A review of research progress on continuous cropping obstacles

Abstract

● Continuous cropping obstacles (CCOs) cause, on average, 22% reduction in crop production, seriously threatening sustainable agricultural development.

● Changes in the soil ecological environment are an essential and easily overlooked cause of CCOs.

● Studying CCOs from the perspective of the soil microbial food web may provide new approaches for explaining the formation mechanism of CCOs and controlling soilborne pathogens.

● Not all continuous cropping systems have CCOs, and some systems may enrich beneficial microorganisms to form healthy and disease-suppressive soil.

Due to the increasing global population and limited land resources, continuous cropping has become common. However, after a few years of continuous cropping, obstacles often arise that cause soil degeneration, decreased crop yield and quality, and increased disease incidence, resulting in significant economic losses. It is essential to understand the causes and mitigation mechanisms of continuous cropping obstacles (CCOs) and then develop appropriate methods to overcome them. This review systematically summarizes the causes and mitigation measures of soil degradation in continuous cropping through a meta-analysis. It was concluded that not all continuous cropping systems are prone to CCOs. Therefore, it is necessary to grasp the principles governing the occurrence of diseases caused by soilborne pathogens in different cropping systems, consider plant–soil-organisms interactions as a system, scientifically regulate the physical and chemical properties of soils from a systems perspective, and then regulate the structure of microbial food webs in the soil to achieve a reduction in diseases caused by soilborne pathogens and increase crop yield ultimately. This review provides reference data and guidance for addressing this fundamental problem.

Graphical abstract

Keywords

Continuous cropping obstacles / rhizosphere regulation / soil microecological environment

Highlight

	● Continuous cropping obstacles (CCOs) cause, on average, 22% reduction in crop production, seriously threatening sustainable agricultural development.
	● Changes in the soil ecological environment are an essential and easily overlooked cause of CCOs.
	● Studying CCOs from the perspective of the soil microbial food web may provide new approaches for explaining the formation mechanism of CCOs and controlling soilborne pathogens.
	● Not all continuous cropping systems have CCOs, and some systems may enrich beneficial microorganisms to form healthy and disease-suppressive soil.

1 Introduction

Continuous cropping obstacles (CCOs) refer to the phenomenon that the same crop or its related species are continuously planted on the same plot, and even under normal management conditions, the yield and quality of products are still reduced, and the diseases and insect pests become serious^[1–^3]. CCOs are caused by multiple biotic and abiotic factors, such as soil degradation, plant autotoxicity and changes in the soil biological community^[4]. Of these, rhizosphere microecological imbalance is the most crucial cause of CCOs^[5]. Soil microbial communities consist of various groups, such as bacteria, fungi, protozoa and nematodes. The relationships between these organisms constitute the soil microbial food web that is vital for soil health, nutrient cycling and agricultural productivity^[6,^7]. Currently, most studies on continuous cropping focus on single organisms, neglecting interactions between multiple organisms in soil food webs, which limits in-depth exploration of soil biological communities. Through a combination of meta-analysis and a summary of current research, we analyze the causes of CCOs and highlight the potential of soil food webs to evaluate them. Also, this review summarizes the incidence patterns of soilborne pathogens, and the disease they cause, in continuous cropping soils. It is important to note that not all continuous cropping systems are affected by to soilborne pathogens, and not all disease caused by soilborne pathogens are severe every year^[8–^12]. CCOs must be targeted based on a clear understanding of the principles governing their occurrence in different continuous cropping systems from the perspective of plant–soil-organisms interaction system. Our results provide a scientific basis for improving soil health and sustainable agricultural production.

2 Materials and methods

2.1 Data screening

The meta-analysis data set was compiled from peer-reviewed papers published before May 2023 and obtained from the Science Citation Index Expanded database of the Web of Science. The literature search terms used in this study were (TS = (“continuous cropping” OR “succession cropping” OR “monocropping”)) AND (TS = (microbiome OR microbiota OR bacteria OR bacterial OR fungi OR fungal OR nematode OR “physicochemical propert*” OR “physical and chemical propert*”)). To accurately screen for useful literature, we set a number of selection criteria: the research must consist of field or pot experiments from continuous cropping soils, excluding model simulations; it must involve continuous cropping age series, excluding soils for single-year cropping; at least one of the response variables (physical and chemical properties of soil or soil microbial community) had to be reported; only data obtained using high-throughput sequencing methods were collected, excluding data obtained using methods such as phospholipid fatty acid, denaturing gradient gel electrophoresis, or terminal restriction fragment-length polymorphism analyses; The microorganisms must be soil bacteria or fungi as a whole community, excluding studies that targeted specific groups of microorganisms such as mycorrhizal fungi or anaerobic bacteria; finally, definite replicate numbers were required (Fig. S1). Based on these criteria, we identified 112 publications, including a total of 1623 observations. Physical and chemical property indicators, such as soil pH, electrical conductivity, and total nitrogen, and soil microbial community indicators, such as the Chao1 and beta diversity indices, were recorded for each site described in these publications.

