False Seedbed for Agroecological Weed Management in Forage Cereal–Legume Intercrops and Monocultures in Greece

Abstract

Intercropping cereals with legumes is a widely used agronomic practice to improve forage yield and quality in forage cropping systems. The main objective of the present study was to investigate the potential of a false seedbed to reduce weed pressure in intercrops and monocultures of annual ryegrass and berseem clover during the 2020–2021 and 2021–2022 growing seasons in western Greece. A split-plot randomized complete block design with four replications was set up. Seedbed manipulations assigned to the main plots included: normal seedbed preparation (NSB) and seeding, and two different false seedbeds. In the first (FSB 1) and second false seedbeds (FSB 2), weeds were controlled by shallow tillage at 1 and 2 weeks, respectively, after the first tillage and immediately before crop sowing. Forages were subplots of berseem clover (BCM) and annual ryegrass monocultures (ARM) and three intercrops with BCM:ARM ratios of 75:25 (ARBC 1), 50:50 (ARBC 2), and 25:75 (ARBC 3). FSB 1 reduced weed biomass by 27% and 34% compared to NSB in 2020–2021 and 2021–2022, respectively (p ≤ 0.001). FSB 2 improved forage yield by 9% and 14% in 2020–2021 and 2021–2022, respectively, compared to FSB 1. Compared to NSB, FSB 2 also increased forage yield by 11% in 2020–2021 and 17% in 2021–2022. Berseem clover biomass was higher in FSB 2 than in NSB main plots in both years. In the first harvest, ARBC 3 was the most weed-suppressive intercrop, which also provided the highest forage yield in both the first and second harvests of both years, followed by ARM and ARBC 2. In the second harvest, forage yield was 11% and 12% higher in ARBC 3 subplots than in ARBC 1 and BCM subplots, respectively. Similar results were obtained for cumulative forage yield from two harvests. Further research is needed to evaluate other alternative practices for agroecological weed management in low-input forage production systems in the Mediterranean region.

1. Introduction

Intercropping is the joint cultivation of two or more crops in the same field over a period of time [1]. In forage production, intercropping of annual winter cereals and legumes is widely used to support sustainable forage production in low-input farming systems in the Mediterranean region [2,3,4]. Among the numerous forage crops that can be used for this purpose, annual ryegrass (Lolium multiflorum Lam.) and berseem clover (Trifolium alexandrinum L.) intercrops have shown great potential to produce high forage yields with excellent forage quality under Mediterranean soil and climatic conditions [5,6,7,8,9].

Cereal–legume intercrops have numerous advantages compared to cereal and legume monocultures [4]. In particular, cereal monocultures produce large amounts of forage biomass but with lower protein content and nutritional value; legume monocultures are associated with the risk of causing bloat and bone abnormalities in animals due to the unbalanced ratio of P and Ca, and are generally less productive than cereals [2,10]. In contrast, cereal–legume combinations are optimal because cereals ensure high forage yields, improve light absorption, and facilitate mechanical harvesting, while legumes improve protein content and overall forage quality compared to cereal monocultures [11]. From an agronomic perspective, intercropping species with different resource requirements and functional capabilities, as in the case of cereal–legume intercrops, leads to complementarity in resource utilization, suggesting that intercrops have better overall resource utilization than the individual species grown as monocultures [12]. This often results in higher biomass production and may also improve weed suppression because intercrops utilize a wider range of nutrients that are less available to weeds [13,14,15]. To improve weed suppression, it is critical to choose the right seed ratio of each species in the intercrop. Cereals tend to grow more aggressively than legumes, and seeding rates of both species in the mix should be carefully balanced not only to form an intercrop that competes well with weeds and provides high forage yields, but also to avoid unacceptable levels of interspecific competition between the cultivated species [16].

In any case, weed competition can be a major obstacle limiting forage yield and degrading forage quality in both intercrops and monocultures [17,18,19,20]. Therefore, it is important to develop weed management practices to reduce weed pressure on forage crops. Emphasis should be placed on non-chemical, cultural practices that support the concept of low-input forage production systems [21]. One of these cultural practices for agroecological weed management is the preparation of a false seedbed. A false seedbed is formed when the field is prepared for sowing and weeds are allowed to germinate after the initial tillage operations [22]. It should be noted here that under drier conditions, a light sprinkler irrigation after initial tillage is necessary to stimulate weed emergence [23]. After weed seedlings emerge, they are controlled by very shallow tillage (to a soil depth of 10 cm) and then the crop is sown in a less competitive environment that has a significant competitive advantage over later emerging weed cohorts [24]. False seedbeds have been shown to result in significantly lower weed biomass compared to conventional seedbed preparation in cereals and legumes [23,24]. In forage crops, recent studies have shown that a false seedbed can actually reduce weed pressure to some extent, especially when combined with increased crop populations and crop diversification practices [25]. One research gap in the implementation of this cultural practice is the optimal period between initial tillage operations and weed control before crop sowing. This period can vary from crop to crop and depends on the specific soil and climatic conditions of each agricultural area [26].

The main objective of the present study was to investigate the potential of a false seedbed to reduce weed pressure in annual ryegrass–berseem clover intercrops and monocultures grown for forage production. Our hypothesis was that increasing the days until sowing from one to two weeks after the first tillage would increase the number of emerged weed seedlings when a false seedbed is prepared. Therefore, these emergent seedlings would later be uprooted by shallow tillage immediately prior to sowing, resulting in lower weed densities at later crop growth stages. We also compared annual ryegrass and berseem clover intercrops and monocultures for their ability to suppress weeds and their potential for forage yields. We hypothesized that increasing the ratio of annual ryegrass to berseem clover would improve weed suppression due to the rigorous growth of annual ryegrass. In such a mixed crop, where berseem clover is still present but at a lower ratio, we also wanted to investigate whether berseem clover is being smothered by the aggressive growth of annual ryegrass or whether it is still producing sufficient amounts of biomass to contribute to overall forage production and quality. Forage quality data are not included in this paper because we first want to present detailed agronomic information on the effects of the above cultural practices (false seedbed and intercropping) on weed density, while providing data on weed species level, forage quality, and legume biomass production. Forage quality will be the main research objective of our future work (following current work).

2. Materials and Methods

2.1. Site Description

A two-year field trial was conducted from 2020 to 2022 (i.e., during the 2020–2021 and 2021–2022 growing seasons) in the Vonitsa region of western Greece (20°53′54″ east latitude (E), 38°53′38″ north longitude (N)). The World Geodetic System 1984 (WGS84) geographic coordinate system was used to collect accurate site data. The soil type was a clay loam whose physicochemical properties (0 to 15 cm soil depth) were 29.6% clay, 33.7% silt, and 36.7% sand, with a pH of 7.4, an organic matter content of 1.24%, and 81 ppm total nitrogen. Regarding climatic conditions, the average monthly air temperature in 2020–2021 was slightly higher in the period from October 2020 to March 2021 than in the corresponding period in 2021–2022. Monthly precipitation was significantly higher in all months from October to February in 2021–2022 than in 2020–2021. However, higher precipitation heights fell in April and May 2021 than in April and May 2022 (

Table 1. Mean monthly temperature (°C) and total monthly precipitation (mm) observed in the experimental area during 2020–2021 and 2021–2022 growing seasons.

