fallow. The oilseed rape was sown with a 48 cm row spacing (sown every fourth row with 3 seed tubes closed in between). At the 2–3 leaf stage (BBCH 12–13), the inter-rows were loosened using a KOR-4.2-01 (Machinery Factory, Dnipras, Ukraine) soil loosener with arrow-type coulters. The loosened oilseed rape inter-rows were undersown with two-row cover crops at a 12 cm row spacing [32].
The fields where certified bio-preparations were applied were sprayed with ‘Recharge’ (which contains the following various bacteria and fungi: Bacillus subtilis, Bacillus megaterium, Bacillus polymyxa, Bacillus pumilus, Bacillus licheniformis, Bacillus cereus, Azospirillum, Paecilomyces lilacinus, Pseudomonas fluorescens, Trichoderma viride, Trichoderma harzianum, Metarhizium anisopliae, and Beauveria bassiana) (https://russellipm.com/product/recharge/) (accessed on 22 May 2023) and ‘Fizimite’ (a combination of surfactants and trace elements (Cu, 0.7%; Mn, 0.7%; and Zn, 0.7%)) (on https://russellipm.com/product/fizimite/) (accessed on 3 June 2023) while using an Amazone UF 901 sprayer (Amazone GmbH, Hasbergen, Germany). ‘Recharge’ protects plants from pests, nematodes, and diseases in a natural way. In addition, it increases plant nutrient absorption to boost growth and vigor. ‘Fizimite’ strengthens plants, as well as reliably increases their productivity, effectively washes away their surface from harmful organisms, and improves the plant defense system in a natural way; due to this, the plants can thus defend themselves against pests and diseases.
The bio-preparation ‘Recharge’ was sprayed 2 times: at sowing on the soil surface, and one month after sowing on the rape plants (1.5 kg ha−1). The bio-preparation ‘Fizimite’ was sprayed on the spring oilseed rape at the butonization stage (BBCH 57–59) (1.0 L ha−1).
The spring oilseed rape was harvested with a Wintersteiger Delta (Wintersteiger AG, Reid, Austria) combine harvester on 28 August 2020 and 3 September 2021. After the spring oilseed rape harvest, the cover crops were left to grow until the following spring. The cover crop was not additionally fertilized.
The initial plot area was 72 m2, and the plot area included in the recordings was 20 m2. The experiments were carried out with 4 replicates. The total number of experimental plots was 40.

2.3. Meteorological Conditions

The Lithuanian climate zone is a humid continental climate (Köppen–Geiger code: Dfb) [35].
In 2020, the plants resumed vegetation on 7 April. April was especially dry (Table 2). May was cold and wet. June was hot and humid. July was cooler and drier than normal. August was warmer than normal, and rainfall was close to the perennial normal. September was warm and dry. October, November, and December were warmer than normal, and rainfall was below the long-term normal. January and February 2021 were colder than normal.
In 2021, plant growth resumed on 11 April. April was colder and drier than normal (Table 2). May was cold and wet. June and July were hot and dry. August was cooler and wetter than normal. September and October were drier than normal. November and December were warmer than normal, and rainfall was close to the perennial normal.
In 2022, January and December were warmer, and March and April were colder than normal. March had almost no precipitation. Vegetation resumed on 9 April.

2.4. Research Methods

Soil agrochemical properties were determined before the initiation of the experiment according to conventional methods.
The aboveground biomass of the undersown cover crops was estimated at the end of the growing season and at the resumption of vegetation in spring. In each experimental plot, the aboveground biomass of the plants was divided into four randomly selected 0.25 m2 plots. Aboveground mass samples were dried at 105 °C in a drying oven, and the absolute dry biomass (Mg ha−1) was calculated.
The weediness of the spring oilseed rape crop was assessed before harvesting (BBCH 90–99) and after the resumption of crop vegetation in spring (April). In each plot, the aboveground weed biomass was divided into four randomly selected 0.25 m2 plots. The collected weed samples were dried in the laboratory. The number and dry biomass of each weed species were determined. The total number of weeds was converted into pcs. m−2 and the total dry biomass into g m−2.
The spring oilseed rape yield calculation was based on the standard 8.5% moisture and an absolutely clean seed content (Mg ha−1).