2.2 Data analyses

The natural logarithm of the response ratio (RR) was selected as the effect size to indicate the effects of continuous cropping on physical and chemical property indicators (e.g., pH, electrical conductivity and total nitrogen content) and soil microbial community indicators (e.g., Chao1, abundance-based coverage, and Shannon diversity and beta diversity indices), as^[13]:

(1)\mathrm{R}\mathrm{R}=\mathrm{l}\mathrm{n}\left(\frac{X_t}{X_c}\right)=\mathrm{l}\mathrm{n}{X}_t-\mathrm{l}\mathrm{n}{X}_c

where, X_t and X_c are the mean values of each indicator group, under continuous cropping treatment (t) and control (c) conditions, respectively. The variance (v) was calculated as:

(2)v=\frac{S_t^2}{n_t{X}_t^2}+\frac{S_c^2}{n_c{X}_c^2}

where, n_t and n_c are the sample sizes, S_t and S_c are the standard deviation of means under continuous cropping treatment (t) and control (c) conditions, respectively.

The percentage change (E) of the RR was calculated as:

(3)\mathrm{E}=\left({\mathrm{e}}^{\mathrm{R}\mathrm{R}}-1\right)\times 100\mathrm{\%}

Meta-analysis was conducted using the rma.mv function of the R package “metafor”^[14] to assess the overall effects of continuous cropping on physical and chemical properties and the soil microbial community. To account for the dependence of multiple observations in the same study, we included the study and site as random factors in the meta-analysis model. We considered the estimated parameter to be significant when the 95% CI did not overlap with zero^[15]. Linear fitting was performed for the relationship between the RR of yield/pH and continuous cropping years. All graphs were drawn using R packages “meta”^[16] and “ggplot2”^[17].

We collected soil microbial community structure and beta diversity data from two-dimensional ordination plots. Specifically, we extracted values from scatter plots in each two-dimensional ordination plot of treatment and control, thereby achieving a meta-analysis (based on one-dimensional data) of community data from two-dimensional ordination plots. The methods followed were as previously described in detail^[18]. The ordination plots included non-metric multidimensional scaling, principal component analysis, principal correspondence analysis and redundancy analysis. The symbols and colors used in the figures follow those of previous publications^[10,^19].

3 Current status of CCOs research

Given the threat of CCOs to global food security, research attention to these issues has gradually increased in recent years and has shown rapid progress. In a preliminary search of the Science Citation Index Expanded database, we found that the number of publications and citations related to continuous cropping has increased exponentially since 2000 (Fig.1). Such studies involve agronomy, environmental science, ecology and other major research fields (Fig.1). According to the global distribution of research related to continuous cropping, about 77% of the research has originated from China (Fig.1). Therefore, we used China as an example to conduct a follow-up analysis.

Continuous cropping has been applied to the cultivation of grain crops (rice and wheat), vegetable crops (tomato and cucumber), economic crops (tobacco and peanut) and medicinal crops (Panax ginseng and P. notoginseng) (Fig.2). Among all continuous cropping crops, economic, medicinal, food, vegetable, fruit and forage crops account for about 31%, 23%, 18%, 18%, 6% and 3%, respectively (Fig.2). CCOs have been reported in almost all provinces in China (Fig.2). Notably, the area of heavily affected continuously cropped land in China exceeds 10%, more than 20% of which is located in large-scale farming areas; crop losses reach 20% to 80%, and the associated economic losses will approach tens of billions of yuan^[20]. Thus, CCOs have become one of the most significant limiting factors restricting sustainable agricultural development in China.

4 Mechanisms underlying CCOs

CCOs result from the joint interaction of plants, soil and soil organisms. It is commonly believed that changes in soil physical and chemical properties, variations in soil ecological environment, and plant autotoxicity are the leading causes of CCOs^[1,^3]. These three mechanisms usually interact and jointly limit grain production capacity. Bibliometric analysis found that changes in soil physical and chemical properties, plant autotoxicity and variations in soil ecological environment accounted for 34%, 22% and 44% in CCO soil, respectively (Fig.2)^[5]. Therefore, biological factors may be the most crucial cause of CCOs.

4.1 Changes in soil physicochemical properties

Long-term continuous cropping and the excessive input of physiologically acidic fertilizers can easily lead to soil acidification. Excessive mineral fertilizer input reduces the average soil pH of Chinese fields by approximately 0.13–0.8^[21]. Our meta-analysis results preliminarily support this assessment. Research indicate that compared with non-continuous cropping, continuous cropping reduced soil pH in China by 8% on average (Fig.3) and that soil acidification will become increasingly severe as the duration of continuous cropping is extended (Fig.3). Soil acidification directly affects crop growth by affecting the content of metal ions in the soil, causing iron toxicity, aluminum toxicity and cadmium pollution^[22–^26]; inhibits the absorption of nutrients such as calcium, magnesium and phosphorus by crops^[27], and even indirectly limits increases in crop productivity by promoting the proliferation of acidophilic soilborne pathogens such as cyst nematodes, and the Fusarium wilt and bacterial wilt pathogens^[28,^29]. We also found that continuous cropping can both acidify and alkalize soil; the impact of continuous cropping on soil pH leads to one of these two extremes (Fig.3), which may be related to different fertilization management processes and the accumulation of specific root exudates during continuous cropping of plants. Studies have shown that the roots of plants that have been long-term irrigated with ammonia nitrogen fertilizer will secrete H⁺ to acidify the rhizosphere^[30]. In contrast, the roots of plants with long-term application of nitrate nitrogen fertilizer will secrete OH⁻ to alkalize the rhizosphere^[31]. Another manifestation of the changes in soil physicochemical properties is the stoichiometric imbalance between plants and soil. It was revealed that continuous cropping significantly increased total nitrogen in the soil by 24% and significantly increased available nitrogen, phosphorus and potassium by 32%, 64%, and 37%, respectively (Fig.3). However, this imbalanced nutrient enrichment does not necessarily benefit the soil and plants. According to stoichiometry theory, a balanced ratio of essential nutrients is crucial for optimal plant growth and soil health. Excess nutrient accumulation in soil can lead to an imbalance in the stoichiometric ratio of nutrients, compromising their availability and utilization by plants. This imbalance can result in nutrient runoff and leaching, degrading soil quality and negatively impacting long-term crop productivity^[32]. In addition, different plants have different nutrient requirements during the growth process. The selective absorption of soil nutrients, particularly trace elements, according to the physiologic needs of the plant during growth can also cause nutrient imbalance in soils, leading to various physiologic and functional disorders in crops that result in low yield and poor quality^[33]. Also, improper water and fertilizer management during continuous cropping increases the base ion concentration in the soil, also known as electrical conductivity^[34]. The analysis revealed that continuous cropping can increase electrical conductivity by 120% (Fig.3), which increases the risk for secondary soil salinization hazards that lead to crop yield reduction. Therefore, it is essential to consider the stoichiometric balance of nutrients in soil management practices to ensure sustainable agriculture and minimize the adverse effects of continuous cropping.