Month	Mean Temperature (°C)		Total Precipitation (mm)
	2020–2021	2021–2022	2020–2021	2021–2022
October	21.2	18.8	16.6	120.1
November	19.2	16.4	2.4	66.4
December	14.4	12.5	79.9	43.3
January	12.5	9.2	33.8	63.6
February	12.3	11.8	38.2	21.5
March	13.0	10.1	57.5	18.8
April	16.7	17.4	34.7	3.1
May	22.7	22.3	9.0	3.8
June	26.0	27.3	6.1	4.4

).

The predominant winter weeds that occurred during the fallow period in previous years were sterile oat (Avena sterilis L.) and wild mustard (Sinapis arvensis L.). Sterile oat (2n = 42) is a stout annual grass with large leaves that resembles cultivated oats in general appearance, is self-pollinated, and is well established in Mediterranean countries [27]. It is the most widespread and noxious weed in winter cereals in Greece, significantly reducing crop yields and contaminating commercial seed, while its presence in the field also limits the yield of legumes [24,28,29]. It is worth mentioning that plants usually produce 5 or more tillers plant⁻¹, resulting in a high number of stems per unit area [29]. In crop–weed interference studies, the presence of 110 sterile oat stems m⁻² reduced the grain yield of wheat and triticale by 61%, while the reduction in grain yield of barley was 9% [30]. Its seeds can remain dormant in the soil for up to 5 years; germination temperature ranges from a minimum of 2 °C to a maximum of 30 °C, with an optimum of 10 °C [31]. Seed germination is higher under a photoperiod than under constant darkness in incubation [32]. Reproduction is by seed only; seeds usually emerge from soil depths of 2 and 5 cm, and especially when rainfall exceeds 10 mm [33].

Wild mustard (2n = 18) is a self-incompatible, insect-pollinated, annual, winter dicotyledonous weed of the Brassicaceae family that frequently infests winter field crops in Greece [24,28]. According to recent experiments conducted in Greek winter wheat fields, it is a very competitive weed species. Its presence in the field at a density of 22 plants m⁻², together with other broadleaf weeds, can lead to yield reductions of up to 43% if no weed control measures are taken [34]. The occurrence of this weed is similar to that of other small-seed broadleaf weeds and requires some seed exposure to light and adequate soil moisture (70% of field capacity) [35]. Propagation is by seed only; seeds germinate at temperatures ranging from 1.5 °C to 48 °C, with 20 °C considered the most suitable temperature for radicle germination [36]. Seeds usually have a dormancy period of 2 years, but older studies report that they can remain viable in soil for up to 60 years [35]. In the most recent study by Singh et al. [36], emergence was highest, i.e., 52%, at a burial depth of 1 cm, and 29%, 46%, and 23% at the surface and at 2- and 4-cm depths, respectively.

Both weeds became dominant due to the crop rotation implemented at this site during the last 10 years. Specifically, alfalfa (Medicago sativa L.) was grown for three years and silage maize (Zea mays L.) for four years. The field was kept fallow for one year and then silage maize was grown for two additional years (all crops were grown using conventional tillage methods). During all winter periods, the field was fallow and both of the above weed species were able to grow uncontrolled and subsequently establish a large seed bank because of their high seed production under non-competitive conditions. As an example of seed production of sterile oat, Mahajan and Chauhan [33] reported the production of about 2500 seeds per plant in the absence of competition [33]. Wild mustard is another species that is considered a prolific seed producer, as it can produce up to 3500 seeds per plant under non-competitive conditions [37].

2.2. Experimental Setup and Design

Annual ryegrass and berseem clover were the forage crops grown as monocultures and also in mixtures. Certo and Maremma (Mediterranea Sementi Srl, Teramo, Italy) were the annual ryegrass and berseem clover cultivars used, respectively. Both cultivars were selected primarily for their resistance to adverse climatic conditions, resistance to fungal attack, high yield potential, and forage quality. Certo is an annual ryegrass cultivar with medium earliness suitable for intercropping cereal–legume forages. This is due to its lower plant height and less aggressive growth compared to other commercial varieties, so it does not suppress legume growth in mixed crops (Kanatas, personal communication). In addition, Maremma is a medium-earliness berseem variety characterized by fast growth, an upright growth habit, and great plant height, making it adequately competitive in intercropping with annual grasses. According to the seed supplier, this cultivar is ideal for mixtures with annual ryegrass and tall fescue (Festuca arundinacea Schreb.), with the seed ratio of a berseem clover:annual ryegrass:tall fescue set at 30:50:20. In summary, we used cultivars with the appropriate characteristics to ensure that berseem clover in intercrops would not be smothered by annual ryegrass, which generally exhibits more rapid growth. Soil was plowed to a depth of 30 cm on 18 October 2020, and 20 October 2021, and plowed with a disk harrow (two passes to a depth of 20 cm) on 2 November 2020, and 4 November 2021, to break up soil clods and create a firm seedbed. The field was not fertilized neither at this time nor after the first harvest where regrowth was stimulated by irrigation, as described in Section 2.3.

Sowing dates were different depending on the different seedbed manipulations included in the experimental design. The experiment was conducted in a two-factor randomized block design (split plot) with four replicates (blocks). Three seedbed manipulations were assigned to the main plots. Five different forages, consisting of three annual ryegrass and berseem clover intercrops and two monocultures of both species, were assigned to the subplots. The size of the subplot was 12 m² (3 m long and 4 m wide), and the size of the main plot was 240 m² (15 m long and 16 m wide). Since each subplot was replicated 4 times, this resulted in 60 subplots; the total experimental area was 720 m². Weed–free 0.4 m wide borders were maintained between adjacent subplots. In 2021–2022, i.e., the replication year, new plots (main plots and subplots) were established in new areas of the site to actually replicate the experiment over time and avoid the cumulative effect of treatments on the parameters studied.

