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. 2026 May 28;16:24559. doi: 10.1038/s41598-026-55354-7

Meta-analysis of the effects of relay and double-cropping systems on weed control and crop production in arable lands

Azadeh Khamsei 1, Elias Soltani 1, Fatemeh Benakashani 1,✉
PMCID: PMC13454471  PMID: 42209659

Abstract

Relay and double cropping offer a pathway for ecological intensification by improving weed suppression and maintaining crop production. Although numerous studies have examined the effects of relay and double cropping on crop yield and weed management, a comprehensive synthesis is needed to summarize the overall impact. This research presents a meta-analysis investigating the effects of relay and double cropping on weed control traits and crop production outcomes. A total 49 international articles reporting relevant data were selected and analyzed. Both systems significantly suppressed weeds. Specifically, the relay cropping system reduced weed biomass by 78% and density by 64%, while the double cropping system led to reductions of 95% in biomass and 66% in density across diverse environmental conditions. While double cropping was more effective at reducing weed biomass, both systems had a non-significant impact on weed species richness. Ultimately, the choice of system involves a trade-off, as the superior weed suppression of double cropping came at the cost of a significant reduction in crop production (yield), whereas relay cropping did not significantly impact yield. Future research should refine relay cropping systems through site-specific management and crop breeding to optimize their role in sustainable agriculture.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-026-55354-7.

Keywords: Crop productivity, Ecological intensification, Integrated weed management, Weed biomass

Subject terms: Ecology, Ecology, Environmental sciences, Plant sciences

Introduction

Optimizing the use of available arable land has become a central goal in modern agriculture for global food security. In regions with extended growing seasons, farmers can harness the full potential of their land by cultivating two (double cropping) or even three (triple cropping) crops sequentially within a single agricultural year, thereby enhancing total annual crop yields, increase farm income, and improve resource-use efficiency1–3. The growing adoption of these systems is supported by advances in agronomic practices and recent climatic trends, such as warmer temperatures and prolonged frost-free periods as a result of climate change, which have extended the growing season in many temperate and subtropical regions4,5.

However, despite these climatic advantages, many regions still experience critical environmental constraints that limit the feasibility and success of continuous cropping systems. These include summer droughts, high temperature stress, and unpredictable autumn precipitation, all of which can shorten the effective growing season or create unsuitable conditions for establishing a second crop6. In such cases, reliance on a single crop per year—sole cropping—can lead to prolonged fallow periods, during which the soil remains bare and vulnerable to degradation. This condition fosters a range of agronomic and ecological issues, including soil erosion, nutrient leaching, and inefficient utilization of available water, solar radiation, and nutrients2,7,8.

To overcome these limitations and improve cropping intensity under challenging conditions, relay cropping, a strategy where a second crop is sown into a standing primary crop before its harvest, has emerged as a promising alternative strategy5. In this system, a second crop is sown into a standing primary crop before it is harvested, creating a temporal overlap between the two cropping phases. Relay cropping has been shown to offer effective biological weed suppression, largely due to increased crop canopy cover, enhanced competition for light, water, and nutrients, and disruption of weed life cycles5,9,10. By maintaining soil cover and biomass throughout most of the season, relay systems reduce the niche space available for weeds to establish and proliferate, thereby decreasing weed density and biomass. This not only promotes ecological sustainability by potentially reducing the reliance on synthetic herbicides but also contributes to multifunctional benefits including soil protection, yield stability, and improved system resilience11,12. Typically, the first crop is a high-value cash crop, and the second may serve purposes such as grain production, green manure, biomass accumulation, or soil coverage5,7,13,14. This concurrent growth phase facilitates efficient resource partitioning, reduces land idling between harvests, and potentially extends the period of photosynthetic activity in the field12. Although the yield of individual crops in sole cropping systems may sometimes exceed that observed in relay systems due to reduced interspecific competition, the aggregate yield (land equivalent ratio) of relay cropping is frequently superior7,15–17.

Among the many challenges faced in intensive and sustainable agriculture, weed infestation remains one of the most significant yield-limiting factors. On a global scale, weeds are estimated to reduce crop yields by about 34%, with losses reported as high as 40% depending on weed density, emergence timing, species, and crop type18–20. In the USA and Canada, yield losses from weed interference average 50–52% in major crops such as soybean and corn21–23. At a global scale, potential yield losses in wheat due to weed competition can be substantial—often exceeding 30% in the absence of effective weed management—although the magnitude of losses varies widely depending on agronomic practices and environmental conditions24. In addition to direct yield losses, the financial costs associated with weed control measures—herbicides, mechanical tillage, and labor—are significant, for example the Weed Science Society of America estimates that weeds cost U.S. farmers billions of dollars annually in lost production and control expenditures25,26. Furthermore, weeds challenge sustainable agriculture both immediately and in the long term. In the short term, they compete with crops for soil moisture and temporarily sequester nutrients. Over the long term, they contribute to sustainability concerns by creating persistent reservoirs for pests and diseases and by consistently reducing harvest efficiency20.

In addition to relay cropping, double cropping is widely used to intensify cropping systems and improve economic returns2. This strategy not only increases land productivity but also contributes to weed suppression through resource depletion and temporal disruption27–29. By minimizing the duration of fallow periods, double cropping restricts opportunities for weed seed germination and emergence23,30. In addition to increasing land productivity, integrated practices in double-cropping—such as the application of spent coffee grounds as a mulch—can effectively suppress weeds and enhance soil fertility31. Some double cropping systems integrate cover crops between main crop cycles, which further enhances weed suppression by maintaining continuous ground cover and improving soil health32. Importantly, the success of weed management in double cropping depends on appropriate species selection, precise planting and harvesting timing, and effective agronomic management23,33.