4.2 Plant autotoxicity

Autotoxicity, or self-toxicity, is a biological process where a species hinders the growth or reproduction of other members of its species by releasing certain chemicals into the environment^[35]. Autotoxic substances have been found in many crops (Tab.1). Notably, this effect harms crops directly while also facilitating the proliferation of pathogens, ultimately leading to poor crop growth, disease and death^[53]. Studies have shown that phenolic acids such as p-hydroxybenzoic acid, vanillic acid and coumaric acid in peanut root exudates accumulate in soil with the extension of continuous cropping duration and exhibit inhibitory effects on peanut growth^[54]. However, other studies have reached different conclusions, suggesting that phenolic acid compounds in peanut root exudates do not directly inhibit peanut growth but primarily disrupt the structure of soil microbial communities, leading to the proliferation of pathogenic bacteria in the soil and ultimately inhibiting peanut growth^[41]. In addition to peanuts, medicinal herbs and leafy vegetable crops are also prone to allelopathic autotoxicity. In medicinal plants, after 3 years of consecutive cultivation, the rhizosphere soil of Pseudostellaria heterophylla has accumulated organic acids such as tartaric acid and succinic acid, and P. notoginseng has phenolic compounds. These autotoxic substances severely damage the microbial community, resulting in significant yield reduction or even complete crop failure^[48,^49]. In vegetable crops, continuous cropping of eggplant for 3 years resulted in cinnamic acid and vanillin secretion in root exudates, which inhibited the growth of seedlings and promoted the proliferation of a Fusarium wilt pathogen^[55]. By comparison, continuous cropping of tomatoes for 7 years led to the accumulation of fatty acids in the rhizosphere soil, which inhibited seedling growth^[44], and continuous cropping of cowpeas for 8 years resulted in the accumulation of organic acids such as benzoic acid in the rhizosphere, which inhibited the growth of seedlings^[45]. The above studies have discovered different autotoxic substances related to continuous cropping and explored their harm to plants. The mechanism of plant allelopathy and autotoxicity in soil is much more complex than we imagined. Interspecific and intraspecific interactions among plants can be identified through chemical communication through released secondary substances, initiating corresponding growth and defense strategies, and producing corresponding allelopathic substances. Previous studies have revealed a density-dependent increase in DIMBOA concentration in wheat roots when co-cultivated with multiple weed species^[56,^57]. Kong et al.^[39] found that (–)-loliolide and jasmonic acid are present in root exudates from diverse species and can trigger wheat allelochemical DIMBOA production. DIMBOA is a specific allelopathic substance of wheat and other grass plants and are important for antibacterial, insect-resistant and weed suppression^[40]. Thus, the production of plant allelopathic substances involves a variety of complex signal exchanges within and between plant species. Starting from the ecological mechanism of allelopathy, exploring more allelopathic substances may be significant in alleviating plant autotoxicity.

4.3 Variations in the soil microbial food web

Continuous cropping can simplify the soil microbial food web and reduce its stability, reduce the diversity of nematodes and microorganisms in the soil, and increase the abundance of soilborne pathogens and phytophagous nematodes^[7]. A meta-analysis showed that continuous cropping significantly reduces bacterial and fungal diversity in rhizosphere soils and significantly alters microbial community structure but has only a minor effect on beta diversity (Fig.4). A reduction in soil biodiversity can reduce niche competition between soilborne pathogens and other microorganisms in the non-parasitic. The destruction of soil microbial community structure disturbs microecological functions, creating suitable conditions for the outbreak of soilborne pathogens. Notably, diseases caused by soilborne pathogens are the most direct, primary manifestation of CCOs, with more than 70% of the damage caused by CCOs resulting from soilborne pathogens^[58]. Data integration analysis showed that CCOs increased the plant disease index by an average of 395% (Fig.5). The most commonly reported soilborne pathogens caused by continuous cropping are soft rot, root rot, fusarium wilt, nematodes and ear rot diseases, which increase the plant disease index by an average of 35%, 30%, 22%, 20% and 15% (Fig.5).