2.5. Statistical Analysis

The field data were analyzed using a two-way split-plot design. The means were separated using Fisher’s criterion and the least significant difference (LSD) test when the treatments and interactions were significant at p < 0.05 (at a 95% probability level) [36]. Statistical analysis of the data was performed using the package SELECTION [37]. The two-way ANOVA method was used to analyze the differences between the different factors, and these differences are marked by different letters. If normality assumptions were not met, the data were transformed using the mathematical function y = ln(x) prior to the statistical evaluation (number and biomass of weeds). Standard errors of the means are indicated by whiskers.

3. Results

3.1. Aboveground Dry Biomass of Cover Crops before Spring Oilseed Rape Harvest

In 2020, the largest aboveground dry biomass was associated with bio-preparation-treated hairy vetch (Figure 2). Crimson clover had a lower aboveground dry biomass compared with hairy vetch in both unsprayed and sprayed plots; however, no significant differences were found (p > 0.05). Perennial ryegrass and winter rye had significantly lower aboveground dry biomass compared with crimson clover and hairy vetch; more specifically, this was lower by a factor of 3.7 to 6.2 in the absence of bio-preparations, and by a factor of 4.4 to 6.3 with bio-preparation application, respectively (p < 0.05). All bio-preparation-treated cover crops produced higher aboveground dry biomass than untreated ones; however, no significant differences were found (p > 0.05).
In 2021, hairy vetch had the highest aboveground dry biomass of all the undersown crops (Figure 2). It had significantly higher aboveground dry biomass in unsprayed plots compared with the sprayed plots, ranging from 2.5 to 10.6 times higher. In addition, compared with the other undersown crops, it had significantly higher aboveground dry biomass in the sprayed plots, ranging from 2.6 to 14.4 times higher (p < 0.05). In plots with and without bio-preparation application, crimson clover produced significantly higher aboveground dry biomass compared with perennial ryegrass and winter rye (2.6 to 4.3 times and 3.2 to 5.5 times, respectively) (p < 0.05). Although perennial ryegrass had higher aboveground dry biomass than winter rye, no significant differences were found (p > 0.05).
The trials showed that the application of bio-preparations did not have any significant effect on the aboveground biomass of the undersown crops (p > 0.05), except in the hairy vetch plots (for which bio-preparations significantly increased the aboveground dry biomass by 35% (p < 0.05)).

3.2. Aboveground Dry Biomass of Cover Crops in Spring

Crimson clover was the worst performer in spring 2021 (Figure 3), with an aboveground dry biomass that was significantly lower (2.9 to 3.4 times) without bio-preparations, as well as 2.5 to 4.5 times lower with bio-preparations when compared with other plants cultivated as cover crops (p < 0.05).
The aboveground dry biomass of hairy vetch, perennial ryegrass, and winter rye was not significantly different between the untreated plots (p > 0.05). In the bio-preparation-treated plots, the aboveground dry biomass of the perennial ryegrass was found to be significantly higher (1.9 times higher) than that of the winter rye (p < 0.05). Bio-preparation application did not have any significant effect on the aboveground dry biomass of the spring-emerged cover crops (p > 0.05).
The aboveground dry biomass of the spring-emerged cover crops in 2022 was between 1.3 and 9.7 times higher than that in 2021. The aboveground dry biomass of the cover crops did not differ significantly between the plots that had no bio-preparation application (p > 0.05) (Figure 3). In the plots with bio-preparations, the aboveground dry biomass of crimson clover and perennial ryegrass was found to be significantly higher (2.1 and 2.0 times higher) than that of winter rye (p < 0.05). The aboveground dry biomass of spring-emerged cover crops in the bio-preparation-treated plots was not significantly different from their corresponding biomass in plots without bio-preparation application (p > 0.05).