Despite the promising benefits of relay and double cropping for weed management and yield improvement, reported outcomes vary significantly across studies due to differences in crop species, climate conditions, management practices, and weed communities. To synthesize this fragmented body of knowledge, meta-analysis offers a robust quantitative framework. A meta-analysis aggregates results from multiple independent studies to produce a comprehensive and statistically powerful estimate of the overall effect size34,35. This approach enables the identification of general patterns, moderating factors, and sources of variability across diverse agroecological settings32,34,36.

Given the increasing demand for sustainable and resilient agricultural practices, understanding the influence of alternative cropping systems on weed dynamics and crop productivity is of critical importance. In this study, we tested the hypothesis that relay and double-cropping systems contribute to weed suppression by altering competitive dynamics, but that their effects on crop yield are system-dependent. Accordingly, the objective of this study was a quantitative meta-analysis evaluating the effects of relay and double-cropping systems on weed control and crop production across diverse crop species and environmental conditions.

Material and methods

Data sources

The literature search was primarily conducted using the web of science (WOS) database, supplemented by the scientific information database (SID) to identify relevant studies within Iran. The targeted studies were international scientific research articles published between 1950 and 2023, retrieved using the keywords “Relay cropping + Weed” and “Double cropping + Weed.” During the initial search, all articles containing these keywords or those deemed relevant to the main research topic were recorded for further screening. We operationally defined cropping systems based on temporal overlap between successive crops within a single agricultural calendar year. Double cropping was defined as a system where two distinct crops are grown sequentially without temporal overlap, i.e., the second crop is planted after complete harvest of the first crop. In contrast, relay cropping was defined as a system with temporal overlap, where the second crop is established before the harvest of the first crop. During the screening process, we recognized that many primary studies did not explicitly use these standardized terms. Therefore, we extracted the following information from each study to classify cropping systems consistently: (1) planting and harvest dates for each crop, (2) descriptions of cropping sequences in the Methods or Results sections, (3) phenological stages and growing season durations reported in tables or figures, and (4) any explicit mention of temporal overlap or sequential planting patterns. When planting and harvest dates were not explicitly reported, we inferred the cropping pattern from descriptions of field management practices and crop rotation schedules. Studies with insufficient information to determine the presence or absence of temporal overlap were excluded from the analysis.

The selected articles were carefully screened based on predefined inclusion and exclusion criteria to ensure only studies suitable for meta-analysis were included. Studies eligible for inclusion were original research articles published in peer-reviewed journals that reported quantitative data on at least one of six key traits. These traits included four weed-related parameters—weed count, density, species richness, and biomass—and two crop-related parameters—crop biomass and crop yield. Weed density was defined as the number of individual weeds per unit area (plants m⁻2), while weed count referred to the total number of weeds recorded within the reported sampling unit when area-based standardization was not possible. Reports of the number of weed species were treated separately as weed species richness. Furthermore, the studies had to provide sufficient statistical information, including mean values for both control (sole cropping) and treatment (relay or double cropping) groups, along with sample sizes or number of replicates. Only studies focusing on arable land systems applying relay or double-cropping practices were considered. Articles published in either English or Persian were included.

Studies were excluded if they lacked sufficient quantitative data to calculate effect sizes or if they were reviews, meta-analyses, conference abstracts, or unpublished theses. Additionally, studies exclusively addressing non-arable systems, such as forestry or horticulture unrelated to arable cropping, were omitted. Studies combining relay or double cropping with other interventions like herbicides or mechanical weeding, without clearly separating their effects, were also excluded.

The initial search retrieved 157 articles using the keywords “Relay cropping + Weed” and 400 articles using “Double cropping + Weed.” After removing duplicate records and screening for relevance and data completeness, irrelevant or low-quality studies were excluded according to the above criteria (see Fig. 1 for the screening process). Ultimately, 49 articles met all inclusion criteria and provided the necessary data for conducting the meta-analysis.

Fig. 1.

Fig. 1

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PRISMA flow diagram illustrating the selection process of studies included in the meta-analysis.

Data extraction

To calculate effect sizes accurately, instances where studies included multiple experimental treatments, crop combinations, or site-specific conditions were treated as independent observations, thereby capturing within-study variability and ensuring a robust analysis. Quantitative data reported only in graphical form were extracted using Digimizer software (MedCalc Software Ltd., Belgium).

We collected several explanatory variables related to management and environmental conditions. These included irrigation regimes (irrigated or rainfed), cropping system (relay or double cropping), and tillage method (conventional or no-tillage, based on study descriptions). Soil characteristics, including texture, pH, and salinity, were also collected. Soil texture was classified into four categories: Category A (coarse-textured: sandy clay, sandy clay loam, sandy loam, loamy sand, sand); Category B (silt-dominated: silty clay, silty clay loam, silty loam, silt); Category C (medium-textured: loam, clay loam); and Category D (fine-textured: heavy clay). Furthermore, soil pH was categorized as acidic, neutral, or alkaline, and salinity as saline or non-saline. The extracted information from all included studies is summarized in Table 1 and distribution of the locations is indicated in Fig. 2.

Table 1.

A summary of the studied included in the present meta-analysis. A dash (–) indicates that no record was available. RC, relay cropping; DC, double-cropping. Soil texture categories: A (coarse-textured: sandy clay, sandy clay loam, sandy loam, loamy sand, sand); B (silt-dominated: silty clay, silty clay loam, silty loam, silt); C (medium-textured: loam, clay loam); D (fine-textured: heavy clay).