The above studies enhance understanding of soil biological factors in continuous cropping. However, most current studies on biological factors of continuous cropping only focus on a single community of bacteria or fungi, and few studies focus on the interaction between nematodes, protozoa and multiple biological communities. According to data obtained from the Web of Science database, studies related to CCOs and biological communities showed that bacteria, fungi, nematodes and protozoa accounted for 50%, 46%, 3.7%, and 0.7%, respectively (Fig.4). There are 380 articles on single community research. By comparison, only five articles focus on the interaction of three or more communities (Fig.4). Studying the multitrophic interactions of soil microbial ecosystems from the perspective of soil food webs is significant to understanding of soil health. Soil degradation caused by continuous cropping will ultimately promote the abundance of pathogens and reduce the abundance of beneficial organisms by changing the soil microbial food web structure^[2]. Although the study of CCOs from the perspective of soil food webs has not received much attention at present, it is believed that with the maturity of sequencing technology and the development of multiomics analysis technology in the future, analyzing CCOs from the perspective of soil food webs will become a research hotspot.

5 Incidence patterns of soilborne pathogens in continuous cropping soils

There are three main incidence patterns of disease caused by soilborne pathogens in continuous cropping (Tab.2). Firstly, persistent severe, characterized by continuous serious plant disease during the entire continuous cropping process, resulting in severe crop yield reduction or even crop failure. For example, watermelon production will decrease by 25% after 21 consecutive years, and cucumber production will reduce by 50% after 20 consecutive years^[59,^60]. The main reason for this phenomenon is soil degradation and changes in the soil ecological environment caused by continuous cropping^[2]. Secondly, reduced in later stages, manifestation is that diseases caused by soilborne pathogens are serious in the early stage of continuous cropping, pathogen-suppressive soil is formed in the later stage of continuous cropping, and plant diseases are reduced. Some researchers have proposed that soil exhibits self-healing properties against soilborne pathogens during continuous cropping. In the late stage of continuous cropping, plants recruit beneficial microorganisms to facilitate their resistance to soilborne pathogens, thereby triggering soil-specific immunity and forming a disease-suppressing soil^[9]. For example, studies on soybean cyst nematodes have shown that the disease is severe within the first 5 years of continuous cropping but is gradually alleviated after that, accompanied by an enrichment of beneficial soil microorganisms, such as Pseudomonas; some studies that have focused on wheat take-all disease have demonstrated similar disease patterns after continuous cropping^[12,^75]. To verify this hypothesis further, we conducted a meta-analysis on the yield effects of crops under different continuous cropping years. The impact of continuous cropping on crop yield varies across studies. In most studies, it reduced crop yields. However, a few studies have found that continuous cropping can promote the formation of disease-suppressive soils, increasing crop yield in the later stages (Fig. S2). The yield-reduction effect of continuous cropping differs among crops. The yield of most crops will decrease with the increase of continuous cropping years. However, soybean yield does not change significantly with the rise of continuous cropping years. Some studies even found that continuous soybean cropping is conducive to forming pathogen-suppressive soil^[10]. Achyranthes bidentata is a crop that tolerates continuous cropping, and continuous cropping is beneficial for increasing its yield (Fig.5). The analysis revealed that the yield-reduction effect caused by continuous cropping decreased with cropping duration, although this effect was insignificant (P = 0.058) (Fig.6). We conclude that there may be a self-healing process in the soil in response to continuous cropping stress. Finally, continuous fluctuation, which is characterized by a cycle of alternating severe disease periods and milder disease periods during continuous cropping. The reason for this phenomenon may be the result of the coevolution of plants and pathogens. Jones and Dangle proposed the zigzag model to explain the co-evolution of plant immunity and pathogen infection in detail at the molecular level^[76].

6 Comprehensive mitigation measures for CCOs

The regulation of soil health can be achieved through various measures including physical, chemical and biological interventions to manage the rhizosphere ecosystem comprehensively. This process involves regulating the ecology of soil and crop growth processes and interactions among soil organisms to maintain soil health and provide adequate protection effectively^[77]. Soil organisms do not exist in isolation but form a complex network interacting through symbiosis, competition, predation and other mechanisms that collectively contribute to ecological regulation^[7]. Previous studies on CCOs have largely overlooked the role of biological regulation and the regulatory effect of the microbial food web on nutrient cycling and energy flow. There has been an excessive focus on fertility indicators and an overreliance on management practices that depend heavily on excessive irrigation, excessive fertilizer use and chemical inputs. This approach is taken at the expense of the environment and sustainability of soils and severely impacts the safety and quality of agricultural products. It also significantly hinders sustainable agricultural development and efficient resource utilization. Therefore, based on the multi-factor induction mechanism of CCOs, breakthroughs in the reduction of CCOs should be made in the following aspects in the future.

6.1 Scientific and accurate management of fertilizer

During continuous cropping, farmers often rely on excessive mineral fertilizer application as the primary method to improve soil fertility and increase crop yield while neglecting the use of organic fertilizers. This practice increases production costs and leads to a series of problems, including soil compaction, acidification and salinization, as well as groundwater pollution and excessive nitrate levels^[78]. In comparison, organic fertilizers provide a more balanced supply of nutrients and enhance soil water and nutrient retention capacity. Long-term application of organic fertilizers promotes the formation of soil aggregates, improves the physical and chemical properties of soils, mitigates issues caused by excessive mineral fertilizer use, and enhances disease suppression in soils^[79]. In addition, organic fertilizers can regulate the structure of the microbial food web. Increasing the application of organic fertilizers improves the rate of bacterial degradation and affects the activity and function of nematodes at lower trophic levels in the food web. From the perspective of the nematode community structure and function in the soil, appropriate increases in organic fertilizer application can promote nutrient cycling and energy flow within the soil microbial food web^[80]. Therefore, reducing the use of mineral fertilizers and partially substituting these with organic fertilizers are important measures for mitigating CCOs. Also, different crops have different nutrient requirements at different growth stages. It is necessary to scientifically tailor fertilizer applications based on soil properties, fertilizer characteristics and crop traits. This is essential to improve overall soil nutrient utilization efficiency and alleviate problems associated with improper fertilizer management during continuous cropping.