Seedbed manipulations initially included the normal seedbed manipulation, where seeding was done immediately the day after seedbed preparation. Two different false seedbeds were also prepared. In the first false seedbed, weeds were allowed to emerge for approximately 1 week before being controlled with shallow tillage (10 November 2020 and 11 November 2021). In the second false seedbed, weeds were allowed to emerge for approximately 2 weeks before being controlled with shallow tillage (18 November 2020 and 19 November 2020). In both false seedbeds, shallow tillage was performed with hand hoes to a very shallow depth of 3–5 cm to uproot emerging weed seedlings. The reason for choosing this equipment is the observation that when a disk harrow was used, even when set as shallow as possible, the 5 cm soil depth limit was still exceeded. However, in false seedbeds, the depth of the last shallow tillage before sowing must be between 3–5 cm and must not exceed the limit of 5 cm soil depth. If the tillage depth exceeds this limit, the tillage will stir up non-dormant weed seeds in the upper soil layers, which will germinate and destroy the resulting false seedbed [22,26]. Therefore, we decided to use hand hoes, where the tillage depth can be manually controlled by the workers, so that the tillage is done very carefully and at a very shallow depth. At this point, it should be noted that irrigation of the soil was not necessary, since the tillage was carried out before light rains, which typically occur in western Greece in early October. In the following, the normal seedbed tillage, the first false seedbed and the second false seedbed will be abbreviated as ‘NSB’, ‘FSB 1’ and ‘FSB 2’, respectively.

Immediately after weed control by shallow tillage, crops were sown in rows 20 cm apart using a ‘SJ Expert’ hand seeder (Sepeba Ebra, Les Grès, Saint-Martin-du-Fouilloux, France). Seeding rates were adjusted to achieve the following ratios of berseem clover:annual ryegrass: 100:0, 75:25, 50:50, 25:75, and 0:100. A seeding rate of 30 kg seed ha⁻¹ was used for both monocultures. This seeding rate is the maximum recommended in Greece for berseem clover and the minimum one recommended for annual ryegrass. The thousand grain weights of annual ryegrass and berseem clover were 3.2 and 3.5 g, respectively. For the intercrops, the seeding rates were adjusted to correspond to the above proportions and the total seeding rate of 30 kg ha⁻¹ was maintained. In the first intercrop, the seeding rates of berseem clover and annual ryegrass were 22.5 kg ha⁻¹ and 7.5 kg ha⁻¹, respectively. In the second intercrop, the seeding rate was 15 kg ha⁻¹ for both species. In the third intercrop, the seeding rate of berseem clover was 7.5 kg ha⁻¹, while the seeding rate of annual ryegrass was 22.5 kg ha⁻¹. For all forage crops (intercrops and monocultures), the sowing depth was 2 cm. It should also be noted that for the intercrops, we performed a mixed intercropping in which the seed of each species was sown in the same row. In the following, berseem clover and annual ryegrass as monocultures are abbreviated as ‘BCM’ and ‘ARM’, respectively. The first, second, and third intercrops are abbreviated as ARBC 1, ARBC 2, and ARBC 3, respectively.

2.3. Data Collection

Weed density was evaluated once in each subplot when the annual ryegrass plants were about mid-tillering stage (BBCH 25) and the berseem clover plants had formed 2–3 side shoots 0.5 cm long (BBCH 22–23). The exact dates on which weed density was assessed were 18 December 2021 and 21 December 2022. To collect weed data, three metal 0.5 m² quadrats were permanently placed in each subplot and marked with 1 m high wooden stakes in areas with uniform weed flora and away from subplot edges. In each quadrat, weeds were harvested by hand and separated by species. Weed counts were made to estimate the density of each species, including species that occurred at minor densities in the experimental field (1–3 plants m⁻²). The densities of sterile oat and wild mustard are the data reported on species level. To calculate the total weed density per unit area, the densities of the minor weeds in each quadrat were added to the densities of the predominant weeds.

All forages were first harvested manually at a stubble height of 5 cm in each subplot from three sampling points determined by a wooden 1 m² quadrat. The first harvest occurred on 24 April 2021, and 29 April 2022, when berseem clover plants were in the early flowering stage (BBCH 65). Samples were separated into annual ryegrass, berseem clover, and weeds, and placed in numbered plastic bags. Each fraction from each quadrat was oven dried (DHG–9025, Knowledge Research S.A., Athens, Greece) at 60 °C for 48 h to measure the dry biomass of annual ryegrass, berseem clover, and weeds using a digital balance ‘KF–H2’ (Zenith S.A., Athens, Greece). To estimate forage yield in each subplot, the sums of biomasses of annual ryegrass and berseem clover were calculated. To encourage regrowth, a sprinkler irrigation was applied after mowing and another one after two weeks throughout the field. In the meantime, before the two irrigations, a foliar application of completely water-soluble urea (N–P–K: 46–0–0; AGRI.FE.M. Ltd., Athens, Aspropirgos, Greece) was also carried out. Urea was applied at a concentration of 0.87% (v/w) with a pressurized Gloria^® 410 T sprayer (Gloria Haus & Gartengeraete GMBH, Witten, Germany) calibrated to deliver 200 L ha⁻¹ of spray solution at a constant pressure of 300 kPa through a brass hollow-cone nozzle (2 mm diameter; 80° spray angle) to provide 40 kg N ha⁻¹ to the crop. In early summer (10 June 2021 and 14 June 2022), all forages were harvested a second time, and forage yield, berseem clover biomass, and weed biomass were again evaluated using the same procedures as the first harvest. Cumulative forage yield and berseem clover biomass from two harvests were also calculated.

2.4. Statistical Analysis

All data were first subjected to a three-way ANOVA, with years, seedbeds, and forages as fixed effects and blocks (replicates) as random effects. If the effects of years were significant or significant interactions were found between year and seedbed or year and forage, the data were reanalyzed separately for each year. If year effects were not significant or significant interactions between year and seedbed or year and forage were not detected, data were pooled across years and reanalyzed. For either the data analyzed for each year or the pooled data across years, all secondary analyses were conducted using two-way ANOVA (seedbed by forage), with seedbed and forage considered fixed effects and blocks considered random effects. All analyses were conducted at a significance level of a = 0.05, and means were separated using Fisher’s least significance difference (LSD) test.

We also plotted the relationships between (a) total weed density and days until sowing in the false-bed main plots (FSB 1 and FSB 2) and (b) forage yield and days until sowing in the FSB 1 and FSB 2 main plots using the second-degree polynomial model:

y = ax² + bx + c

(1)

where c is the intercept, a and b are constant coefficients, y is the dependent variable representing total weed density or forage yield, and x is the dependent variable representing days until sowing in FSB 1 and FSB 2 main plots. To perform the above polynomial regressions, data from each intercrop in each year were analyzed separately. Statgraphics Centurion XVI (Statgraphics Technologies, Inc., P.O. Box 134, The Plains, VA, USA) was the statistical package used in all analyses (including all ANOVAs and polynomial regressions).

