Crop Rotation and Diversification in China: Enhancing Sustainable Agriculture and Resilience

Abstract

Crop rotation and diversification (CRD) are crucial strategies in sustainable agriculture, offering multiple benefits to both farmers and the environment. By alternating crops or introducing diverse plant species, CRD practices improve soil fertility, reduce pest populations, and enhance nutrient availability. For example, legume-based rotations increase soil nitrogen levels through biological nitrogen fixation, reducing the need for synthetic fertilizers. Moreover, these practices promote more efficient water and nutrient use, reducing the reliance on synthetic fertilizers and minimizing the risk of pests and diseases. This review synthesizes findings from recent research on the role of CRD in enhancing sustainable agriculture and resilience, highlighting the potential contributions of these practices towards climate change mitigation and adaptation. Specific crop rotation systems, such as the cereal–legume rotation in temperate regions and the intercropping of maize with beans in tropical environments, are reviewed to provide a comprehensive understanding of their applicability in different agroecological contexts. The review also addresses the challenges related to implementing CRD practices, such as market demand and knowledge transfer, and suggests potential solutions to encourage broader adoption. Lastly, the potential environmental benefits, including carbon sequestration and reduced greenhouse gas emissions, are discussed, highlighting the role of CRD in building resilient agricultural systems. Collectively, this review paper emphasizes the importance of CRD methods as sustainable agricultural practices and provides key insights for researchers and farmers to effectively integrate these practices into farming systems.

1. Introduction

The rapidly increasing global population, coupled with changing climatic conditions, continues to pose substantial challenges to global food production and security [1]. Achieving sustainable and resilient agricultural systems has become an utmost priority for ensuring long-term food availability, maintaining ecosystem services, and minimizing adverse environmental impacts [2,3]. To address these challenges, scientists, policymakers, and farmers alike have increasingly turned to alternative farming practices such as crop rotation and diversification (CRD) [4,5,6].

Historically, a significant proportion of the world’s agricultural systems has relied on monocultures, which involve in the continuous cultivation of a single crop species on a given piece of land [7]. While monocultures can allow for efficient production of high-yielding crops, they often trigger the cost of reduced soil health, reliance on synthetic inputs, and increased vulnerability to pests, diseases, and climate extremes [8,9,10]. Acknowledging the limitations and risks associated with monocultures, there has been a growing realization of the potential benefits of implementing diverse and dynamic farming systems [11,12].

Crop rotation, a time-honored agricultural practice, involves alternating the cultivation of different crops in a defined sequence over a specific period within a defined area [13]. By rotating crops, farmers reduce the risk of the buildup of pests, diseases, and weeds specifically adapted to a particular crop [14,15]. Furthermore, such systems can enhance soil fertility by incorporating nitrogen fixers, deep-rooted plants, or cover crops into the rotation, consequently reducing the reliance on synthetic fertilizers [16,17]. Intercropping systems, which consist of growing two or more crops simultaneously in close proximity, can create a synergistic relationship between different species, leading to increased yields, reduced pest pressure, and enhanced resource use efficiency [17]. Such systems maximize niche utilization and minimize resource competition, ultimately promoting more sustainable agricultural production.

In addition to crop rotation, the diversification of agricultural landscapes also plays a crucial role in enhancing the sustainability and resilience of farming systems [17]. The introduction of multiple crops, including cash crops, food crops, and cover crops, within a farming system can alleviate economic risks, improve nutritional diversity, and enhance ecosystem services [18]. Diversification can reduce the dependence on a single crop for income generation, spreading risks associated with market volatility and price fluctuations. Moreover, incorporating diversified cropping systems can enhance dietary diversity and address nutritional deficiencies within local communities [19].

In recent years, mounting evidence has indicated the potential of CRD practices as crucial strategies in promoting agricultural sustainability and resilience [11,17,20,21]. These practices have been linked to reduced chemical inputs, increased biodiversity, and habitat preservation and enhanced adaptive capacity to climate change impacts. Despite these positive outcomes, significant challenges remain in adopting these practices, including economic constraints, knowledge gaps, and resistance to change.