6.2 Optimizing cropping patterns

Optimizing the cropping patterns and breaking the cycle of monoculture is the most direct approach to overcoming CCOs. A positive correlation between biodiversity and ecosystem functioning has long been established, and evidence suggests that plant community diversity influences soil microbial diversity and functions, thereby promoting functions necessary for sustainable agriculture^[81]. Crop rotation and intercropping are commonly applied strategies for optimizing cropping patterns. Proper crop rotation can effectively regulate imbalances in soil microbial communities caused by continuous cropping, restore soil ecosystem services, and mitigate biological obstacles associated with continuous cropping. For example, banana-pineapple rotation significantly reduces the incidence of banana soilborne wilt and pineapple residues can induce an increased abundance of antagonistic fungi such as Trichoderma and Fusarium, promoting the formation of suppressive soils^[82]. Rotation with leguminous crops such as faba beans can improve the physicochemical properties of soils, enhance enzyme activity and increase crop yield^[83]. Intercropping can enhance the plant root system, nutrient availability and nutrient uptake efficiency promoting microbial activity. In a maize-peanut intercropping system, peanut rhizobia contributes to nitrogen fixation, improving the available nitrogen nutrition for maize plants; the maize, in turn, releases exudates that increase available iron that benefits peanuts^[84,^85]. Intercropping cassava and leguminous crops increases nutrient use efficiency and soil microbial diversity and significantly reduces the incidence of cassava root rot^[86]. Studies on peanut-cassava intercropping have shown that cyanide produced by cassava can induce ethylene signaling in intercropped peanuts, reshaping the rhizosphere microbial community, which in turn accelerates organic nitrogen and phosphorus mineralization, thereby improving nitrogen and phosphorus nutrient utilization and peanut yield^[87]. Thus, optimizing cropping patterns is a sustainable and practical approach to addressing the challenges of continuous cropping.

6.3 Conservation tillage

Conservation tillage refers to agricultural practices aimed at minimizing destructive mechanical operations while ensuring the sustainable use of agricultural, water, and soil resources^[88]. Techniques such as reduced tillage and no-till farming are considered forms of conservation tillage. Applying traditional tillage methods during continuous cropping involves frequent soil disturbance that can lead to soil compaction, nutrient and water loss, soil aggregate disruption, and reductions in organic matter content. Conservation tillage reduces soil disturbance by minimizing the number of large-scale mechanical field operations, thereby mitigating structural damage and moisture evaporation from the surface. This improves soil aggregates and organic matter content, reducing production costs and enhancing crop yields. A meta-analysis on north-eastern China indicates that conservation tillage can increase yields by about 0.8% compared to standard ridging and about 13.1% compared to deep tillage while also increasing organic carbon content by 17.4% to 43.9%^[89]. Conservation tillage can also change the soil microbial food web structure and promote soil health by increasing soil nematode abundance and maturity index, soil microbial biomass and diversity^[90]. Increasing attention has recently been focused on implementing appropriate conservation tillage practices.

6.4 Biological control

The primary mechanism of crop yield reduction caused by CCOs is soilborne pathogens caused by an imbalance of the soil microbial food web; therefore, improving the health level of continuous cropping soil from the perspective of regulating soil microbial food web stability would help achieve sustainable crop yield increases. Disease-suppressive soils harbor many beneficial microorganisms in the natural environment. In the form of biological control for continuous cropping soil, beneficial microorganisms in various complex environments, including disease-suppressing soil, are screened in a targeted manner, cultured in a laboratory, and then returned to disease-susceptible soils in the form of bacterial agents or bio-organic fertilizers; this helps produce a healthy and stable microbial food web structure^[91]. Beneficial microorganisms in the soil effectively promote organic phosphorus mineralization, enhance the bioavailability of soil nutrients and inhibit soilborne pathogens through mechanisms such as inducing plant resistance, antagonizing pathogens and competing for ecological niches^[92–^94]. Commonly applied exogenous microbial agents include species of Bacillus, Pseudomonas, Penicillium, Streptomyces, Trichoderma and arbuscular mycorrhizal fungi. Bacillus has been widely applied in controlling soilborne pathogens such as wilting pathogen, soft rot bacteria and root-knot nematodes. For example, Bacillus amyloliquefaciens has been shown to synergistically suppress banana wilt disease in conjunction with Pseudomonas^[95–^97], and arbuscular mycorrhizal fungi can activate soil phosphorus and promote its availability^[98]. These microorganisms can also induce plant resistance, indirectly helping plants to suppress diseases^[99].