Author and Year Irrigation type Cropping system Soil texture Soil pH Soil salinity Tillage type
Abbas et al.29 Irrigated DC C Alkaline Non-saline –
Adeniyan and Ayoola37 Rainfed RC – – – Conventional
Adim et al.38 Irrigated RC A Neutral Non-saline Conventional
Amossé et al.39 Rainfed RC B – – No-tillage
Bainard et al.40 Rainfed DC D - – Conventional
Baldé et al.15 Rainfed RC C – – Conventional
Blackshaw et al.41 Rainfed RC A Neutral – No-tillage
Bolandi et al.42 Rainfed DC C Alkaline – Conventional
Borrelli and Pecetti43 Irrigated DC A Neutral – Conventional
Bunna et al.44 Irrigated DC – Alkaline – Conventional
Correia et al.45 Rainfed RC A Neutral – Conventional
DeVore et al.46 Rainfed DC B Neutral – No & Conventional
Efthimiadou et al.47 Irrigated DC C Neutral – Conventional
Evans et al.48 Rainfed RC – Acidic – –
Hoerning et al.49 – RC B Neutral – No-tillage
Iqbal et al.50 Irrigated DC B - – –
Jemison et al.51 Rainfed DC A Neutral – Conventional
Johnson et al.27 Rainfed DC C Acidic – –
Koskey et al.52 Rainfed RC A Alkaline – Conventional
Leclère et al.28 Rainfed DC – – – –
Leoni et al.10 Rainfed RC B – – Conventional
Mashingaidze et al.53 Rainfed DC C Neutral – Conventional
Mason et al.54 Rainfed DC D – – No-tillage
Mauli et al.55 Irrigated DC – – – No-tillage
Mennan et al.56 Rainfed DC B Neutral – Conventional
Mhlanga et al.57 Rainfed RC D - – Conventional
Mischler et al.58 Rainfed DC B Neutral – No-tillage
Morris & Parrish,59 Rainfed DC B - – No-tillage
Nourbakhsh et al.60 Irrigated DC B Alkaline Non-saline –
Pinnamaneni et al.61 Rainfed DC B Neutral – No-tillage
Puig et al.62 Irrigated RC A Acidic Non-saline –
Punyalue et al.63 Rainfed DC A Acidic – No-tillage
Qayyum et al.64 Rainfed RC – – – Conventional
Reda et al.65 – RC – – – Conventional
Roslon & Fogelfors,66 Irrigated RC D – – Conventional
Saito et al.67 Irrigated RC – Neutral – No-tillage
Saito et al.68 Rainfed RC A _ – No-tillage
São Miguel et al.69 Rainfed DC – Neutral Saline No and Conventional
Schoofs & Entz,70 Rainfed DC – _ – No-tillage
Scopel et al.71 Irrigated RC – Neutral – –
Su et al.72 Rainfed RC C Neutral – –
VanGessel et al.73 – DC B Neutral – No and Conventional
Vidal & Bauman,74 Rainfed DC B Neutral – No tillage
Vrignon-Brenas et al.9 Rainfed RC B – – Conventional
Vrignon-Brenas et al.75 Irrigated RC and DC C – – Conventional
Webster et al.76 – DC A – – Conventional
Workayehu & Wortmann,77 Rainfed DC C Neutral – Conventional
Yu et al.16 Irrigated RC A Neutral – –
Zougmoré et al.78 Rainfed RC A Acidic Saline Conventional
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Fig. 2.

Fig. 2

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Geographical distribution of the study locations worldwide.

Meta-analysis

Individual effect sizes were computed as log ratios (lnR) for each response variable. Each value of lnR represents the natural logarithm of the ratio of the mean value of a treatment group (RC and DC; Inline graphic) to the mean value of the corresponding control group (sole cropping; Inline graphic):

graphic file with name d33e1370.gif

The lnR is a widely adopted metric in meta-analyses for expressing treatment effects on a consistent scale in agriculture science34. Values of lnR were derived for each response variable (weed count, weed density, weed species richness, and weed biomass, crop biomass and crop yield) and each study from the extracted data. For crop biomass and yield, effect sizes were calculated separately for each component crop in both relay cropping and double cropping systems. When two crops were grown within the same agricultural year, the yield of each crop was treated as a separate observation rather than combining them into a single annual productivity value. In cases where the component crops differed in economic or biophysical function, such as grain and forage crops, each was compared only with its corresponding sole-crop counterpart.

For each response variable, the mean value of lnR and its 95% confidence intervals (CI) was estimated with the rma() function of the metafor package (Viechtbauer, 2010) using the R software (version 4.2.3). Following Borenstein et al.79, we defined a hierarchical statistical model including a random study effect as follows:

Inline graphic, with Inline graphic and Inline graphic

With Inline graphic was the log ratio in study i, i = 1, …, n, μ was the mean effect size, Inline graphic and Inline graphic were the between-study and within-study variances, respectively, and n was the total number of studies. The values of Inline graphic, i = 1, …, n, were estimated from the sample sizes extracted from the n selected studies. The variance Inline graphic—describing the heterogeneity of Inline graphic across studies—was estimated by Restricted Maximum Likelihood with the rma function. Then, the mean value of lnR (i.e., μ) was estimated with rma as the weighted sum of Inline graphic, using weights expressed as Inline graphic. The heterogeneity of the effect sizes (i.e., the variability of Inline graphic across studies) was tested using a Q statistical test79 with rma. This approach was implemented for each response variable (weed count, weed density, weed species richness, weed biomass, crop biomass and crop yield), separately.

To facilitate the understanding and interpretation of the results, we expressed the mean effect size (and its 95% confidence interval) as a percentage of variation of the response attributable to a crop in relay cropping to the same crop in sole cropping. This computation was applied to all the assessed variables by back-transforming the estimated mean log ratio in percent change as follows34,35:

graphic file with name d33e1504.gif

A positive or negative percentage denotes an increase or decrease in the respective measured response, respectively. Publication bias was assessed using funnel plots (generated by the function funnel of rma) to visually evaluate potential asymmetry. In cases where asymmetry was suspected, we applied the trim-and-fill method (function trimfill in the metafor package) to estimate the number of potentially missing studies and to assess the robustness of the overall effect size. The symmetry of most plots suggested a low risk of publication bias; however, for some response variables, the small number of studies reduced the reliability of these assessments.