In this review, we aim to explore the current understanding of the benefits and challenges associated with CRD practices in enhancing agricultural sustainability and resilience. We will provide six insights into potential benefits of CRD, including soil fertility, climate change, weed suppression, yield, and pest and disease management. Furthermore, we will discuss future research priorities and potential policy interventions required to facilitate widespread adoption of these practices for global sustainable agriculture. By examining the existing knowledge, key challenges, and pathways for implementation, we anticipate that this review will contribute to advancing our understanding of sustainable agricultural solutions, aiding farmers and researchers in making informed decisions to address these critical challenges and pave the way for a more sustainable and resilient agricultural sector.

2. Benefits of CRD: Enhanced Soil Fertility Management

CRD practices are widely recognized as effective strategies for managing soil fertility in agricultural systems [17,18]. Soil fertility is crucial for maintaining agricultural productivity. Continuous monocropping has significantly depleted soil nutrients and promoted the buildup of crop-specific pests and diseases. CRD practices offer a solution to these challenges by effectively managing soil fertility and disturbing their life cycles [21]. When different crops are introduced into a rotation, their varying nutrient demands and rooting patterns help reduce the risk of nutrient imbalances and enhance overall nutrient cycling.

The principle of increasing functional diversity in crop rotations, rather than just species diversity, has been found to be more predictive of the impact on soil organic matter (SOM) concentrations. For instance, rotations that include cover crops or perennial species can significantly increase carbon input to the soil and SOM concentrations. This is because crop rotations take advantage of temporal niches that would otherwise be unproductive, thereby enhancing the “perenniality” of the agricultural system [22]. Similarly, intercropped systems had grain yields that were on average 22% greater than monocultures, with greater year-to-year stability. This increase in yield was attributed to observed increases in SOM, total nitrogen, and macroaggregates in intercropped soils compared to monoculture soils [11].

The mechanisms underlying these benefits are multifaceted and involve complex interactions between plant roots, soil microorganisms, and soil physicochemical properties. CRD practices promote nutrient cycling by introducing different plant species with varying nutrient requirements and root systems, which promote nutrient cycling by altering the root exudates, root biomass deposition, and residue quality [16,23]. Different crops have unique root exudates that influence the soil microbial community composition and nutrient cycling in the rhizosphere. For example, leguminous crops, such as soybeans or peas, have the ability to fix atmospheric nitrogen through symbiotic relationships with nitrogen-fixing rhizobia bacteria [23,24]. When these crops are included in the rotation, they enrich the soil with nitrogen, benefiting subsequent non-legume crops, while in phosphorus-limited soils, non-legume diversification may be more beneficial. The use of low carbon-to-nitrogen organic residues and greater temporal diversity in cropping sequences can significantly increase soil carbon and nitrogen retention [25]. This has profound implications for regional and global carbon and nitrogen budgets, as well as for sustained production and environmental quality.

Similarly, rotations that include sweet potato or spring peanut can enhance soil organic carbon, total nitrogen, available phosphorus, and enzyme activities, which are indicative of improved soil health [26]. Crop residues from different species decompose at different rates, providing a continuous supply of nutrients throughout the growing season [27]. In a practical agricultural context, rotations involving cassava, pigeon pea, and Mucuna have significantly increased subsequent maize yields [28]. This was attributed to the faster decomposition and nutrient release from the biomass of these crops compared to poorer quality residues like maize stover.

Long-term field trials in Norway revealed that different crop rotations and fertilization systems had small effects on yield and soil fertility parameters, with a slight decrease in soil organic carbon (SOC) and an increase in soil nitrogen over time [29]. However, a study on alluvial soils found that crop rotation systems improved soil organic carbon, total nitrogen, and available phosphorus, with maize–mung bean and mung bean–chili rotations showing the most significant improvements [30]. This suggests that the benefits of crop rotation may be more pronounced in the context of specific soil types and environmental conditions.

The importance of soil biota in the design of crop rotations is highlighted by Dias et al. [31], who emphasizes that optimizing plant–soil microbial interactions can lead to improved crop productivity and soil health. This is because diverse rotations can reduce the load of pests and pathogens and promote beneficial microbial communities that contribute to nutrient cycling and soil structure. The most diverse rotations led to the most metabolically diverse and active soil microbial community, which, in turn, was associated with higher plant biomass production and soil pH, indicating a positive feedback loop between crop diversity, microbial activity, and soil fertility [32].