3. Results

3.1. Weed Density

Sterile oat and wild mustard were the predominant weed species in both experimental years. Sterile oat density was significantly influenced by years (p ≤ 0.05), interaction of year and seedbed (p ≤ 0.05), and the forage factor as well (p ≤ 0.001). In addition, years (p ≤ 0.05), seedbed (p ≤ 0.001), and forage (p ≤ 0.01) affected the density of wild mustard. Total weed density was influenced by year–seedbed (p ≤ 0.001) and seedbed–forage interactions (p ≤ 0.05; Table S1). Sterile oat density was 38% higher in 2021–2022 compared to 2020–2021, and wild mustard increased 28% in 2021–2022 compared to 2020–2021. Total weed density was also 32% higher in the second growing season than in the first growing season (Figure 1a–c).

Seedbed affected sterile oat density in 2020–2021 (p ≤ 0.001) and 2021–2022 (p ≤ 0.01). Wild mustard density and total weed density were also influenced by the seedbed factor in both years. Forage affected sterile oat density and total weed density in both growing seasons (p ≤ 0.001). The same was true for wild mustard density in 2021–2022 (p ≤ 0.01), as opposed to 2020–2021. A significant interaction between seedbed and forage was found for total weed density in the second growing season (

Table 2. Overall statistical analyses of degrees of freedom (for seedbed factor; for forage factor; for seedbed and forage interaction; for the error) and of the significance of effect (seedbed; forage; seedbed and forage interaction and tests performed) on sterile oat density, wild mustard density, and total weed density. Data are presented separately for the two growing seasons (2020–2021 and 2021–2022).

Factors	DF 1	Sterile Oat		Wild Mustard		Total Weeds
		2020–2021	2021–2022	2020–2021	2021–2022	2020–2021	2021–2022
Seedbed (S)	2	0.0004	0.0012	0.0002	0.0005	0.0000	0.0001
Error (a) 2	6
Forage (F)	4	0.0000	0.0002	0.0823	0.0075	0.0000	0.0000
S × F	8	0.2612	0.2420	0.5134	0.3660	0.4324	0.0325
Error (b) 3	36
Total	59

¹ DF: degrees of freedom; ² Error (a): S × Block; ³ Error (b): F(S) × Block.

).

Sterile oat density was lowest in FSB 2 main plots, medium in FSB 1 main plots, and lowest in NSB main plots in both 2020–2021 and 2021–2022. Similar observations were made for wild mustard density. In 2020–2021, total weed density was 18% and 81% lower in FSB 2 plots compared to FSB 1 and NSB, respectively. FSB 1 also reduced weed density compared to NSB. Similar results were obtained in 2021–2022 (

Table 3. Sterile oat density (no. m⁻²), wild mustard density (no. m⁻²), and total weed density (no. m⁻²) in 2020–2021 and 2021–2022 (“nο.” is the abbreviation of “number”).

Factors	Sterile Oat (no. m−2)		Wild Mustard (no. m−2)		Total Weeds (no. m−2)
	2020–2021	2021–2022	2020–2021	2021–2022	2020–2021	2021–2022
Seedbed
NSB 1	16.8 a 2 (3.2)	31.2 a (4.2)	16.6 a (3.8)	23.1 a (3.7)	35.0 a (5.4)	55.6 a (5.6)
FSB 1	15.4 a (2.5)	20.1 b (4.8)	11.8 b (2.8)	16.1 b (3.3)	28.6 b (3.3)	37.6 b (4.7)
FSB 2	3.3 b (1.8)	5.9 c (2.7)	2.7 c (1.2)	4.4 c (1.7)	6.5 c (1.5)	11.1 c (2.8)
LSD0.05	4.1	8.8	3.5	5.6	3.2	9.3
Forage
BCM	19.3 a (2.9)	27.5 a (5.7)	14.0 a (4.3)	18.2 a (3.0)	34.8 a (3.6)	46.9 a (6.3)
ARBC 1	17.4 a (2.2)	25.1 a (4.1)	10.6 ab (2.7)	19.1 a (2.8)	29.1 ab (3.7)	45.5 a (2.9)
ARBC 2	9.3 b (3.8)	16.2 b (4.2)	11.7 ab (2.1)	12.0 b (2.5)	22.0 bc (4.9)	29.3 b (5.5)
ARBC 3	7.3 b (2.3)	13.7 b (2.6)	6.6 b (1.5)	11.4 b (2.1)	15.0 c (2.9)	26.0 b (2.5)
ARM	5.8 b (1.2)	12.8 b (2.8)	8.8 ab (2.3)	11.8 b (3.1)	15.6 c (2.1)	26.0 b (4.6)
LSD0.05	4.8	7.2	5.4	5.3	7.1	8.1

¹ NSB: Normal seedbed, FSB 1: First false seedbed, FSB 2: Second false seedbed, BCM: Berseem clover monoculture, ARBC 1: First intercrop with annual ryegrass and berseem clover in a 25:75 ratio, ARBC 2: Second intercrop with annual ryegrass and berseem clover in a 50:50 ratio, ARBC 3: Third intercrop with annual ryegrass and berseem clover in a 75:25 ratio, ARM: Annual ryegrass monoculture (see text in Section 2.2 for details); ² Numbers followed by the same letter in the same column are not significantly different.

).

Sterile oat density was significantly lower in both 2020–2021 and 2021–2022 in subplots ARBC 2, ARBC 3, and ARM, than in subplots BCM and ARBC 1. In 2020–2021, ARBC 3 had the lowest wild mustard density. Wild mustard density was highest in the BCM subplots. Intermediate values corresponded to ARBC 1, ARBC 2, and ARM. In 2021–2022, ARBC 2, ARM, and ARBC 3 suppressed wild mustard density compared to ARBC 1 and BCM. Total weed density decreased by 48% and 56% in 2020–2021 in ARBC 3 compared to ARBC 1 and BCM, respectively. In 2021–2022, ARM and ARBC 3 suppressed total weed density by 42% and 44% compared to ARBC 1 and BCM, respectively. In addition, ARBC 2 did not differ from ARBC 2 and ARBC 3.

As the number of days before sowing increased from FSB 1 to FSB 2 compared to NSB, the total weed density decreased, as indicated by the strong second-degree polynomial relationships between total weed density and days until sowing. This was observed for all forages in both experimental years (Figure 2a,b).

In 2020–2021, approximately 78% of the variation in total weed density in the BCM and ARBC 1 subplots was due to the days elapsed until sowing. The coefficient of determination (R–squared; R²) was lower in subplots ARBC 2 (R² = 0.5161) and ARBC 3 (R² = 0.6780), but higher in subplots ARM (R² = 0.8628). In 2021–2022, the correlation between the dependent (total weed density) and independent variables (days until sowing) was weaker in subplots BCM (R² = 0.5603) and ARM (R² = 0.7128), but stronger in subplots ARBC 2 (R² = 0.7249). The highest R² values were found in subplots ARBC 3 (R² = 0.9239) and ARBC 1 (R² = 0.9467). An overview of the statistical parameters for all analyses can be found in Table S2.