Subgroup analyses

To explore potential sources of heterogeneity among the selected studies, subgroup analyses were conducted for several explanatory variables listed in Table 1 above related to cropping system, irrigation regime, soil characteristics, and tillage practices. These analyses were implemented using the subset argument of the rma function in the metafor package80. Each subgroup was evaluated separately to estimate the mean effect size and corresponding 95% confidence interval.

Cropping systems were classified as relay or double cropping, and irrigation as irrigated or rainfed, based on the management practices reported in the original studies. By applying these subgroup categories, we aimed to identify how environmental and management factors influence the six key response variables assessed in this meta-analysis. The results from these subgroup analyses provided insights into the conditions under which cropping systems are more effective in suppressing weeds and enhancing crop performance.

Results

Weed biomass

A total of 48 studies comprising 384 observations were included in the meta-analysis to evaluate the effects of relay cropping and double-cropping systems on weed biomass. Weed biomass exhibited significant heterogeneity across studies, with a Q value of 1293.39 (fixed-effect) and 1034.77 (random-effect), both highly significant at p < 0.01. The corresponding I2 values were 70.39% and 62.99%, indicating considerable variability beyond sampling error (Table 2). Subgroup analysis decreased heterogeneity in several categories under the random-effects model (Table S1). Significant variability in weed biomass was detected across most subgroups, with heterogeneity often moderate to high under the fixed-effect model, as shown by I2 values ranging from 36.89% to 75.57% and significant Q statistics in most cases (p < 0.05 or p < 0.01) (Table S1).

Table 2.

Heterogeneity results of effect sizes for the studied traits based on Q-test and I2 statistics. Both fixed-effect and random-effect models are reported. Q = Cochran’s Q statistic; I2 = proportion of total variation due to heterogeneity.

Trait QFixed QRandom I2Fixed (%) I2Random (%) No. observations No. studies
Weed biomass 1293.39** 1034.77** 70.39 62.99 384 48
Weed density 588.85** 277.02** 69.58 38.63 171 15
Weed count 251.08** 76.36 70.93 4.40 74 8
Weed species richness 85.57** 49.26 48.58 10.67 45 7
Crop yield 284.79 229.53 10.46 0.00 256 40
Crop biomass 1259.29** 374.88** 87.93 59.45 153 25
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**Significant at 1% level; significant at 5% level.

Overall, relay and double-cropping systems significantly reduced weed biomass by an average of 89.2% (confidence interval 95% = − 91% to − 88%) compared to sole cropping (Fig. 3). When analyzed separately, relay cropping reduced weed biomass by 74.8% (95% CI = − 78% to − 71%), while double cropping reduced weed biomass by 93.4% (95% CI = − 94.9% to − 91.8%). This suppressive effect was consistent across all environmental and management conditions examined, including variations in soil texture, salinity, irrigation regime, and tillage method.

Fig. 3.

Fig. 3

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Estimated percentage changes in four weed-related traits, including (A) weed biomass, (B) weed density, (C) weed count, and (D) weed species richness under relay cropping and double cropping systems compared to sole cropping (monoculture). The panels show meta-analysis results for: weed biomass, weed density, number of weeds, and weed species richness. Changes are grouped by experimental conditions, including, cropping system, irrigation type, tillage system, soil salinity, soil pH, and soil texture. Error bars represent 95% confidence intervals. Soil textures are coarse-textured soils (Soil_a), silt-dominated soils (Soil_b), medium-textured soils (Soil_c), and fine-textured soils (Soil_d).

Under rainfed conditions, weed biomass was reduced by 93% (confidence interval 95% = − 91.7% to − 94.4%), a significantly greater reduction than the 48% (confidence interval 95% = − 57.5 to − 40.4) observed under irrigated conditions (Fig. 3A). Both conventional and no-tillage systems significantly reduced weed biomass compared with sole cropping, although no significant difference was observed between the two tillage practices. Weed suppression in saline soils under relay and double-cropping systems was significantly greater than in non-saline soils (Fig. 3A). However, this result should be interpreted with caution, as only six studies (106 observations) reported soil salinity data, underscoring the need for further research in this area (Table S1). Weed biomass suppression ranged from 30% (95% CI = − 56% to − 5%) in fine-textured soils to nearly 76% (95% CI = − 80.5% to − 72.8%) in silt-dominated soils.

Regarding soil pH, relay and double cropping in neutral soils resulted in a 94.6% (95% CI = − 96% to − 93.2%) reduction in weed biomass compared with sole cropping (Fig. 3A). In contrast, reductions in acidic and alkaline soils were 71% (95% CI = − 82% to − 60%) and 64% (95% CI = − 73% to − 55%), respectively. The difference in weed suppression between neutral and non-neutral pH soils was statistically significant. Double cropping was more effective than relay cropping in suppressing weed biomass, with reductions of 94% and 75%, respectively—a statistically significant difference.

Weed density

Weed density showed significant heterogeneity (Q = 588.85 and 277.02; I2 = 69.58% and 38.63%), reflecting moderate to high between-study variability. The number of weeds also had a significant Q value under the fixed-effect model (Q = 251.08; p < 0.01) with a high I2 (70.93%), but low heterogeneity under the random-effects model (I2 = 4.40%), suggesting that the variation was mostly explained by sampling error (Table 2). The heterogeneity analysis of studies on weed density showed that when grouped into subcategories, studies involving relay cropping, coarse-textured and silt-dominated soils, and alkaline soils exhibited homogeneity, while all other subgroups displayed heterogeneity. According to the I2 statistic, the lowest heterogeneity was found in studies conducted on alkaline soils, whereas the highest heterogeneity occurred under conventional tillage (Table S2).