Different crops with varying root systems apply diverse levels of mechanical stress on the soil, which enhances soil structure and its ability to retain water. This allows for the utilization of soil nutrients throughout the entire rooting zone, improving nutrient use efficiency and reducing soil nutrient losses due to leaching [33]. Crops with deep taproots, such as alfalfa or certain cover crops, can access deep soil layers and extract nutrients that would otherwise remain untapped, benefiting subsequent crops grown in the same soil [34]. For example, the depth of the roots is directly related to the efficiency of ${\mathrm{N}\mathrm{O}}_3^{-}$ uptake, with deeper roots being able to access and recycle nitrogen that has leached to deeper layers, thus improving nitrogen use efficiency in crop rotations [35]. The deep roots and associated rhizospheres of these plants can induce weathering of primary minerals in the soil, releasing nutrients that are essential for plant growth. This process not only contributes to the nutrient supply for the plants but also results in carbon transfer to the soil, which can be beneficial for soil health and structure [36]. Particularly, the taproot systems of perennial legumes have been shown to increase the density of vertical biopores, which are tubular-shaped continuous soil pores formed by plant roots and earthworms. These biopores make the subsoil layers more accessible for succeeding crops, enhancing the nutrient uptake from these deeper layers. Additionally, the activity of anecic earthworms, which is increased by the presence of deep roots and organic matter, can further improve the structure of the soil and create a favorable environment for root growth and nutrient uptake [37]. Otherwise, shallow-rooted crops, such as vegetables and cereals, expand horizontally, improving soil aggregation and water retention [38]. The development of the root exodermis, which is a protective layer in some plant species, can influence water retention in the soil. Root segments from species with an exodermis, such as maize and sorghum, show higher water retention compared to those without this feature, like wheat [39]. The exodermis can act as a barrier against water loss from roots back into the soil, which is particularly important in dry or saline areas [39]. Additionally, the formation of soil sheaths around roots in very dry soil can further prevent water loss, suggesting that, in some cases, the physical interaction between roots and soil can be more effective than the biological structures of the roots themselves. Crop diversification fosters a diverse root system network that collectively enhances soil structure, promoting root growth and water infiltration. Furthermore, the introduction of cover crops in a rotation contributes to soil health by providing ground cover, preventing nutrient leaching, and mitigating soil temperature fluctuations. Cover crops add organic matter to the soil through biomass incorporation, further improving soil fertility and structure.

In conclusion, CRD practices play a pivotal role in promoting SOM accumulation, thereby enhancing soil fertility, improving soil structure, facilitating nutrient cycling, fostering a diverse soil microbial community, and reducing soil erosion. The diverse root systems of different crops can modify the soil’s physical properties, such as compaction and porosity, as well as enhance the soil’s capacity to retain water through the development of structures like the exodermis and the alteration of soil organic matter and structure. These practices are essential for maintaining agricultural sustainability and ensuring the long-term health and productivity of soils (Figure 1).

3. Increased Mitigation and Resilience to Climate Change by CRD

Climate change is one of the greatest challenges that the world is currently facing, with severe implications for global food production. Agriculture plays a dual role in climate change: it is both a victim of its impacts and a contributor to climate change, with the sector’s current practices leading to approximately 11% of total anthropogenic greenhouse gas (GHG) emissions [40]. On the one hand, the increasing frequency and intensity of extreme weather events, such as droughts, floods, and heatwaves, pose significant risks to agricultural systems. On the other hand, the extensive use of nitrogen-based fertilizers in monoculture is a significant source of nitrous oxide (N₂O) emissions [41]. N₂O, a potent GHG with a global warming potential nearly 300 times that of CO₂, is emitted through nitrification and denitrification processes in soils [42,43]. Additionally, livestock production, rice cultivation, soil management, land use change, and energy consumption in agriculture are all significant contributors to GHG emissions [42,43,44,45].