Regarding the effects of seedbed–forage interactions on weed density in 2021–2022, the combination of FSB 2 with ARBC 3, FSB 2 with ARM, and FSB 2 with ARBC 2 resulted in very low weed density (≤7 weeds m⁻²), while the next weed suppressive combinations were: FSB 1 with ARBC 3, FSB 2 with BCM, FSB 1 with ARBC 2, and FSB 1 with ARBC 1. Total weed density was highest (≥60 weeds m⁻²) in the NSB with BCM, NSB with ARBC 1, and FSB 1 with ARBC 1 subplots. Lower values were observed in NSB with ARM and NSB with ARBC 3 subplots (Figure 3).

3.2. Forage Yield in the First Harvest

At first harvest, forage yield was affected by all experimental factors, including years (p ≤ 0.001) and an interaction of year and seedbed (p ≤ 0.05). Interactions between year and forage and seedbed and forage influenced berseem clover biomass (p ≤ 0.001). The same was true for forage (p ≤ 0.01) and seedbed (p ≤ 0.001) factors. Weed biomass was influenced by year, seedbed, and forage (p ≤ 0.001), interaction between year and seedbed (p ≤ 0.01), and interaction between seedbed and forage (p ≤ 0.05; Table S3). Forage yield and biomass of berseem clover were 14% higher in 2020–2021 than in 2021–2022. In contrast, weed biomass increased by 36% in the second growing season (Figure 4a–c).

In the first harvest of both growing seasons, seedbed and forage affected forage yield, berseem clover biomass, and weed biomass (p ≤ 0.001). Berseem clover biomass was also influenced by the interaction between seedbed and forage in 2020–2021 (p ≤ 0.01) and 2021–2022 (p ≤ 0.001;

Table 4. Overall statistical analyses of degrees of freedom (for seedbed factor; for forage factor; for seedbed and forage interaction; for the error) and of the significance of effect (seedbed; forage; seedbed and forage interaction and tests performed) on forage yield, berseem clover, and total weed biomass. Data are presented separately for the two growing seasons (2020–2021 and 2021–2022).

Factors	DF 1	Forage Yield		Berseem Clover Biomass		Weed Biomass
		2020–2021	2021–2022	2020–2021	2021–2022	2020–2021	2021–2022
Seedbed (S)	2	0.0000	0.0001	0.0005	0.0003	0.0000	0.0001
Error (a) 2	6
Forage (F)	4	0.0000	0.0001	0.0000	0.0000	0.0001	0.0000
S × F	8	0.2547	0.5851	0.0048	0.0001	0.4917	0.1190
Error (b) 3	36
Total	59

¹ DF: degrees of freedom; ² Error (a): S × Block; ³ Error (b): F(S) × Block.

).

FSB 2 improved forage yield by 9% and 11% compared to FSB 1 and NSB, respectively, in 2020–2021. In 2021–2022, FSB 2 resulted in 14% and 17% higher forage yield than FSB 1 and NSB, respectively. In the first growing season, berseem clover biomass was highest in FSB 2 main plots and lowest in FSB 1 and NSB main plots. In the second growing season, FSB 1 increased berseem clover biomass by 7% compared to NSB. In addition, FSB 1 decreased weed biomass by 27% and 34% compared to NSB in 2020–2021 and 2021–2022, respectively. FSB 2 resulted in the lowest weed pressure in both years (

Table 5. Forage yield (kg ha⁻¹), biomass of berseem clover (kg ha⁻¹), and total weed biomass (g m⁻²) in the first harvest of 2020–2021 and 2021–2022.

Factors	Forage Yield (kg ha−1)		Berseem Clover Biomass (kg ha−1)		Weed Biomass (g m−2)
	2020–2021	2021–2022	2020–2021	2021–2022	2020–2021	2021–2022
Seedbed
NSB 1	6660.8 c 2 (117.9)	5554.2 b (148.2)	3078.6 b (155.4)	2527.0 c (113.4)	336.6 a (64.3)	526.7 a (54.6)
FSB 1	6818.5 b (123.6)	5690.4 b (135.6)	3139.4 b (153.5)	2718.8 b (89.2)	238.1 b (35.8)	347.7 b (39.7)
FSB 2	7510.8 a (126.6)	6701.0 a (192.8)	3574.6 a (116.8)	3161.3 a (201.9)	61.4 c (14.7)	125.4 c (32.6)
LSD0.05	100.9	277.8	159.8	175.2	39.0	81.9
Forage
BCM	6477.4 d (146.4)	5727.9 cd (169.4)	6477.5 a (146.4)	5727.9 a (169.4)	330.0 a (53.3)	502.4 a (53.1)
ARBC 1	6805.6 c (130.6)	5690.5 d (134.8)	4963.5 b (172.1)	3952.5 b (190.8)	255.6 ab (47.1)	454.9 a (34.6)
ARBC 2	7073.5 b (108.8)	5973.2 bc (145.2)	3022.2 c (236.8)	2613.0 c (246.9)	212.2 bc (41.3)	268.4 b (49.2)
ARBC 3	7437.0 a (123.0)	6322.0 a (139.9)	1857.8 d (150.1)	1718.5 d (66.9)	124.4 d (24.4)	215.1 b (30.0)
ARM	7189.9 b (104.8)	6195.7 ab (204.9)	0.0 e (0.0)	0.0 e (0.0)	138.1 cd (25.3)	225.6 b (44.6)
LSD0.05	216.1	271.3	281.5	226.9	83.1	76.1

¹ NSB: Normal seedbed, FSB 1: First false seedbed, FSB 2: Second false seedbed, BCM: Berseem clover monoculture, ARBC 1: First intercrop with annual ryegrass and berseem clover in a 25:75 ratio, ARBC 2: Second intercrop with annual ryegrass and berseem clover in a 50:50 ratio, ARBC 3: Third intercrop with annual ryegrass and berseem clover in a 75:25 ratio, ARM: Annual ryegrass monoculture (see text in Section 2.2 for details); ² Numbers followed by the same letter in the same column are not significantly different.

).

In 2020–2021, ARBC 3 increased forage yield compared to ARM and ARBC 2. ARM and ARBC 2 resulted in higher forage yield than ARBC 1. The lowest forage yield was observed in the BCM main plots. In 2021–2022, ARBC 3 increased forage yield by 5, 9, and 10% compared to ARBC 2, BCM, and ARBC 1, respectively. ARM was not different from ARBC 3. ARBC 2 and ARM also improved forage yield compared to ARBC 1.

As the number of days before sowing increased from FSB 1 to FSB 2 compared to NSB, forage yield increased, as indicated by the strong second-degree polynomial relationships between total weed density and days until sowing. This was observed for all forages in both experimental years (Figure 5).