Another biological control method is to identify functional substances of plant origin or microbial origin in nature and apply them in the field. In nature, there are host and non-host plant of various soilborne pathogens, and for some host crops there are resistant and susceptible cultivars. Therefore, developing multiple experimental methods to explore functional substances in the root exudates of non-host plants and resistant cultivars will benefit the eco-friendly and efficient control of soilborne pathogens. Root-knot nematode is a common soilborne organism found in continuous vegetable cultivation in China. A comparison of the differences in root exudates between tomato, a root-knot nematode host plant, and Garland chrysanthemum and Ricinus communis, which are non-host plants, led to the identification of lauric acid as a root exudate from G. chrysanthemum and palmitic acid and linoleic acid as root exudates from R. communis. These three substances exhibited inhibitory effects on the hatching and mortality of second-stage juveniles of the Meloidogyne incognita. They interfered with nematode migratory behavior by regulating the expression of the Mi-flp-18 gene^[100]. In another study, functional substances for controlling the southern root-knot nematode were identified and screened from fermented chicken manure and waste liquid from cassava alcohol production, leading to the discovery that methyl palmitate, methyl stearate, and triethyl phosphate, which cause mortality in second-stage nematode juveniles, inhibited nematode egg hatching and repelled second-stage juveniles. Significantly, these functional substances did not impact the reproduction of beneficial soil nematodes such as the free-living Caenorhabditis elegans^[101,^102]. These studies provide necessary theoretical and technical foundations for developing environmentally friendly nematode control agents and functional green, intelligent fertilizers.

7 Conclusions

In recent years, soil CCOs have become an agricultural research hotspot worldwide, and significant progress has been made in researching this issue. CCOs are the outward manifestations of the comprehensive interactions among plants, soil, microorganisms and the environment. Continuous cropping can lead to the accumulation of phenolic acids, sustained soil acidification, increased soilborne pathogens, and reduced beneficial microorganisms, ultimately resulting in an imbalance of the entire soil microbial ecosystem and significant crop yield reduction. Pathogen-suppressive soil has stable physical and chemical properties and can enrich beneficial soil microorganisms to contribute to the resistance of plants to soilborne pathogens (Fig.7). Based on the rhizobiont theory^[103], nutrient absorption occurs across multiple interfaces (soil-organisms-plants). Therefore, addressing CCOs requires their mitigation among these interfaces.

Widely-established cultivation practices depend heavily on excessive irrigation, intense fertilizer application and chemical pesticide usage. This approach has been taken at the cost of the health and sustainability of the soil environment, with significant impacts on the safety and quality of agricultural products. Therefore, fertilizers and pesticides must be applied scientifically and rationally, for example, by partially replacing mineral fertilizers with organic fertilizers and chemical agents with biocontrol agents.

Soil organisms are also crucial for soil health and represent the biological foundation for soil immunity and disease suppression. Nematodes and other microorganisms in the soil are critical components of the soil community, and their interactions are essential for various ecosystem functions, such as the decomposition and mineralization of organic matter and geochemical elemental cycling^[104]. Therefore, more attention must be given to the role of biological indicators in assessing CCOs through measures such as proper fertilizer management, optimized cropping patterns and conservation tillage to regulate the structure of the soil microbial food web.

Finally, we emphasize that continuous cropping does not always worsen soil health; it can also improve soil conditions and form pathogen-suppressive soils. It is necessary to fully excavate the microbial resources in pathogen-suppressive soil during the late stage of continuous cropping, cultivate and enrich these beneficial microorganisms, and return them to non-suppressive soil to regulate the microecological community. This practice will allow us to achieve stable crop yields, improve productivity, and promote sustainable agricultural development.

References

[1] Chen Y, Du J, Li Y, Tang H, Yin Z, Yang L, Ding X. Evolutions and managements of soil microbial community structure drove by continuous cropping. Frontiers in Microbiology, 2022, 13: 839494

[2] Pervaiz Z H, Iqbal J, Zhang Q, Chen D, Wei H, Saleem M. Continuous cropping alters multiple biotic and abiotic indicators of soil health. Soil Systems, 2020, 4(4): 59

[3] Sparks D L. Advances in Agronomy. Elsevier, 2023

[4] Zeeshan Ul Haq M, Yu J, Yao G, Yang H, Iqbal H A, Tahir H, Cui H, Liu Y, Wu Y. A systematic review on the continuous cropping obstacles and control strategies in medicinal plants. International Journal of Molecular Sciences, 2023, 24(15): 12470

[5] Xia M, Zhong W, Ouyang L S, Zhang Z, Zhang Z. Research status of continuous cropping obstacles in China from 1989 to 2018: based on bibliometric analysis and knowledge mapping of CNKI. Journal of Agriculture, 2021, 11(3): 46−54 (in Chinese)

[6] Neemisha. Role of soil organisms in maintaining soil health, ecosystem functioning, and sustaining agricultural production. In: Giri B, Varma A, eds. Soil Health. Springer, 2020, 313–335

[7] Milkereit J, Geisseler D, Lazicki P, Settles M L, Durbin-Johnson B P, Hodson A. Interactions between nitrogen availability, bacterial communities, and nematode indicators of soil food web function in response to organic amendments. Applied Soil Ecology, 2021, 157: 103767

[8] Wang J, Wu L, Tantai H, Khan M U, Letuma P, Wu H, Zhang S, Chen T, Lin S, Lin W. Properties of bacterial community in the rhizosphere soils of Achyranthes bidentata tolerant to consecutive monoculture. Plant Growth Regulation, 2019, 89(2): 167–178

[9] Raaijmakers J M, Mazzola M. Soil immune responses. Science, 2016, 352(6292): 1392–1393