CRD practices are agricultural management strategies that contribute significantly to the mitigation of GHG emissions (Figure 1). They not only mitigate GHG emissions through various direct and indirect mechanisms such as increased carbon sequestration, efficient nutrient management, reduced synthetic inputs, and improved soil health, but also through less tangible means, such as influencing volatile organic compound emissions and legacy soil effects [41,46,47,48]. Intercropping systems, such as mixed intercropping of cowpea and melon, can enhance land productivity and reduce the reliance on synthetic fertilizers. This results in a decrease in emissions per unit of product, which is a direct way to control GHG emissions [46,49]. Integrating biofuel crops such as switchgrass into crop rotation can enhance soil carbon sequestration and impact the annual CO₂ flux in the cultivation environment. The proper management of nitrogen fertilizer is crucial to minimize N₂O emissions in such systems [47]. Crop rotation that incorporates perennial plants, like fruit orchards, can also act as efficient sinks for atmospheric carbon, aiding in the minimization of emissions caused by field crops through soil disturbance and the release of GHGs [50]. Additionally, innovative technologies in digital agriculture, crop genetics, and electrification, combined with CRD, have the potential to reduce GHG emissions from row crop agriculture significantly, helping to achieve net negative emissions while maintaining productivity [51]. During the corn crop of the rotation, with high fertilization rates, agroforestry reduced soil N₂O emissions by 9% to 56% compared to monocultures [41]. Crop rotation with catch or cover crops has been shown to play a significant role in GHG emission mitigation. These crops can enhance carbon storage not only in their above-ground biomass but also in their below-ground biomass [52]. By enhancing the soil’s organic carbon content, cover crops improve soil structure and function, leading to greater resistance against erosion and nutrient loss, which further mitigates GHG emissions.

The relationship between crop yields and GHG emissions is complex and influenced by various agricultural practices. Biochar application emerges as a promising strategy to reduce GHG emissions (CH4 by −37%, N₂O by −25%, CO₂ by −5%) while enhancing crop productivity, particularly for wheat [53]. However, practices like no-tillage and manure application may increase GHG emissions, with the latter still boosting crop yields [53]. Improving productivity through agronomic changes, intercropping, and efficient nitrogen use can lead to reductions in GHG emissions. The impact of nitrogen fertilization on GHG emissions is significant, and its management is crucial for sustainable biomass production [54,55]. Correlations between soil properties and GHG emissions highlight the importance of soil health in agricultural sustainability [56]. Overall, a balance between increasing productivity and reducing GHG emissions is essential for achieving both food security and environmental protection.

CRD practices are pivotal strategies for enhancing agricultural resilience to climate change by providing a buffer against unpredictable weather patterns, pests, and diseases that climate change may exacerbate. Diversified crop rotations have has evolved to mitigate the effects of weather variations and improve yield stability, which is crucial in the face of unpredictable environmental stresses [57]. The introduction of a variety of crops, including legumes and small grains, into rotations can significantly increase yield stability, particularly under abnormal weather conditions such as hot and dry years [57,58]. Similarity, the short-term effects of crop diversity on resilience and ecosystem service provision under drought have been positive. Increased crop diversity has been found to maintain yields with reduced external inputs under varying climatic conditions and improve stress resistance, resulting in more resilient systems [58].

The benefits of crop rotation on climate resilience are not limited to short-term gains. Long-term studies have demonstrated that more diverse rotations can increase maize yields over time and across various growing conditions, including during droughts, thereby reducing yield losses [59]. Crop diversity, on a national scale, has also been suggested as an adaptive measure to cope with negative climate impacts, with evidence indicating higher yields for cereals in diverse rotations compared to monocultures, especially under high temperatures and low precipitation [60]. In China, where continuous cropping has become more popular due to high economic benefits, the importance of crop rotation for improving climate resilience has become increasingly clear. Crop rotation is seen as an essential tool for enhancing the resilience of agricultural production systems and effectively addressing the shortcomings of continuous cropping methods [61]. Crop diversification has also been found to improve system robustness by enhancing resistance to biotic stresses and maintaining consistent crop productivity across rotation cycles [62]. SOM, which is positively correlated with crop rotation diversification, plays a role in reducing water stress and yield losses due to drought [63]. Furthermore, crop residues and increased SOM accumulation contribute to carbon sequestration and promoting climate resilience [64]. Long-term crop rotation experiments have demonstrated a significant increase in soil carbon stocks compared to continuous monoculture systems. The effects of residue management as well as tillage on soil carbon sequestration in a wheat–corn double-cropping system indicate that no-tillage with residue management can increase SOM and is the most effective in enhancing soil carbon sequestration, despite the potential for increased CO₂ efflux [53,65]. Diversifying traditional cereal monocultures (wheat–maize) with cash crops (sweet potato) and legumes (peanut and soybean) in the North China lain increased equivalent yield by up to 38%, reduced N₂O emissions by 39%, and improved soil health [33]. These findings underscore the importance of CRD practices as adaptive strategies to ensure food security and agricultural sustainability in the face of climate change. In summary, CRD practices act as a buffer against climate variability and extreme events by improving soil health, moisture management, and pest and disease resistance, leading to more stable and resilient agricultural systems.