In the first growing season (2020–2021), the coefficient of determination was highest in the ARM subplots (R² = 0.7799) and lowest in the ARBC 2 subplots (R² = 0.5199). In addition, about 61 and 74% of the variation in forage yield could be explained by the days elapsed until sowing in the ARBC 1 and ARBC 3 subplots, respectively. During 2021–2022, the strongest correlations between the dependent variable (forage yield) and the independent variable (days until sowing) were observed for ARBC 3 (R² = 0.8480) and also ARBC 1 (R² = 0.8211). The weakest correlation was observed for ARM (R² = 0.4987). As for the other two forages, an R² of 0.6494 and 0.7071 was observed for BCM and ARBC 2, respectively. Statistical parameters for all analyses are shown in Table S4.

For berseem clover biomass, forages differed significantly in descending order: BCM > ARBC 1 > ARBC 2 > ARBC 3 > ARM in both growing seasons. Weed biomass was 58 and 62% higher in the BCM subplots than in the ARM and ARBC 3 subplots in the first growing season, respectively. ARBC 3 reduced weed biomass by nearly 50% compared to ARBC 1. In addition, ARBC 2 suppressed weed biomass by 35% compared to BCM, but was not different from ARBC 1. Weed biomass was highest in the BCM and ARBC 1 subplots (≥450 g m⁻²) and lowest in the ARBC 2, ARM, and ARBC 2 subplots (215–268 g m⁻²) in 2021–2022.

Regarding the integrated effects of seedbed–forage interactions on the biomass of berseem clover, the combination of FSB 2 with BCM resulted in the highest biomass of berseem clover in both years, followed by FSB 1 with BCM and NSB with BCM. However, in 2021–2022, FSB 1 with BCM resulted in higher berseem clover biomass than NSB with BCM. In 2020–2021, some of the remaining combinations of seedbeds and forages differed in descending order: FSB 2 with ARBC 1 ≥ FSB 1 with ARBC 1 > NSB with ARBC 1 > FSB 2 with ARBC 2 > FSB 1 with ARBC 2 > FSB 1 with ARBC 2. The lowest values corresponded to the combinations of FSB 2, FSB 1, and NSB with ARBC. Similar observations were made in 2021–2022 (Figure 6).

3.3. Forage Yield in the Second Harvest

In the second harvest, the years, seedbeds, and their interaction had no effect on forage yield. In contrast, forage yield was affected by forage (p ≤ 0.001). Therefore, data were pooled across years but not across seedbeds because a significant interaction was found between seedbed and forage (p ≤ 0.05; Table S5). Subsequent analysis of data pooled across years by two-way analysis (seedbed by forage) ANOVA revealed significant effects of forage (p ≤ 0.001) and seedbed by forage interaction (p ≤ 0.05) on forage yield. Forage yield did not differ between seedbeds (p ≥ 0.05). Forage yield was 4, 6, 11, and 12% higher in ARBC 3 subplots than in ARBC 2, ARM, ARBC 1, and BCM subplots, respectively. ARM increased forage yield compared to ARBC 1 and BCM, but did not differ from ARBC 2 (

Table 6. The effects of seedbed (S) and forage (F) on forage yield in the second harvest. Data were pooled over 2020–2021 and 2021–2022. Forage yield data (kg ha⁻¹), pooled over 2020–2021 and 2021–2022 are also shown.

Factors	DF 1	Forage Yield
Seedbed (S)	2	0.2798
Error (a) 2	6
Forage (F)	4	0.0000
S × F	8	0.0489
Error (b) 3	36
Total	59
Factors		Forage Yield (kg ha−1)
Seedbed
NSB 4		3153.9 a 5 (46.6)
FSB 1		3189.6 a (49.1)
FSB 2		3206.9 a (48.6)
LSD0.05		74.2
Forage
BCM		2987.5 c (58.2)
ARBC 1		3036.7 c (27.4)
ARBC 2		3208.1 b (43.5)
ARBC 3		3407.3 a (56.3)
ARM		3277.7 b (55.2)
LSD0.05		87.6

¹ DF: degrees of freedom.; ² Error (a): S × Block; ³ Error (b): F(S) × Block; ⁴ NSB: Normal seedbed, FSB 1: First false seedbed, FSB 2: Second false seedbed, BCM: Berseem clover monoculture, ARBC 1: First intercrop with annual ryegrass and berseem clover in a 25:75 ratio, ARBC 2: Second intercrop with annual ryegrass and berseem clover in a 50:50 ratio, ARBC 3: Third intercrop with annual ryegrass and berseem clover in a 75:25 ratio, ARM: Annual ryegrass monoculture (see text in Section 2.2 for details). ⁵ Numbers followed by the same letter in the same column are not significantly different.

).

Moreover, the combination of FSB 2 with ARBC 3 gave the highest forage yield, followed by NSB with ARBC 3, FSB 1 with ARBC 3, and NSB with ARM. FSB 2 with ARM, FSB 1 with ARM, and FSB 1 with ARBC 2 were the next highest yielding seedbed and forage combinations. FSB 2 with BCM, ARBC 1, and ARBC 2 yielded less than 3200 (kg ha⁻¹), and the same was true for FSB 1 with ARBC 1. In addition, FSB 1 with ARBC 1, NSB with ARBC 1, and NSB with BCM had the lowest forage yields (Figure 7).

Biomass of berseem clover and weeds was influenced by the forage factor (p ≤ 0.001), but not by years, seedbeds, and their interactions (p ≤ 0.05; Table S3). Therefore, data were averaged across years and seedbeds and reanalyzed to evaluate the effects of forage factor on both parameters. Berseem clover as a monoculture (BCM) produced 2987.5 kg ha⁻¹ biomass, while ARBC 1 produced 26% less berseem clover biomass. ARBC 2 resulted in nearly half the BCM biomass, while ARBC 3 approached 1000 kg ha⁻¹ production. ARBC 3 suppressed weed biomass by 47 and 56% compared to ARBC 1 and BCM, respectively, but did not differ from ARBC 2. In addition, ARBC 1 caused a slight reduction (17%) in weed biomass compared to BCM (Figure 8).

3.4. Cumulative Forage Yield from Two Harvests

Years influenced cumulative forage yield (p ≤ 0.01) and biomass of berseem clover (p ≤ 0.05), while both parameters were influenced by seedbed and forage factors (p ≤ 0.001). A significant interaction between seedbed and forage was found for berseem clover biomass (p ≤ 0.001; Table S6). Forage yield was influenced by seedbed and forage factors in both 2020–2021 and 2021–2022 (p ≤ 0.001). Seedbed influenced berseem clover biomass in 2020–2021 (p ≤ 0.001) and 2021–2022 (p ≤ 0.01). The effects of forage (p ≤ 0.001) and seedbed–forage interaction (p ≤ 0.01) on berseem clover biomass in both growing seasons were also significant (

Table 7. Overall statistical analyses of degrees of freedom (for seedbed factor; for forage factor; for seedbed and forage interaction; for the error) and of the significance of effect (seedbed; forage; seedbed and forage interaction and tests performed) on cumulative forage yield and biomass of berseem clover from two harvests. Data are presented separately for the two growing seasons (2020–2021 and 2021–2022).