The meta-analysis of 15 studies (171 observations) demonstrated that, overall, relay and double-cropping systems significantly reduced weed density by 56% (95% CI = − 62% to − 49.9%) compared to sole cropping systems (Fig. 3B). This reduction was consistently significant across all environmental and management conditions evaluated, including variations in soil texture, salinity, irrigation regimes (rainfed and irrigated), and tillage practices, when compared to sole cropping (Fig. 3B). When considered separately, relay cropping and double cropping resulted in significant weed density reductions of 54% (95% CI = − 63.6% to − 44.6%), and 59.6% (95% CI = − 66.2% to − 52.9%), respectively, compared to sole cropping. Although double cropping appeared slightly more effective than relay cropping, the difference between the two systems was not statistically significant (Fig. 3B).

In relation to soil pH, the studies conducted in alkaline soils showed a 26.4% (95% CI = − 5.6% to − 47%) reduction in weed density under relay and double-cropping systems, while those in neutral soils exhibited a 63% reduction. This difference was statistically significant, indicating that these cropping systems were more effective in neutral soils than in alkaline soils (Fig. 3B). The analysis of soil texture also revealed significant reductions in weed density associated with relay and double-cropping systems. Weed density reduction varied by soil texture, with the greatest suppression in silt-dominated (58.30%) and medium-textured soils (54.69%), and a more moderate reduction in coarse-textured soils (31.74%) (Fig. 3B).

Regarding tillage systems, both conventional tillage and no-till significantly reduced weed density by 69.5% (95% CI = − 75.8% to − 63%), and 66.9% (95% CI = − 75.8% to − 58%), respectively, relative to sole cropping. The difference between the two tillage methods was not statistically significant (Fig. 3B).

In saline soils, the implementation of relay and double-cropping systems resulted in a 66.9% (95% CI = − 75.2% to − 58.6% ) reduction in weed density compared to sole cropping. Under rainfed conditions, the reduction was 63.34% (95% CI = − 70% to − 56.7%), while under irrigated conditions, it was only 39.21% (95% CI = − 39.2% to − 22.4%). As shown in Fig. 3, the difference between rainfed and irrigated conditions was statistically significant, demonstrating the superior weed suppression potential of these systems under water-limited conditions.

Weed count

A total of eight studies were included in the meta-analysis to assess the effect of relay cropping and double-cropping systems on weed count. Following study categorization, the heterogeneity analysis indicated that only the data from relay cropping studies were homogeneous, while all other groups exhibited heterogeneity. The lowest and highest levels of heterogeneity, as indicated by the I2 statistic, were observed in the relay cropping and no-tillage systems, respectively (Table S3).

Overall, the implementation of relay cropping and double-cropping systems resulted in a significant 47.60% (95% CI = − 56.6% to − 38.7%) reduction in weed count compared to monocropping (Fig. 3C). These systems consistently reduced weed numbers under all examined conditions, except in acidic soils, where the reduction (13.8%) was not statistically significant.

Separate meta-analyses of relay and double cropping demonstrated significant reductions in weed counts of 39% and 49%, respectively, relative to monoculture. Although the reduction was slightly greater with double cropping, the difference between the two systems was not statistically significant.

The impact of tillage practices on weed count was also evaluated. Conventional tillage and no-tillage systems each showed significant reductions in weed count by 36.36% and 63.48%, respectively, compared to monocropping. These two tillage systems also differed significantly from one another. Further analysis of studies conducted under specific environmental and soil conditions revealed significant reductions in weed counts when relay and double-cropping systems were applied in rainfed environments (37% reduction), irrigated systems (65% reduction), and coarse-textured soils (35% reduction).

These findings confirm that the weed-suppressive effects of relay and double-cropping systems are more pronounced under rainfed conditions than under irrigation (Fig. 3C).

Weed species richness

To assess the impact of relay and double-cropping systems on weed species richness, a total of seven studies (45 observations) were included in the meta-analysis. Weed species richness presented moderate heterogeneity, with a significant Q under the fixed-effect model (Q = 85.57; p < 0.01) and relatively low I2 under the random-effects model (10.67%) (Table 2). After categorizing the studies, the homogeneity analysis revealed that all groupings, except for relay cropping and neutral pH soils, exhibited heterogeneity. Among the evaluated groups, data from double cropping and neutral pH soils showed the highest and lowest levels of heterogeneity, respectively, based on the I2 statistic (Table S4).

Overall, the application of relay and double-cropping systems resulted in a non-significant 5% (95% CI = − 11.7% to -22.3%) reduction in weed species richness. Separate meta-analyses for relay and double cropping also showed non-significant reductions in weed species richness, by 11% and 6%, respectively. There was no statistically significant difference between the effects of the two cropping systems.

The analysis of tillage systems indicated that conventional tillage led to a non-significant 32% (95% CI = − 22.3% to − 11.7%) reduction in weed species richness, while no-tillage caused a significant 16% increase in richness (Fig. 3D). This increase may be attributed to more favorable conditions for a greater variety of weed species to germinate in the absence of tillage. It may be inferred that the increased weed species richness introduced through relay or double-cropping systems could also contribute to increased weed diversity.

Analysis of soil texture types revealed that in coarse-textured soils, the use of relay and double cropping significantly increased weed species richness by 49% (95% CI = − 84.4% to -15%) compared to monoculture. In contrast, in silt-dominated soils weed diversity was significantly reduced by 19.8% (95% CI = − 3% to − 36.7%) under these cropping systems.

Because the studies conducted on acidic soils overlapped with those in texture group A, similar results were obtained for both categories. Additional findings from studies conducted in rainfed conditions and on neutral pH soils showed that the application of relay and double-cropping systems resulted in a non-significant 4% (95% CI = − 23.5% to − 15%) reduction and a significant 31.2% (95% CI = − 45.2% to − 17.3%) reduction, respectively, in weed species richness compared to monoculture systems.