4. Weed Suppression and Soil Health by CRD

Weed suppression is essential to ensure crop success, as weeds compete with cultivated plants for nutrients, water, and sunlight. Crop rotation offers an effective strategy to reduce weed populations by disrupting their life cycles and minimizing their adaptation to specific environments. When crops with different growth habits, nutrient requirements, and weed susceptibility are alternated, weed emergence and reproduction can be significantly suppressed. A meta-analysis encompassing 54 studies across six continents found that diversifying crop rotations reduced weed density by 49%, although it did not significantly affect weed biomass [66]. This reduction in weed density is attributed to the increased variance in crop planting dates and the associated management practices that come with crop diversification. Notably, diversification was more effective under zero-tillage conditions, reducing weed density by 65% compared to 41% under tilled conditions. This study indicated that crop rotation interrupts the spread of weeds by altering the timing and intensity of management practices such as tillage or herbicide applications.

Another aspect of crop rotation is the strategic arrangement of crops to exploit weed-weed competition, which reduces weed seed banks by utilizing cultural practices like planting cover crops or fallow periods that prevent seed production and promote weed seed decomposition [67]. This approach offers a novel mechanism for sustainable weed management without additional inputs. Additionally, diversifying crop rotations with broadleaf crops, rye, sorghum, rice, sunflower, rape seed, wheat, and legumes provides opportunities to leverage natural weed suppression mechanisms, such as allelopathy and competition for resources [68]. Allelopathy refers to the process by which plants release biochemicals, known as allelochemicals, into the environment that can have inhibitory or stimulatory effects on neighboring organisms [69]. These crops can release allelochemicals that not only inhibit weed growth but also enhance soil microbial activity [70]. The specific mechanisms of action can vary widely, ranging from disruption of cell division to interference with photosynthesis or hormone regulation [71,72]. In agricultural settings, allelopathy can be both beneficial and detrimental. On the one hand, it can provide natural weed suppression, reducing the need for chemical herbicides. On the other hand, it may negatively affect the growth of desirable crops or beneficial non-crop species, leading to yield losses and reduced ecosystem services [73]. The challenge lies in understanding the physiological and ecological mechanisms of allelopathy to optimize its use in agriculture. Recent research has begun to unravel the genetic basis of allelopathy, identifying specific genes and proteins involved in the production, transport, and perception of allelochemicals [74,75,76,77], which has provided deeper insights into the effects of allelochemicals on cell structure, membrane permeability, oxidative systems, growth regulation, respiration, enzyme metabolism, photosynthesis, and nutrient uptake [69]. Interestingly, plants have evolved intricate signaling pathways to perceive and respond to allelochemicals. Genes involved in these pathways can include those related to hormone signaling, such as auxin, gibberellin, and abscisic acid (ABA) pathways, which modulate plant growth and development in response to allelopathic stress [78].

Intercropping, the practice of growing multiple crops in the same field simultaneously or in alternating rows, further disrupts weed growth. This intermingling of crops often results in the more efficient use of space and resources by the intercropped plants, which can outcompete weeds for sunlight, nutrients, and water, effectively suppressing their growth [68,79]. For example, the inclusion of grasses or highly competitive crops in rotations can suppress weed germination and growth due to shading and root competition. Intercropping can also enhance the suppression of weeds by improving the growth and reproductive capacity of the crops themselves. For instance, intercropping cassava and maize with fertilizer application resulted in the highest leaf area index and light interception, leading to better weed control and higher crop yields [80]. However, the specific patterns of intercropping influence the effectiveness of weed suppression, where different intercropping patterns, such as the ratio of safflower to bean, can have varying impacts on weed control and crop performance under both weedy and weed-free conditions [81]. This highlights the importance of selecting compatible intercrop combinations to achieve the desired level of weed management. Interestingly, the relationship between crop diversity and weed pressure is not always straightforward. Increased crop yield in mixtures was not solely due to increased weed suppression. This suggests that other ecological processes may be involved, and that crop–weed interactions are influenced by the context. [82]. Finally, CRD has been linked to the disease-suppressive capacity of soil microbiomes. A field experiment demonstrated that crop diversity influenced soil bacterial community composition and increased the abundance of disease suppressive functional groups [83]. This indicates that the composition of the microbial community may be more important than diversity for disease suppression.