3.3. Number and Dry Biomass of Weeds before Spring Oilseed Rape Harvest

In 2020, 25 weed species were found in the spring oilseed rape crop, including 17 annuals and 8 perennials. In 2021, 22 weed species were found, including 15 annuals and 7 perennials. The dominant annual dicotyledonous weed species were fat hen (Chenopodium album L.), scentless mayweed (Tripleurospermum perforatum (Merat) M. Lainz), and pale persicaria (Persicaria lapathifolia (L.) Gray) (Appendix A). The results show that the application of bio-preparations and undersown cover crops did not have any significant effect on the number of weeds in the spring oilseed rape crop (p > 0.05) (Figure 4). Regarding plots sprayed with bio-preparations, there was a downward trend in the number of weeds in spring oilseed rape plots without undersowing, as well as in the plots undersown with hairy vetch and perennial ryegrass, when compared with their corresponding unsprayed crops.
There was an increasing trend in weed numbers in the oilseed rape plots undersown with crimson clover, perennial ryegrass, and winter rye, as well as those sprayed with bio-preparations, when compared with the corresponding plots without bio-preparation treatment (Figure 4). The cause of such different results between years could be climatic conditions.
In 2020, the highest weed dry biomass was found in plots without cover crops or bio-preparation application (Figure 5). Undersowing, both with and without bio-preparations, tended to reduce weed dry biomass; however, no significant differences were found (p > 0.05). Spraying with bio-preparations enhanced the suppressive power of spring oilseed rape in plots without cover crops, as well as enhanced the suppressive power of both spring oilseed rape and cover crops in plots with undersown crimson clover and perennial ryegrass.
In 2021, the bio-preparations and cover crops did not have any significant effect on the dry biomass of weeds in the spring oilseed rape crop (p > 0.05) (Figure 5). In fact, spraying with bio-preparations tended to increase the weed dry biomass compared with unsprayed plots.

3.4. Number and Dry Biomass of Weeds in the Spring

In 2021, 9 weed species (4 annuals and 5 perennials) were found in the spring-emerged cover crops, and, in 2022, 13 weed species (9 annuals and 4 perennials) were found. The dominant weeds were scentless mayweed (Tripleurospermum perforatum (Merat) M. Lainz), annual meadow grass (Poa annua (L.)), and common dandelion (Taraxacum officinale F.H. Wigg.) (Appendix B).
In 2021, the number of weeds in plots with different cover crops (with and without bio-preparations) was not significantly different from that of plots without cover crops (p > 0.05) (Figure 6).
In 2022, the lowest number of weeds was found in the plot with perennial ryegrass grown as a cover crop (Figure 6) with the use of bio-preparations. However, no significant differences were found compared with other plots (p > 0.05). In the bio-preparation-treated plots without cover crops, as well as in plots with crimson clover, perennial ryegrass, and winter rye grown as cover crops, the number of weeds was found to be significantly lower (1.7 to 3.6 times) compared with the plot that was growing hairy vetch as a cover crop (p < 0.05). The number of weeds in the plot utilizing perennial ryegrass as a cover crop in combination with bio-preparations was found to be 2.1 times lower than in the plots without cover crops (p < 0.05). The use of bio-preparations, compared with no use, resulted in a significant 2.4-fold reduction in weed number in the plot utilizing crimson clover as a cover crop, and a significant 1.8-fold increase in weed number in the plot grown with hairy vetch (p < 0.05).
In 2021, the weed dry biomass was found to be significantly higher (1.8 to 5.2 times higher) in the plots sprayed with bio-preparations without cover crops compared with other analyzed plots (p < 0.05), except for the plot using hairy vetch as a cover crop in combination with bio-preparations (Figure 7). Without the use of bio-preparations, the weed dry biomass was not significantly different in both plots without cover crops and those with different cover crops (p > 0.05). The use of bio-preparations in the plot utilizing perennial ryegrass as a cover crop resulted in a significantly lower weed dry biomass (by a factor of 2.7 to 3.8) compared with those employing crimson clover, hairy vetch, and winter rye as cover crops (p < 0.05). This can be explained by the fact that perennial ryegrass overwinters well and can form high green biomass in springtime.
In 2022, the dry biomass of weeds in the analyzed plots was not significantly different without the use of bio-preparations (p > 0.05) (Figure 7). The use of bio-preparations in combination with perennial ryegrass and winter rye cover crops resulted in a significantly lower weed dry biomass compared with plots without cover crops (2.5 and 3.2 times lower) and the plot using hairy vetch as a cover crop (2.3 and 3.0 times lower) (p < 0.05). The weed dry biomass was found to be significantly lower (2.7 times) in the bio-preparation-treated sprayed plots when using winter rye as a cover crop than in the unsprayed plots (p < 0.05).