Factors	DF 1	Forage Yield		Berseem Clover Biomass
		2020–2021	2021–2022	2020–2021	2021–2022
Seedbed (S)	2	0.0000	0.0009	0.0001	0.0023
Error (a) 2	6
Forage (F)	4	0.0000	0.0000	0.0000	0.0000
S × F	8	0.2620	0.5424	0.0051	0.0064
Error (b) 3	36
Total	59

¹ DF: degrees of freedom; ² Error (a): S × Block; ³ Error (b): F(S) × Block.

).

FSB 2 increased cumulative forage yield from two harvests by 7% and 17% compared to FSB 1 in the first and second growing seasons, respectively. Compared to NSB main plots, forage yield was 8% higher on FSB 2 main plots in 2020–2021 and 12% higher in 2021–2022. In 2020–2021, FSB 1 improved forage yield compared to NSB, but this result was not observed in 2021–2022. As for berseem clover cumulative biomass in the first growing season, it increased by 8% and 10% in FSB 2 main plots compared to FSB 1 and NSB main plots, respectively. Similar results were obtained in the second growing season.

In 2020–2021, ARBC 3 yielded more than 10,840 kg ha⁻¹ of biomass and was the most productive forage, followed by ARM and ARBC. No difference was observed between ARM and ARBC. ARBC 1 yielded less compared to the above forages. BCM was the least productive forage with less than 9500 kg ha⁻¹ biomass. In 2021–2022, forage yield was 6, 10, and 11% higher for ARBC 3 than ARBC 2, BCM, and ARBC 1, respectively. ARBC 2 tended to be more productive than ARM, but the difference was not statistically significant. ARM also increased forage yield compared to ARBC 2, BCM, and ARBC 1. Compared to BCM and ARBC 1, ARBC 2 produced a slight but significant increase in cumulative forage yield from two harvests, while BCM and ARBC 1 yields were similar. In addition, ARBC 1 produced 23% and 30% less berseem clover biomass compared to berseem clover monoculture (BCM) in 2020–2021 and 2021–2022, respectively. ARBC 2 produced about half the BCM biomass in both years; intercrop ARBC 3, which was dominated by annual ryegrass, produced the least amount of berseem clover biomass in both growing seasons (

Table 8. Cumulative forage yield (kg ha⁻¹) and biomass of berseem clover (kg ha⁻¹) from two harvests in 2020–2021 and 2021–2022.

Factors	Forage Yield (kg ha−1)		Berseem Clover Biomass (kg ha−1)
	2020–2021	2021–2022	2020–2021	2021–2022
Seedbed
NSB 1	9832.9 c 2 (174.0)	8689.9 b (231.5)	4595.8 b (205.0)	4041.4 b (192.1)
FSB 1	9999.1 b (181.1)	8888.9 b (211.9)	4667.2 b (189.8)	4231.2 b (127.7)
FSB 2	10,735.2 a (184.4)	9890.4 a (284.5)	5103.4 a (126.7)	4861.1 a (202.0)
LSD0.05	147.9	423.4	125.2	255.2
Forage
BCM	9446.8 d (213.8)	8733.6 d (257.9)	9446.8 a (213.8)	8733.6 a (257.9)
ARBC 1	9878.9 c (189.9)	8681.6 d (205.0)	7242.3 b (215.7)	6055.6 b (301.7)
ARBC 2	10,305.3 b (158.0)	9157.5 b (222.5)	4468.6 c (251.4)	4096.5 c (188.3)
ARBC 3	10,845.9 a (179.1)	9727.8 a (215.5)	2876.4 d (188.3)	2703.7 d (121.8)
ARM	10,459.4 b (158.2)	9481.6 ab (312.3)	0.0 e (0.0)	0.0 e (0.0)
LSD0.05	316.8	412.5	353.3	366.0

¹ NSB: Normal seedbed, FSB 1: First false seedbed, FSB 2: Second false seedbed, BCM: Berseem clover monoculture, ARBC 1: First intercrop with annual ryegrass and berseem clover in a 25:75 ratio, ARBC 2: Second intercrop with annual ryegrass and berseem clover in a 50:50 ratio, ARBC 3: Third intercrop with annual ryegrass and berseem clover in a 75:25 ratio, ARM: Annual ryegrass monoculture (see text in Section 2.2 for details); ² Numbers followed by the same letter in the same column are not significantly different.

).

Regarding the combined effects of seedbed and forage interactions on cumulative berseem clover biomass from two harvests, the combination FSB 2 with BCM resulted in the highest berseem clover biomass, and the next most productive combinations were FSB 1 with BCM and NSB with BCM. These results were the same in 2020–2021 and 2021–2022. In 2021–2022, FSB 1 with BCM increased berseem clover biomass compared to NSB with BCM. In 2020–2021, FSB 2 with ARBC 2 provided higher berseem clover biomass than FSB 1 with ARBC 2 and NSB with ARBC 2, but this was not observed in 2021–2022. In both growing seasons, FSB 2 with ARBC 3, FSB 1 with ARBC 2, and NSB with ARBC 3 resulted in lower berseem clover biomass compared to the above combinations (Figure 9).

4. Discussion

One of the major findings of the current study was that FSB 2 reduced the density of sterile oat and wild mustard compared with NSB in both growth periods. These results are consistent with recent studies in barley (Hordeum vulgare L.) where false seedbed resulted in 67–78% and 89–91% less biomass in sterile oat and wild mustard, respectively [24]. Both false seedbed manipulations (FSB 1 and FSB 2) reduced total weed density compared to NSB, as in previous field trials conducted under soil and climatic conditions in Greece [23]. False seedbeds work by getting the non-dormant seeds at the soil surface to germinate, and then controlling the emerging weed seedlings, without bringing up more non-dormant weed seeds from deeper soil profiles on the soil surface [26]. As a result, weed density and biomass in the field decrease significantly, as also shown in this study. At the first forage harvest, weed biomass decreased in both FSB 1 and FSB 2 subplots compared to NSB subplots. These results are consistent with those of De Cauwer et al. [38], who also indicated that false seedbed is a cultural practice for agroecological weed management that reduces weed biomass at harvest. In another recent study conducted on wheat (Triticum aestivum L.), Shahzad et al. [39] found that a false seedbed significantly reduced weed density and biomass compared to conventional seedbed manipulations.