In summary, weed suppression mediated by CRD practices contribute to soil health by reducing the need for herbicides. Fewer herbicide applications mean lower chemical loadings, reducing environmental pollution, and minimizing impacts on beneficial soil organisms. Moreover, by minimizing the competition from weeds, crops experience reduced stress, leading to improved overall plant productivity and better nutrient utilization. These long-term benefits ultimately enhance soil quality and contribute to sustainable agricultural practices (Figure 1).

5. The Impacts of CRD on Pest and Disease Management

Pests and diseases are critical factors that can affect plant health and quality, potentially causing yield gaps. Continuous monocropping provides favorable habitats for specific pests and pathogens, which can build up populations that are difficult to control. Traditional strategies aimed at controlling major biotic constraints affecting crop plants in intensive production systems include resistance breeding, timely sowing, and adequate use of fertilizers. However, climate change may modify the wheat disease spectrum, and pathogens or pests considered unimportant today may become new threats in the near future [84]. In recent years, the practices of CRD have gained renewed interest as sustainable strategies for pest and disease management in agricultural systems. By disturbing the established life cycles of pests and diseases, CRD prevents their accumulation to economically damaging levels. The egg-laying site of the pest becomes unsuitable once the host crop is rotated out, leading to a decrease in pest reproduction rates. Similarly, diseases that require a continuous host for spore dispersal are hindered when their host crop is absent in the next rotation cycle (Figure 2). Furthermore, diversification within the farming system can create barriers to pest movement and diminish the overall impact of pest outbreaks. Mixing crops with different growth habits and life cycles can create diverse habitats for beneficial organisms that help control pests [85]. Although management practices such as crop and cultivar selection, fungicide application, and removal of weeds and volunteer crop plants play a crucial role in this process [85]; the role of microorganisms in plant disease control is evident to be more significant [86]. The “crop rotation effect” is attributed to the action of naturally occurring resident antagonists that help manage soilborne pathogens [87]. By avoiding the cultivation of the same crop in the same field for more than one or two consecutive years, the inoculum potential of pathogens can be reduced below economic thresholds [87].

Long-term studies have demonstrated that certain crop rotations, such as those including canola or rapeseed, can reduce the severity of soilborne potato diseases and increase tuber yields [88]. The addition of cover crops such as winter rye has been shown to further reduce disease severity and improve tuber yield. However, the study also highlighted the limitations of 2-year rotations, as all rotations resulted in increasing levels of common scab and verticillium wilt over time.

6. Positive Effects of CRD on Yields

The benefits of crop rotation diversity, particularly in terms of grain yield, are observed to increase over time [89]. Short-term grain yield benefits are seen after five years of implementation, with significant increases in yield observed up to 35 years post-implementation. These yield improvements are attributed to the ecological interactions and resource complementarity within diversified rotations, rather than technological advances [89].

The agronomic and ecological mechanisms contributing to CRD benefits include enhanced soil microbial activity and improved nutrient cycling and niche complementarity among crop species, where different crops occupy different ecological niches, leading to more efficient resource use [90,91]. This suggests that the benefits of growing different crops in a rotation are maximized when the crops occupy different ecological niches and their growth does not overlap in time or resource use [92,93]. The crop that precedes the gain crop (the crop expected to benefit from the rotation) can leave a legacy of improved conditions, such as enhanced soil fertility or reduced pest pressure, which can positively impact the subsequent crop’s yield [91,94]. For instance, the inclusion of functionally diverse crops, such as legumes and crops with varying root depths, leads to more efficient nutrient and water uptake, reduced pest pressure, and increased soil organic matter, all of which contribute to improved crop yields [95]. The greatest production benefits are observed in rotations with two to three functional groups, suggesting an optimal balance between diversity and yield [89]. However, the response to crop rotation diversity varies among indicator crops, highlighting the importance of crop selection in designing effective rotations [96].