3.5. Spring Oilseed Rape Seed Yield

In 2020, the highest seed yield of spring oilseed rape was obtained with the use of bio-preparations and without the use of undersown cover crops (Figure 8). A significant 2.9-fold reduction in seed yield compared with the abovementioned crop was observed in the oilseed rape crop when using undersown perennial ryegrass as a cover crop in combination with the application of bio-preparations (p < 0.05). Crimson clover, perennial ryegrass, and winter rye undersowing in combination with bio-preparation-treated spraying resulted in a decrease in spring oilseed rape seed yield compared with the unsprayed crop; however, the measured differences were not significant (p > 0.05).
In May 2021, heavy rainfall formed a crust on the soil surface, which impaired the growth and development of the spring oilseed rape. The oilseed rape crop was sparse, and the conditions were favorable for weed growth. The spring oilseed rape seed yield was estimated to be between 1.7 and 6.3 times lower than that in 2020. In both bio-preparation-treated sprayed and unsprayed plots with hairy vetch (1.5 to 1.9 times) and perennial ryegrass (2.0 to 2.5 times), the seed yield was found to be significantly lower compared with plots without cover crops, as well as in those using undersown crimson clover and winter rye as cover crops (p < 0.05).

4. Discussion

Our study showed that in a spring oilseed rape crop, the highest aboveground dry cover crop biomass was observed for undersown hairy vetch; this result was influenced by the rapid growth of hairy vetch. Compared with other cover crops, the average aboveground dry biomass of hairy vetch was found to be significantly higher (1.9 to 7.7 times higher) in plots without biopesticides, as well as 1.8 to 12.4 times higher in plots with biopesticides. The aboveground dry biomass of crimson clover grown as a cover crop was found to be, on average, 3.2 to 4.9 times higher than that of perennial ryegrass and winter ryegrass in plots both with and without bio-preparations. The application of bio-preparations tended to increase the aboveground dry biomass of the cover crops. According to Brozović et al. [38], meteorological conditions influence the formation of winter cover crop biomass, and this varies between years. According to Arlauskienė and Maikštėnienė [39], under favorable meteorological conditions, cover crops accumulate between 3.34 and 5.78 Mg ha−1 of dry matter; conversely, they accumulate between 1.25 and 3.75 Mg ha−1 under less favorable conditions. The data found by Boselli et al. [40] indicate that winter rye (2.2 to 3.1 Mg ha−1) produced a higher aboveground biomass than hairy vetch (1.9 to 3.0 Mg ha−1). Vecchia et al. [41] reported that at 32 and 46 days after sowing, the aboveground biomass of rye was significantly higher than that of crimson clover and perennial ryegrass. Our data show that the aboveground dry biomass of spring-emerged cover crops was variable and dependent on wintering conditions (Table 1). On average, the highest aboveground dry biomass (0.78 Mg ha−1) was produced by perennial ryegrass sprayed with bio-preparations. This can be explained by the fact that perennial ryegrass overwinters well, and its outgrowth is better and faster compared with other cover crops. Bio-preparation application had little effect on the aboveground dry biomass of cover crops in spring. According to Toom et al. [42], hairy vetch and winter turnip rape produced higher aboveground biomass in the spring growing season compared with winter rye.
Weed competition with oilseed rape in the early stages of growth is particularly important. The critical period for weed control depends on factors such as weather conditions, weed population density, and dominant weeds [43]. In our study, we found that, during the spring oilseed-rape-growing season, the growth rate of cover crops was slow, and that cover crops did not suppress the early emerging weeds that had not been controlled by inter-row loosening. In addition, inter-row loosening may have encouraged the germination of new weed seeds. Bio-preparations had little effect on the spread of weeds. This result is consistent with the study of Salonen et al. [44]. A study by Sjursen et al. [45] showed that clover as a cover crop did not suppress short-lived weeds. In contrast, perennial ryegrass as a cover crop reduced weed biomass by 70% compared with plots without cover crops. Baraibar et al. [46] reported that in both autumn and spring growing seasons, weeds were better suppressed by the cover crops of the Poaceae family (cereal rye and oats) than those of the Fabaceae family (medium red clover and Austrian winter pea). Similar findings were reported by Kruidhof et al. [47]. The latter authors argued that winter oilseed rape and winter rye cover crops had a higher weed suppression ability than lucerne and white lupin during the autumn growing season.
The results of our study showed that the most favorable conditions for weed spread during the spring growing season were found in bio-preparation-treated plots without cover crops. The use of bio-preparations in combination with cover crops had a positive effect on weed suppression in spring. Weed control was the best in the bio-preparation-treated sprayed plots when using perennial ryegrass as a cover crop; compared with plots without cover crops, as well as other cover crops with and without bio-preparations, the average dry biomass of weeds was found to be between 1.8 and 3.8 times lower. In spring, the fast growth of cover crops can help to ensure low weed biomass, especially when cover crops are incorporated late in the season [48]. According to Restuccia et al. [49], a cover crop of subterranean clover significantly reduces weed biomass in spring. A study by Cornelius et al. [50] showed that the number of short-lived overwintering weed seedlings is reduced by 72% in a cover crop of winter rye. In other cover crops, the number of weed seedlings is reduced by 23 to 36%. Sjursen et al. [45] and Restuccia et al. [49] found a negative correlation between the aboveground biomass of cover crops and weed biomass. No such dependencies were found in our study.
Undersown cover crops compete with the main crops for nutrients, soil moisture, and light, thus leading to potential yield losses [51]. The results of our study showed that the spring oilseed rape seed yield depended on meteorological conditions and interspecific competition. In 2020, the highest seed yield was obtained with the application of bio-preparations and without cover cropping. Perennial ryegrass as a cover crop in combination with bio-preparations was the most important contributor to a reduction in rapeseed yield. In 2021, unfavorable meteorological conditions (Table 1) resulted in a low seed yield of 0.12 to 0.30 Mg ha−1. The highest yield losses were observed with undersown winter vetch and perennial ryegrass. The results from other authors’ studies show that non-legume cover crops reduce the yield of main crops by 3%, while legume cover crops increase yield by 6% [51]. Similar research results were reported by Verret et al. [21], stating that non-legume cover crops reduce rapeseed yield by 0.58 Mg ha−1, while faba bean cover crops increase the yield by 0.16 Mg ha−1. Bousselin et al. [52] also reported that legume cover crops do not significantly reduce the productivity of oilseed rape. Ahmad et al. [53] showed that bio-preparation use increases rapeseed yield by 13% compared with non-use.