Crop biomass

Crop biomass showed high heterogeneity, with a Q value of 1259.29 (fixed-effect) and 374.88 (random-effect), both statistically significant at p < 0.01. The corresponding I2 values (87.93% and 59.45%) suggested that a large portion of the variation in crop biomass responses was due to real differences among studies rather than sampling error alone (Table 2). When categorizing the studies on plant biomass into different groups, it was observed that all studies exhibited heterogeneity except those conducted on non-saline soils and fine-textured soils. The lowest and highest heterogeneity, based on the I2 statistic, were found in studies with fine-textured and silt-dominated soils, respectively (see Table S5).

The meta-analysis of the studies showed that, overall, relay and double-cropping systems had a statistically significant positive effect of 34.8% (95% CI = 20.7% to 49%) on plant biomass compared to monocropping systems. However, no significant effect on plant biomass was observed in studies conducted on alkaline soils, soil texture C, no-tillage systems, or under irrigated conditions relative to monocropping (Fig. 4A).

Fig. 4.

Fig. 4

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Estimated percentage changes in two crop-related traits including (A) crop biomass and (B) crop yield under relay cropping and double cropping systems compared to sole cropping (monoculture). The panels show meta-analysis results for: crop yield and crop biomass. Changes are grouped by experimental conditions, including cropping system, irrigation type, tillage system, soil salinity, soil pH, and soil texture. Error bars represent 95% confidence intervals. Soil textures are coarse-textured soils (Soil_a), silt-dominated soils (Soil_b), medium-textured soils (Soil_c), and fine-textured soils (Soil_d).

Further analysis revealed that double and relay-cropping systems significantly increased plant biomass by 42% (95% CI = 16% to 69%) and 35.84% (95% CI = 18.4% to 53.3%), respectively, compared to monocropping. Regarding soil pH, the use of relay and double-cropping systems in acidic soils and neutral soils resulted in biomass increases of 90.5% (95% CI = 45.6% to 135.35%) and 146.6% (95% CI = 97.7% to 195.4%), respectively, over monocropping systems. These two cropping systems did not differ significantly from each other in performance under acidic and neutral soil conditions (Fig. 4A).

The results also indicated that both cropping systems performed better under rainfed conditions than under irrigation. Specifically, in rainfed areas, relay and double-cropping systems increased plant biomass by 31.65% relative to monocropping, which was statistically significant. In contrast, under irrigated conditions, these systems did not produce a significant effect on biomass (Fig. 4A).

Examination of tillage systems showed that conventional tillage combined with relay and double cropping resulted in a significant positive effect on plant biomass compared to monocropping, whereas no-tillage did not produce such an effect. Regarding soil texture, the use of relay and double-cropping systems significantly increased plant biomass by 85% (95% CI = 50.9% to 120%), 34% (95% CI = 4.9% to 64.8%), and 124% (95% CI = 101.3% to 147.4%) in coarse-textured, silt-dominated, and fine-textured soils, respectively, compared to monocropping (Fig. 4A).

Crop yield

Overall, the meta-analysis on the yield trait included 40 studies comprising 256 observations. The Q statistic was not significant under either model (Q = 284.79 fixed; 229.53 random), and the I2 under the random-effects model was 0.00%, indicating no meaningful heterogeneity among studies for this trait (Table 2). When categorizing the studies into different groups, it was observed that data from relay cropping, rainfed systems, and acidic soils exhibited significant heterogeneity, whereas data from other groups showed homogeneity, as presented in Table S6. Additionally, the lowest and highest heterogeneity, based on the I2 statistic, were found in alkaline and acidic soils, respectively (Table S6).

The meta-analysis results from these 40 studies indicated that, in general, the use of relay and double-cropping systems led to a significant 11% (95% CI = − 16.8% to − 6.2%) reduction in crop yield compared to monoculture systems. However, a more detailed analysis showed that relay cropping did not significantly reduce yield, with an estimated decline of 6% (95% CI − 17% to 3.47%), whereas double cropping caused a significant yield reduction of 16% (95% CI − 22.3% to − 10.3%) relative to monoculture (Fig. 4B).

The effects of two tillage systems—conventional tillage and no-tillage—on yield were also evaluated. These systems differed significantly, with conventional tillage causing a significant decrease and no-tillage causing a significant increase in yield compared to monoculture. The combined results revealed that relay and double-cropping systems under no-tillage improved yield by 49% (95% CI = 33.4% to 64.9%) relative to monoculture, whereas the same cropping systems under conventional tillage reduced yield by 20% (95% CI = − 26.37% to − 14.32%) (Fig. 4B).

The present study also found that relay and double-cropping systems in saline, non-saline soils, and soils with acidic or neutral pH did not significantly affect yield compared to monoculture. However, the meta-analysis in alkaline soils revealed a significant negative effect, indicating yield reductions.

Under rainfed conditions, the use of relay and double-cropping systems did not result in significant differences in crop yield compared to monoculture. This suggests that these systems help maintain yields, particularly under drought and water-limited conditions.

An examination of soil texture showed that relay and double-cropping systems reduced yield by 12% (95% CI = − 21.6% to − 3%) in silt-dominated soils, 15% (95% CI = − 24.4% to − 6.5%) in medium-textured soils, and 5% in coarse-textured soils, with no significant differences observed between silt-dominated and medium-textured soils (Fig. 4B).

Discussion

Weed suppression and yield trade-offs in relay and double-cropping systems

This meta-analysis confirmed substantial heterogeneity among studies evaluating relay and double-cropping systems, underscoring the need for subgroup analyses to identify context-specific drivers of variation in weed and crop responses. These findings established that diversified cropping systems are highly effective for ecological weed management across variable conditions; however, enhancing or maintaining crop performance is system-specific, favoring relay cropping over double cropping due to the latter’s yield penalty.