The benefits of CRD are particularly pronounced under low external nitrogen input conditions [97], suggesting that diversified rotations can enhance nutrient-mediated benefits, especially in maize. The combination of diversified rotations with optimal nitrogen inputs results in the greatest yield benefits, indicating a potential strategy for reducing reliance on external nitrogen fertilization [89].

7. Outlook and Future Directions

The future of agriculture lies in the adoption of practices that enhance sustainability and resilience. CRD practices are at the forefront of these efforts, offering a pathway to achieve a more robust and environmentally friendly agricultural system. As research continues to uncover the potential of these practices, it is likely that we will see a greater emphasis on their integration into farming systems worldwide, leading to a more sustainable and resilient food production landscape [89,98,99,100].

Although the benefits of CRD are clear, there are challenges in designing rotations which balance multiple sustainability objectives [98]. Economic pressures and market demands may encourage farmers to grow a limited number of high-value crops, which undermine the effectiveness of these strategies. Additionally, the optimal length and sequence of crop rotations may vary depending on local conditions and pest pressures, requiring adaptive management approaches. The design of effective crop rotations is complex and requires a deep understanding of local agricultural systems and environmental conditions. Policy interventions should focus on providing the necessary support and incentives for farmers to adopt these sustainable agricultural practices. Governments and agricultural organizations should provide incentives for farmers to adopt these practices, such as subsidies for crop diversification or financial support for transitioning to conservation tillage. Education and extension services are also crucial to inform farmers about the long-term benefits of CRD for soil health, yield stability, and environmental sustainability.

In the context of climate change, diversification offers several strategies to enhance resilience. One approach is incorporating climate-resilient crop varieties within the cropping system. Plant breeding programs aim to develop crop varieties with traits such as drought, heat, and pest resistance or early maturity [101]. By introducing these varieties alongside traditionally grown ones, farmers may spread risks and maximize their chances of a successful harvest despite challenging climatic conditions. In China, by leveraging spatially detailed solutions tailored to local conditions, crop switching presents a viable strategy for improving farmer incomes, maintaining national production, and enhancing environmental sustainability [102]. For instance, the Northeast Plain could benefit from a shift from maize to soybean and rice, while the Yangtze River Plain might see co-benefits from reducing rapeseed and rice in favor of wheat and maize [102].

Studies also need to explore the synergistic effects of crop diversity and conservation tillage practices, particularly in the context of increasing weather unpredictability, and to investigate the mechanisms by which crop rotation diversity affects weed dynamics and how these practices can be integrated with other weed management strategies to reduce reliance on herbicides. The complexity of allelopathic interactions, the diversity of allelochemicals, and the difficulty in functional characterization of candidate genes pose significant obstacles. Future research should focus on (1) the functional characterization of identified genes and their role in allelopathic interactions, (2) the exploration of the regulatory networks that control the production and secretion of allelochemicals, (3) understanding the perception and signaling mechanisms of allelochemicals in target plants, and (4) the development of molecular tools for the manipulation of allelopathic traits in crops for weed management.

The dynamics of SOC from agricultural management practices under climate change suggest that SOC stocks may decline in future projections, with the decomposition of SOC outweighing the increase in carbon inputs from altered management practices. However, residue management plays a crucial role, with global cropland SOC stocks declining less when residue retention management systems are applied [103]. It is important to note that, while increasing soil carbon sequestration can mitigate CO₂ emissions, it may also lead to increased nitrous oxide (N₂O) emissions, which could offset the benefits of carbon sequestration. Residue management, conservation tillage, and soil restoration practices can enhance carbon sequestration in soils, potentially mitigating the greenhouse effect by CO₂-enrichment [64].

In conclusion, the impending challenges of global food production and the increasing need for sustainable agricultural systems call for an urgent shift towards CRD practices [17,104], aiming to optimize these practices for different environmental and management contexts, understanding their role in integrated pest and weed management, and assessing their resilience to climate change. Together, these efforts can contribute to a more productive and sustainable agricultural system.