5. Conclusions

Cover cropping and the use of bio-preparations are complex and especially important tools for weed management in organic farming. Hairy vetch was distinguished by its fast growth and by the fact that it produced an aboveground dry biomass that was significantly higher than that of the other cover crops. Crimson clover grown as a cover crop was found to have a significantly higher aboveground dry biomass than that of perennial ryegrass and winter rye. In the spring growing season, the highest aboveground dry biomass (0.78 Mg ha−1 on average) was produced by perennial ryegrass sprayed with bio-preparations. During the spring oilseed growing season, undersown cover crops did not suppress early emerging weeds that had not been controlled by inter-row loosening. During the spring growing season, weeds were best suppressed in the bio-preparation-treated plot using perennial ryegrass as a cover crop. The highest spring oilseed rape seed yield was obtained in 2020 after the application of bio-preparations in plots without any cover crops. Perennial ryegrass as a cover crop in combination with bio-preparations produced the highest reduction in oilseed rape seed yield. Bio-preparations are understudied, and further research is needed to evaluate them in different soil types and different climatic conditions.

Author Contributions

Conceptualization, methodology, software, validation, investigation, data curation, writing—original draft preparation, writing—review and editing, visualization, supervision, project administration, and funding acquisition: A.M., A.Č., R.K. and L.S.; resources and formal analysis: R.V. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

Appendix A

Table A1. Dominant weed species in the spring oilseed rape crop before harvest.
Table A1. Dominant weed species in the spring oilseed rape crop before harvest.
Weed SpeciesBio-Preparations
(Factor A)		Number of Weed (psc. m−2)/
Weed Dry Biomass (g m−2)
Undersown Cover Crops (Factor B)
WCCCCHVPRWR
2020
1. Chenopodium album L.−6.305.8010.47.1012.1
16.72.8015.36.5015.1
+4.607.905.804.207.50
10.114.32.601.305.30
2. Tripleurospermum perforatum
(Merat) M. Lainz		−0.801.702.501.302.10
0.400.304.702.002.30
+1.703.800.402.902.10
3.202.901.800.100.50
3. Persicaria lapathifolia (L.) Gray−30.027.536.331.726.7
71.452.062.047.640.6
+19.624.228.319.222.9
24.429.524.027.733.8
2021
1. Chenopodium album L.−8.757.258.502.508.75
81.152.131.425.561.4
+5.256.0011.83.759.50
45.734.641.925.559.4
2. Tripleurospermum perforatum
(Merat) M. Lainz		−4.506.253.757.007.25
21.442.723.649.035.0
+7.0010.04.004.758.00
74.645.141.124.030.2
3. Persicaria lapathifolia (L.) Gray−0.500.506.250.250
4.234.1530.80.180
+1.757.001.252.253.50
2.3829.913.59.709.53
Note: (−)—without bio-preparations and (+)—with bio-preparations. Undersown cover crops (factor B): WCC—without cover crop, CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye.