Relay and double-cropping systems play an important role in reducing weed pressure by limiting the space and resources availability for weed growth, for example in relay cropping, sequential planting results in more continuous crop cover, suppressing weed emergence by shading the soil surface and reducing light availability9,10. Double cropping maximizes land use intensity within a single agricultural year, thereby reducing the time available for weed establishment between successive crop cycles23,30. In addition, higher crop density and faster canopy closure in these systems reduce weed competition for nutrients, water, and light5,9,10. These conclusions are supported by numerous empirical studies. For example, Qayyum et al.64 demonstrated that relay intercropping wheat with oilseed crops significantly increased biological and grain yields while reducing weed biomass and density. Mixed cropping with strategic row arrangements decreased weed proliferation relative to monoculture wheat plots. Similarly, São Miguel et al.69 highlighted the benefits of cover crops in double-cropping systems, demonstrating that the inclusion of cover crops effectively suppresses weed growth and reduces the weed seed bank. In contrast, periods of fallow without cover crops were shown to be less effective in controlling weeds, often leading to increased seed bank accumulation. Additionally, their research indicated that conventional tillage practices stimulate off-season weed germination by disturbing the soil, thereby exacerbating future weed infestations. Environmental factors such as temperature and precipitation further modulate weed communities. São Miguel et al.69 reported that increased rainfall stimulated germination of certain weed species like Digitaria horizontalis, while others remained dormant. Cover cropping in intercropping systems may delay weed germination until favorable conditions arise, contributing to weed suppression through temporal niche manipulation80.

When comparing relay and double cropping, each system presents distinct advantages and trade-offs. Relay cropping, which involves staggered planting where the second crop is sown before the first is harvested, can better utilize residual resources and maximize the use of the available growing season, often with less intense interspecific competition81. Our meta-analysis showed that relay cropping led to an insignificant yield reduction compared to monoculture, while double cropping resulted in a significant yield decrease. This suggests that relay cropping may better maintain crop productivity while delivering some of the benefits of crop intensification82.

However, interspecific competition can negatively affect yield depending on crop combinations and management. For example, Qayyum et al. reported that in a wheat–sunflower intercropping system, the highest wheat grain yield was obtained in single-row wheat monoculture, whereas the lowest wheat yield was observed in a three-row wheat–sunflower intercropping arrangement64. Similarly, Vrignon-Brenas et al.75 found no significant yield differences between relay and double-cropping systems, though protein content was lower in double cropping. This risk of yield reduction was also highlighted by Wanic et al.83, who identified competition for light and nutrients as a key drawback of companion cover crops.

The spatial configuration of crops also influences weed suppression and productivity. The use of cover crops in double-cropped systems provides strong weed suppression under Mediterranean irrigated conditions.84 Their study demonstrated that winter cover crops, particularly rye, significantly reduced weed biomass in the subsequent soybean crop when sufficient biomass was achieved before termination. Weed control effectiveness can also be influenced by the ability of cover crops to establish quickly and form a dense canopy. Furthermore, they noted that in double-cropped systems, strategic use of cover crops can mitigate the negative effects of fallow periods by reducing seed bank replenishment and off-season weed emergence. These findings underscore the importance of integrating ecological management tools, such as cover crops, into intensified cropping systems to enhance weed suppression while promoting sustainable agricultural practices. Leoni et al.10 found that appropriate relay intercropping of legumes reduced weed biomass by up to 90% during cropping and 94% in the following spring, though some legumes may increase weed biomass in the subsequent season depending on species and management.

Our meta-analysis found that no-tillage systems increased yield by nearly 49% compared to monoculture systems, whereas conventional tillage was linked to yield reductions. These results underscore a key agronomic trade-off: while no-till systems can boost yields by fostering soil health85,86. Although conventional tillage may initially result in higher crop yields in the short term compared to no-till systems, it is frequently linked to yield reductions in the long run due to progressive soil degradation85. Conservation tillage or no-tillage generally performed better than conventional tillage in enhancing crop yields, particularly in combination with diversified cropping systems. Conservation tillage improves moisture retention, soil structure, and biotic activity86,87, while conventional tillage can potentially increase erosion and disrupts soil aggregates, depending heavily on site-specific factors such as climate, topography, and soil type87.

The influence of soil pH and texture was also notable. Acidic soils were associated with more pronounced yield reductions, likely due to nutrient limitations and toxicities88, while neutral and alkaline soils provided better conditions for nutrient uptake and root growth. Soil texture influenced performance as well; loamy and silty soils showed greater yield reductions under mixed cropping than sandy or clayey soils, possibly due to differences in water retention and nutrient availability. Soil texture significantly impacts water retention and nutrient availability. Silty soils, with their fine particles, have a higher water-holding capacity than sandy soils, which can benefit crops during dry periods. However, they may also be prone to compaction, affecting root growth. Clay soils, while retaining water and nutrients well, can become waterlogged, leading to root oxygen deprivation. Sandy soils drain quickly and have lower nutrient-holding capacities, which can lead to nutrient leaching but may reduce the risk of waterlogging. Loamy soils, being a balanced mixture of sand, silt, and clay, are generally considered ideal for agriculture due to their favorable water retention and nutrient availability89.

Moisture regime played a role in the effectiveness of these systems. Relay and double-cropping systems performed similarly under rainfed conditions without significant yield penalties. This suggests their value in water-limited environments, likely through improved soil cover and moisture conservation. However, under irrigated conditions, benefits were less consistent, possibly due to altered competition dynamics and water use efficiency. These findings are consistent with broader evidence suggesting that mixed cropping systems can maintain or enhance productivity under drought stress by improving resource use efficiency and modifying the microclimate90.