Another observation was that FSB 1 also reduced total weed density to some degree compared to NSB in most evaluations, and FSB 2 caused a further reduction in weed density compared to FSB 1. Strong second-degree polynomial relationships were observed between total weed density and days until sowing, indicating that as the number of days until sowing increased in FSB 1 and FSB 2, total weed density decreased. The reason for this result is that more weed seedlings germinated due to the extension of the period between the first tillage operations and sowing, and were subsequently controlled by shallow tillage immediately before sowing. Similar results are reported by Sindhu et al. [40], who found that a false seedbed was more effective as a weed management practice when weed control was done by shallow tillage 14 days compared to 7 days before sowing in rice. Such findings also agree with the corresponding of Shem–Tov et al. [41] in spinach. However, the ideal timing for pre-sowing weed control should be further investigated as it depends on soil and climatic conditions in a particular growing area [26].

Because FSB 2 and FSB 1 reduced weed density and biomass compared to NSB, these seedbed manipulations resulted in higher forage yields, as observed in previous forage crop trials [18]. Along with the increase in forage yield, berseem clover biomass also increased in subplots FSB 1 and especially FSB 2. Moreover, as mentioned earlier, a false seedbed had no effect on forage yield and, consequently, on the biomass of berseem clover in the second harvest. However, the positive effects of the false seedbed on the above parameters in the first harvest improved the cumulative forage yield and berseem clover biomass from two harvests. These results agree with another recent study on sulla (Hedysarum coronarium L.), a legume forage crop with multiple uses [25]. Specifically, these authors found that a false seedbed, randomly established, significantly reduced weed biomass and caused a significant increase in biomass yield in the first sulla harvest compared to seeding immediately after seedbed preparation. In addition, Naeem et al. [42] reported that a false seedbed compared to a conventional seedbed preparation resulted in lower weed density and higher yields in barley. Similar results were reported by De Cauwer et al. [38] in spinach. In addition, FSB 1 increased forage yield compared to NSB, while FSB 2 further improved forage yield compared to FSB 1. Forage yield increased with the increase in the number of days until sowing when preparing a false seedbed, as indicated by the strong second-degree polynomial relationships between forage yield and the days until sowing. This can be attributed to the fact that weed density decreased by increasing the days until sowing in false seedbed plots (FSB 1 and FSB 2), as explained above. Although these results are promising, in agricultural areas with unfavourable weather conditions, delaying sowing to prepare a false seedbed can result in significant yield losses [43].

A general observation regarding weed infestation was that weed density and weed biomass were higher in the first harvest of 2021–2022 compared to 2020–2021, which could be due to higher monthly rainfall in October, November, and December 2021 compared to October, November, and December 2022. It should be noted that at the second harvest, a false seedbed was expected to provide no additional benefit to weed control and forage yield as winter weeds were mowed and removed from the field after cutting and new summer weeds (mainly Chenopodium album L. and Setaria viridis L.) emerged in an already established stand. The shift in weed flora between different harvests of forage crops is consistent with the observations of Kanatas et al. [18].

Regarding the effects of forage factor on weed density and biomass, intercrops ARBC 2 and ARBC 3 suppressed weeds more than ARBC 1. This may be attributed to the higher proportion of annual ryegrass in these intercrops compared to ARBC 1. Annual ryegrass is more aggressive in growth compared to berseem clover. In general, legumes are less competitive than cereals and grasses [44]. In such cereal–legume intercrops, small grains are usually the stronger competitors against weeds due to their earlier germination, relatively rapid initial growth, tillering ability, and extensive root systems [45]. Therefore, the mixtures containing 50% and 75% annual ryegrass were more competitive against weeds than ARBC 1, which consisted of 25% annual ryegrass and 75% berseem clover. The monoculture of annual ryegrass (ARM) also suppressed weeds better than the monoculture of berseem clover (BCM). ARM showed a higher potential to suppress weeds than the intercrops ARBC 1 and ARBC 2. This is consistent with MacLaren et al. [46], who found that monocultures suppress weeds better than intercrops. These authors attributed this to the higher biomass production of monocultures and emphasized that, in some cases, biomass production may be the mechanism for weed suppression rather than plant functional diversity. However, the intercrop ARBC 3 was either more or at least as competitive as ARM. It is likely that this intercrop was highly competitive because the proportion of annual ryegrass was very high, while the simultaneous presence of berseem clover contributed about 25% of the total ground cover. In addition, the presence of berseem clover in the mixture increased the range of nutrients taken up by the intercrop, resulting in greater weed suppression compared to a monoculture of annual ryegrass [13].

ARBC 3 was the most productive forage in both harvests in both years and also produced the highest cumulative forage yield from two harvests. Berseem clover may have provided nitrogen to the annual ryegrass through biological nitrogen fixation from the atmosphere. It is likely that this enhanced the growth of the annual ryegrass, while the presence of berseem clover in the mixture at 25% further contributed to the total forage yield. As pointed out by Glaze–Corcoran et al. [16], one of the advantages of including legumes in intercropping is that they can improve the growth of the species involved by supplying nitrogen. Moreover, monoculture of annual ryegrass was more productive than monoculture of berseem clover. This result is in contrast to previous studies conducted in regions with similar soil and climatic conditions [7,8,9]. The explanation is that in these studies, berseem clover was able to grow throughout the growing season without competition because weeds were removed from the field. However, in the present study, the high weed pressure hindered its productivity. As also noted by Pathan et al. [47], due to its slow growth in the initial stage, berseem clover can suffer severe yield losses due to high weed competition.

Intercrops ARBC 2 and ARBC 3 were also more productive than BCM because the proportion of annual ryegrass in these mixtures was 50% and 75%, respectively, resulting in greater weed suppression and forage production. In addition, these two intercrops were balanced, and berseem clover biomass was not suppressed by annual ryegrass, even in the ARBC 3 intercrop. This may be attributed to the characteristics of cultivars of both species that were selected for the trial, as already explained before. This emphasizes the importance of selecting cultivars with suitable traits to form intercrops that are competitive with weeds, have high yield potential, and minimal interspecific competition [16,48]. This is especially critical for cereal–legume intercrops, as the aggressiveness of cereals can hinder legume growth and biomass production [4,11].

5. Conclusions

The current study has shown that a false seedbed is a valuable cultural practice for agroecological weed management in cereal–legume forage intercrops and monocultures. In addition, as the number of days until sowing increased in FSB 1 and FSB 2, total weed density decreased. The reason for this result is that more weed seedlings germinated by extending the period between initial tillage and sowing, and were subsequently controlled by shallow tillage immediately prior to seeding. Reverse trends were observed for forage yields, with the highest values on FSB 2 main plots, the lowest on NSB main plots, and medium yields on FSB 1 main plots. Moreover, in annual ryegrass–berseem clover intercrops, increasing the proportion of the grass species can lead to higher weed suppression and consequently higher forage yields. This suggests that seed rate manipulations can be useful in terms of weed suppression in mixed intercropping systems for forage production. Further research is needed to evaluate low-input cultural practices for agroecological weed management in economically important forage crops in the Mediterranean region.