Appendix B

Table A2. Dominant weed species in the cover crops during the spring vegetation period.
Table A2. Dominant weed species in the cover crops during the spring vegetation period.
Weed SpeciesBio-Preparations
(Factor A)		Number of Weed (psc. m−2)/
Weed Dry Biomass (g m−2)
Undersown Cover Crops (Factor B)
WCCCCHVPRWR
2021
1. Tripleurospermum perforatum
(Merat) M. Lainz		−11.28.334.1710.89.17
19.122.214.017.812.7
+10.812.513.34.1712.1
19.823.227.51.5818.1
2. Poa annua L.−2.923.751.672.923.33
1.882.583.582.426.54
+10.02.085.830.832.50
22.11.967.920.380.62
3. Taraxacum officinale F.H. Wigg.−16.715.814,610.813,7
18.723.120.24.9224.2
+20.413.816.717.520.0
47.923.031.613.823.1
2022
1. Tripleurospermum perforatum
(Merat) M. Lainz		−1.6716.222.98.7511.2
5.5810.532.326.212.6
+18.36.2517.94.1710.4
32.18.628.334.218.04
2. Poa annua L.−2.0815.04.5814.212.1
5.2522.89.794.6216.8
+3.332.0814.20.834.17
3.673.5020.00.212.88
3. Taraxacum officinale F.H. Wigg.−22.13.753.331.672.08
33.42.9210.00.792.58
+2.922.084.584.171.25
5.882.791.888.252.67
Note: (−)—without bio-preparations and (+)—with bio-preparations. Undersown cover crops (factor B): WCC—without cover crop, CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye.