Despite variability, the potential of relay and double-cropping systems for broad agroecological applications is well documented. Examples of relay cropping include wheat-potato91, rice-chickpea92, red clover-wheat93, legumes-millet94, and legumes-maize systems95. In addition, Latati et al.96 found that wheat-chickpea intercropping significantly improved biomass, grain yield, and nitrogen uptake by 48%, 44%, and 30%, respectively, compared to monoculture.

Challenges and future directions for weed control in relay and double-cropping systems

Despite the demonstrated benefits of relay and double-cropping systems for weed suppression, several limitations constrain their broader adoption and consistent effectiveness across regions. One key challenge is the context-dependent nature of weed control outcomes, which vary with crop species combinations, management practices, climatic conditions, and soil properties. As indicated by the high between-study heterogeneity and wide prediction intervals in our meta-analysis, optimizing competitive interactions requires site-specific adaptation and careful species selection.

Another limitation is the complexity of management for these systems. Relay cropping, demands precise timing and coordination of planting and harvesting operations to avoid overlapping resource competition or labor bottlenecks5,97. Likewise, double cropping requires suitable growing seasons and sufficient resource availability (e.g., water and nutrients), which may not be feasible in regions with short or erratic growing periods98. These technical and logistical constraints can limit adoption, especially for smallholder farmers or in areas with limited access to inputs and machinery.

Additionally, although substantial research exists in these areas, the complex long-term effects of intensified cropping on soil nutrient dynamics, pest populations, and crop health still warrant further systematic evaluation. While weed suppression is often improved, there is a risk of increased interspecific competition leading to yield penalties, as observed in some intercropping configurations64,81. Continuous cropping may also accelerate the evolution of weed species with greater competitive ability or altered phenology, requiring adaptive management strategies99.

Future research should focus on integrating cropping system design with predictive modeling tools to guide context-appropriate decisions on crop combinations, sowing dates, and both crop and weed densities. Improved decision support systems (DSS), informed by local weather, soil, and weed dynamics, could enhance the reliability and scalability of these cropping systems. There is also a need for long-term, multi-site trials to evaluate the cumulative agronomic and ecological effects of relay and double cropping, including their interactions with conservation practices such as reduced tillage and organic amendments.

Furthermore, a crucial next step is to identify crop traits that confer compatibility and competitive advantage in mixed systems—such as shade tolerance, altered root architecture, early vigor, and rapid canopy closure—as trait identification is typically a prerequisite for targeted breeding. Prioritizing these traits could lay the groundwork for developing varieties better suited to mixed systems, thereby enhancing weed suppression while maintaining or improving yields.

Towards a paradigm shift in cropping strategies

Our meta-analysis of the available data clearly illuminates an important tradeoff at the core of agricultural intensification: the strategic tradeoff of relay cropping’s weed-suppressive resilience versus the yield potential of double cropping. The data shows that although relay cropping acts as a biological weed management tool and can often reduce weed biomass significantly (e.g. on average by 45%), there is often a temporary reduction in terms of the main crop yield that is incurred from using relay cropping. In contrast, double cropping maximizes yield during the immediate season, but remains fundamentally susceptible to the intense weed pressure that may occur during the following crop season and that may require significant additional input to manage.

This will not only be a critical technical distinction between two cropping practices, but it also represents a critical decision point that determines a cropping system’s long-term sustainability, ecological footprint, and profitability. For practitioners and agronomists, this finding demonstrates that there is no single solution for agriculture-related problems. The implementation of intensified cropping systems must be based on the specific circumstances within each cropping system, and in some situations, relay cropping may provide sound ecological benefits in areas with significant herbicide-resistant weed populations or areas where the reduction of chemical inputs will be a high priority. In other situations (such as regions with longer growing seasons and higher market demands), double cropping can continue to be a financially viable option, but only if supported by appropriate integrated weed management (IWM) systems to minimize future weed-related challenges.

Conclusions

This meta-analysis demonstrated that relay and double cropping are potent strategies for ecological weed management, reducing weed biomass by approximately 78% and 95%, respectively, across diverse environmental conditions. However, their effect on crop productivity is system-dependent: double cropping revealed a significant yield penalty, whereas relay cropping showed substantial weed suppression without a significant yield loss. Therefore, relay cropping may represent a promising pathway within the scope of the yield and weed metrics analyzed here.

The success of these systems is context-dependent, influenced by crop combinations and management practices. While both systems introduce logistical complexity, the significant yield constraint in double cropping highlights a critical trade-off not present in relay cropping. Consequently, adoption should prioritize adaptive, site-specific planning, where relay cropping can serve as a competitive alternative to monoculture, particularly regarding weed suppression and yield optimization.

Future research must focus on optimizing relay systems through breeding for crop compatibility and developing decision-support tools. As agriculture confronts challenges of herbicide resistance and climate change, relay cropping offers a resilient pathway toward sustainable intensification, leveraging ecological principles for effective weed control while maintaining farm productivity.

Supplementary Information

Below is the link to the electronic supplementary material.

Supplementary Material 1 (48.5KB, docx)

Author contributions

Conceptualization: ES, FB. Methodology: ES. Data analysis: AK, ES. Writing—original draft: AK. Writing—review and editing: ES, FB. Supervision: ES, FB. Project administration: ES.

Funding

This research received no specific funding from funding organizations in the public, commercial or non-profit sectors.

Data availability

The datasets generated/analyzed during the current study are available in the [Zenodo] repository, [10.5281/zenodo.18514486].

Declarations

Competing interests

The authors declare no competing interests.

Ethical approval

No human or animal subjects were involved.

Consent to participate

This study was conducted on plants and did not involve human participation.

Consent for publication

This research did not involve any personal data requiring consent for publication.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplementary Material 1 (48.5KB, docx)

Data Availability Statement

The datasets generated/analyzed during the current study are available in the [Zenodo] repository, [10.5281/zenodo.18514486].

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