[10] Liu Z, Liu J, Yu Z, Li Y, Hu X, Gu H, Li L, Jin J, Liu X, Wang G. Archaeal communities perform an important role in maintaining microbial stability under long term continuous cropping systems. Science of the Total Environment, 2022, 838: 156413

[11] Yin C, Casa Vargas J M, Schlatter D C, Hagerty C H, Hulbert S H, Paulitz T C. Rhizosphere community selection reveals bacteria associated with reduced root disease. Microbiome, 2021, 9(1): 86

[12] Hamid M I, Hussain M, Wu Y, Zhang X, Xiang M, Liu X. Successive soybean-monoculture cropping assembles rhizosphere microbial communities for the soil suppression of soybean cyst nematode. FEMS Microbiology Ecology, 2017, 93(1): fiw222

[13] Hedges L V, Gurevitch J, Curtis P S. The meta-analysis of response ratios in experimental ecology. Ecology, 1999, 80(4): 1150–1156

[14] Viechtbauer W. Conducting meta-analyses in R with the metafor package. Journal of Statistical Software, 2010, 36(3): 1–43

[15] Zhang Z, Liu Y, Yuan L, Ewald W, van Kleunen M. Effect of allelopathy on plant performance: a meta-analysis. Ecology Letters, 2021, 24(2): 348–362

[16] Balduzzi S, Rücker G, Schwarzer G. How to perform a meta-analysis with R: a practical tutorial. Evidence-Based Mental Health, 2019, 22(4): 153–160

[17] Villanueva R A M, Chen Z J. ggplot2—Elegant graphics for data analysis (2nd edition). Measurement: Interdisciplinary Research and Perspectives, 2019, 17(3): 160–167

[18] Zhou Z, Wang C, Luo Y. Meta-analysis of the impacts of global change factors on soil microbial diversity and functionality. Nature Communications, 2020, 11(1): 3072

[19] Perkel J M. The software that powers scientific illustration. Nature, 2020, 582(7810): 137–138

[20] TLi T, Yang L. Overcoming continuous cropping obstacles—The difficult problem. Scientia Agricultura Sinica, 2016, 49(05): 916−918 (in Chinese)

[21] Guo J H, Liu X J, Zhang Y, Shen J L, Han W X, Zhang W F, Christie P, Goulding K W T, Vitousek P M, Zhang F S. Significant acidification in major chinese croplands. Science, 2010, 327(5968): 1008–1010

[22] Zhu H, Chen C, Xu C, Zhu Q, Huang D. Effects of soil acidification and liming on the phytoavailability of cadmium in paddy soils of central subtropical China. Environmental Pollution, 2016, 219: 99–106

[23] Kunhikrishnan A, Thangarajan R, Bolan N S, Xu Y, Mandal S, Gleeson D B, Seshadri B, Zaman M, Barton L, Tang C, Luo J, Dalal R, Ding W, Kirkham M B, Naidu R. Functional relationships of soil acidification, liming, and greenhouse gas flux. In: Sparks D L, ed. Advances in Agronomy. Elsevier, 2016, 139: 1–71

[24] Shi R Y, Ni N, Nkoh J N, Dong Y, Zhao W R, Pan X Y, Li J Y, Xu R K, Qian W. Biochar retards Al toxicity to maize (Zea mays L.) during soil acidification: the effects and mechanisms. Science of the Total Environment, 2020, 719: 137448

[25] Meng C, Tian D, Zeng H, Li Z, Yi C, Niu S. Global soil acidification impacts on belowground processes. Environmental Research Letters, 2019, 14(7): 074003

[26] Yadav D S, Jaiswal B, Gautam M, Agrawal M. Soil acidification and its impact on plants//plant responses to soil pollution. In: Singh P, Singh S K, Prasad S M, eds. Plant Responses to Soil Pollution. Springer, 2020, 1–26

[27] Han T, Cai A, Liu K, Huang J, Wang B, Li D, Qaswar M, Feng G, Zhang H. The links between potassium availability and soil exchangeable calcium, magnesium, and aluminum are mediated by lime in acidic soil. Journal of Soils and Sediments, 2019, 19(3): 1382–1392

[28] Tyagi S, Paudel R. Effect of different pH on the growth and sporulation of Fusarium oxysporum: the causal organism of wilt disease of tomato. In: International Congress on “Agriculture, Forestry, Horticulture, Aquaculture, Animal Sciences, Food Technology, Biodiversity and Climate Change Sustainable Approaches” (AFHAFBC-2014), New Delhi. International Journal of Basic and Applied Biology, 2014, 2(1): 103–106

[29] Hua C, Li C, Jiang Y, Huang M, Williamson V M, Wang C. Response of soybean cyst nematode (Heterodera glycines) and root-knot nematodes (Meloidogyne spp.) to gradients of pH and inorganic salts. Plant and Soil, 2020, 455(1–2): 305–318

[30] Dal Molin S J, Ernani P R, Gerber J M. Soil acidification and nitrogen release following application of nitrogen fertilizers. Communications in Soil Science and Plant Analysis, 2020, 51(20): 2551–2558

[31] Weng Z, Li G, Sale P, Tang C. Application of calcium nitrate with phosphorus promotes rhizosphere alkalization in acid subsoil. European Journal of Soil Science, 2022, 73(1): e13153

[32] Kulkarni S, Goswami A. Effect of Excess Fertilizers and Nutrients: A Review on Impact on Plants and Human Population. In: International Conference on Sustainable Computing in Science, Technology and Management, Jaipur. Elsevier Social Science Research Network, 2019, 2094–2099