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Figure 1. Undersown cover crops: (a) CC; (b) HV; (c) PR; (d) WR.
Figure 1. Undersown cover crops: (a) CC; (b) HV; (c) PR; (d) WR.
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Figure 2. Aboveground dry biomass of cover crops before spring oilseed rape harvest. Note: BP—bio-preparations (factor A). Undersown cover crops (factor B): CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye. * and ** represent p < 0.05 and p < 0.01, respectively, and ns represents ‘not significant’. a–d Different letters indicate significant differences between the treatments (p < 0.05). The error bars indicate the standard error, where n = 4.
Figure 2. Aboveground dry biomass of cover crops before spring oilseed rape harvest. Note: BP—bio-preparations (factor A). Undersown cover crops (factor B): CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye. * and ** represent p < 0.05 and p < 0.01, respectively, and ns represents ‘not significant’. a–d Different letters indicate significant differences between the treatments (p < 0.05). The error bars indicate the standard error, where n = 4.
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Figure 3. Aboveground dry biomass of cover crops in the spring. Note: BP—bio-preparations (factor A). Undersown cover crops (factor B): CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye. * and ** represent p < 0.05 and p < 0.01, respectively, and ns represents ‘not significant’. a–c Different letters indicate significant differences between the treatments (p < 0.05). The error bars indicate the standard error, where n = 4.
Figure 3. Aboveground dry biomass of cover crops in the spring. Note: BP—bio-preparations (factor A). Undersown cover crops (factor B): CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye. * and ** represent p < 0.05 and p < 0.01, respectively, and ns represents ‘not significant’. a–c Different letters indicate significant differences between the treatments (p < 0.05). The error bars indicate the standard error, where n = 4.
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Figure 4. Number of weeds before spring oilseed rape harvest. Note: BP—bio-preparations (factor A). Undersown cover crops (factor B): CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye. ns represents ‘not significant’. Significant differences were not established (p > 0.05). Equal letters (a) indicate no differences. The error bars indicate the standard error, where n = 4.
Figure 4. Number of weeds before spring oilseed rape harvest. Note: BP—bio-preparations (factor A). Undersown cover crops (factor B): CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye. ns represents ‘not significant’. Significant differences were not established (p > 0.05). Equal letters (a) indicate no differences. The error bars indicate the standard error, where n = 4.
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Figure 5. Weed dry biomass before spring oilseed rape harvest. Note: BP—bio-preparations (factor A). Undersown cover crops (factor B): CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye. ns represents ‘not significant’. Significant differences were not established (p > 0.05). Equal letters (a) indicate no differences. The error bars indicate the standard error, where n = 4.
Figure 5. Weed dry biomass before spring oilseed rape harvest. Note: BP—bio-preparations (factor A). Undersown cover crops (factor B): CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye. ns represents ‘not significant’. Significant differences were not established (p > 0.05). Equal letters (a) indicate no differences. The error bars indicate the standard error, where n = 4.
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Figure 6. Number of weeds in the spring. Note: BP—bio-preparations (factor A). Undersown cover crops (factor B): CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye. * and ** represent p < 0.05 and p < 0.01, respectively, and ns represents ‘not significant’. a–d Different letters indicate significant differences between the treatments (p < 0.05). The error bars indicate the standard error, where n = 4.
Figure 6. Number of weeds in the spring. Note: BP—bio-preparations (factor A). Undersown cover crops (factor B): CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye. * and ** represent p < 0.05 and p < 0.01, respectively, and ns represents ‘not significant’. a–d Different letters indicate significant differences between the treatments (p < 0.05). The error bars indicate the standard error, where n = 4.
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Figure 7. Weed dry biomass in the spring. Note: BP—bio-preparations (factor A). Undersown cover crops (factor B): CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye. * and ** represent p < 0.05 and p < 0.01, respectively, and ns represents ‘not significant’. a–d Different letters indicate significant differences between the treatments (p < 0.05). The error bars indicate the standard error, where n = 4.
Figure 7. Weed dry biomass in the spring. Note: BP—bio-preparations (factor A). Undersown cover crops (factor B): CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye. * and ** represent p < 0.05 and p < 0.01, respectively, and ns represents ‘not significant’. a–d Different letters indicate significant differences between the treatments (p < 0.05). The error bars indicate the standard error, where n = 4.
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Figure 8. Spring oilseed rape seed yield. Note: BP—bio-preparations (factor A). Undersown cover crops (factor B): CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye. ** represents p < 0.01 and ns represents ‘not significant’. a–c Different letters indicate significant differences between the treatments (p < 0.05). The error bars indicate the standard error, where n = 4.
Figure 8. Spring oilseed rape seed yield. Note: BP—bio-preparations (factor A). Undersown cover crops (factor B): CC—crimson (incarnate) clover, HV—hairy (winter) vetch, PR—perennial ryegrass, and WR—winter rye. ** represents p < 0.01 and ns represents ‘not significant’. a–c Different letters indicate significant differences between the treatments (p < 0.05). The error bars indicate the standard error, where n = 4.
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Table 2. Meteorological conditions during the experimental period (Kaunas Weather Station).
Table 2. Meteorological conditions during the experimental period (Kaunas Weather Station).
Year/MonthJanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecember
Average air temperature (°C)
20202.52.23.66.910.519.017.418.714.910.35.20.6
2021−3.5−5.01.76.211.419.522.616.511.68.14.2−2.3
20220.021.41.76.211.017.717.920.911.110.22.9−2.5
Long-term average−3.7−4.70.36.913.216.118.717.312.66.82.8−2.8
Precipitation rate (mm)
202052.854.929.34.094.499.360.492.813.352.530.017.1
202182.212.322.033.7121.640.348.4122.229.127.255.538.0
202269.073.73.6038.484.077.6100.538.726.017.730.744.1
Long-term average38.135.137.241.361.776.996.688.960.051.051.041.9
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MDPI and ACS Style

Marcinkevičienė, A.; Čmukas, A.; Velička, R.; Kosteckas, R.; Skinulienė, L. Comparative Analysis of Undersown Cover Crops and Bio-Preparations on Weed Spread and Organically Grown Spring Oilseed Rape Yield. Sustainability 2023, 15, 13594. https://doi.org/10.3390/su151813594

AMA Style

Marcinkevičienė A, Čmukas A, Velička R, Kosteckas R, Skinulienė L. Comparative Analysis of Undersown Cover Crops and Bio-Preparations on Weed Spread and Organically Grown Spring Oilseed Rape Yield. Sustainability. 2023; 15(18):13594. https://doi.org/10.3390/su151813594

Chicago/Turabian Style

Marcinkevičienė, Aušra, Arūnas Čmukas, Rimantas Velička, Robertas Kosteckas, and Lina Skinulienė. 2023. "Comparative Analysis of Undersown Cover Crops and Bio-Preparations on Weed Spread and Organically Grown Spring Oilseed Rape Yield" Sustainability 15, no. 18: 13594. https://doi.org/10.3390/su151813594

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