[33] Kumar Bhatt M, Labanya R, Joshi H C. Influence of long-term chemical fertilizers and organic manures on soil fertility—A review. Universal Journal of Agricultural Research, 2019, 7(5): 177–188

[34] Xu Y, Li J, Yin X. Continuous cropping affects gross nitrogen transformations in subtropical acidic soils under greenhouse cultivation. Journal of Soil Science and Plant Nutrition, 2020, 20(4): 1596–1604

[35] Ma W, Tang S, Dengzeng Z, Zhang D, Zhang T, Ma X. Root exudates contribute to belowground ecosystem hotspots: a review. Frontiers in Microbiology, 2022, 13: 937940

[36] Bouhaouel I, Gfeller A, Fauconnier M L, Rezgui S, Amara H S, Jardin P. Allelopathic and autotoxicity effects of barley (Hordeum vulgare L. ssp. vulgare) root exudates. BioControl, 2015, 60(3): 425–436

[37] Serra N, Shanmuganathan R, Becker C. Allelopathy in rice: a story of momilactones, kin recognition, and weed management. Journal of Experimental Botany, 2021, 72(11): 4022–4037

[38] Wan N X, Yuan J C, He W, Long W J, Zhang Q, Zhou S M, Zheng S L. Autotoxicity of water extracts from different organs of potato. Journal of Zhejiang University (Agriculture and Life Sciences), 2016, 42(4): 411–418

[39] Kong C H, Zhang S Z, Li Y H, Xia Z C, Yang X F, Meiners S J, Wang P. Plant neighbor detection and allelochemical response are driven by root-secreted signaling chemicals. Nature Communications, 2018, 9(1): 3867

[40] Wang N, Kong C, Wang P, Meiners S J. Root exudate signals in plant-plant interactions. Plant, Cell & Environment, 2021, 44(4): 1044–1058

[41] Li X, Ding C, Hua K, Zhang T, Zhang Y, Zhao L, Yang Y, Liu J, Wang X. Soil sickness of peanuts is attributable to modifications in soil microbes induced by peanut root exudates rather than to direct allelopathy. Soil Biology & Biochemistry, 2014, 78: 149–159

[42] Huang Y Q, Han X R, Yang J F, Liang C H, Zhan X M. Autotoxicity of peanut and identification of phytotoxic substances in rhizosphere soil. Allelopathy Journal, 2013, 31(2): 297–308

[43] Ren X, He X, Zhang Z, Yan Z, Jin H, Li X, Qin B. Isolation, identification, and autotoxicity effect of allelochemicals from rhizosphere soils of flue-cured tobacco. Journal of Agricultural and Food Chemistry, 2015, 63(41): 8975–8980

[44] Cheng F, Ali M, Liu C, Deng R, Cheng Z. Garlic allelochemical diallyl disulfide alleviates autotoxicity in the root exudates caused by long-term continuous cropping of tomato. Journal of Agricultural and Food Chemistry, 2020, 68(42): 11684–11693

[45] Huang X, Bie Z, Huang Y. Identification of autotoxins in rhizosphere soils under the continuous cropping of cowpea. Allelopathy Journal, 2010, 25(2): 383–392

[46] Chen P, Wang Y, Liu Q, Zhang Y, Li X, Li H, Li W. Phase changes of continuous cropping obstacles in strawberry (Fragaria × ananassa Duch.) production. Applied Soil Ecology, 2020, 155: 103626

[47] Zhang Y, Xie Z, Wang F, Cheng Z, Liu Y, Li Z, Wang G, Zhang Z. Genome-wide identification and characteristics analysis of melon (Cucumis melo L.) MYB transcription factors and their responses to autotoxicity and saline-alkali stress. Tropical Plant Biology, 2022, 15(1): 93–109

[48] Wu H, Wu L, Zhu Q, Wang J, Qin X, Xu J, Kong L, Chen J, Lin S, Umar Khan M, Amjad H, Lin W. The role of organic acids on microbial deterioration in the Radix pseudostellariae rhizosphere under continuous monoculture regimes. Scientific Reports, 2017, 7(1): 3497

[49] Bao L, Liu Y, Ding Y, Shang J, Wei Y, Tan Y, Zi F. Interactions between phenolic acids and microorganisms in rhizospheric soil from continuous cropping of Panax notoginseng. Frontiers in Microbiology, 2022, 13: 791603

[50] Wang R, Liu J, Jiang W, Ji P, Li Y. Metabolomics and Microbiomics Reveal Impacts of Rhizosphere Metabolites on Alfalfa Continuous Cropping. Frontiers in Microbiology, 2022, 13: 833968

[51] Zhang X Y, Shi S L, Li X L, Li C N, Zhang C M, Yun A, Kang W J, Yin G L. Effects of autotoxicity on alfalfa (Medicago sativa): seed germination, oxidative damage and lipid peroxidation of seedlings. Agronomy, 2021, 11(6): 1027

[52] Golzardi F, Aghamollaei N. Seed treatment to overcome autotoxicity of forage Rape. Environmental and Agricultural Sciences, 2017, 2: 17–24

[53] Yuan Y, Zuo J, Zhang H, Zu M, Liu S. The Chinese medicinal plants rhizosphere: metabolites, microorganisms, and interaction. Rhizosphere, 2022, 22: 100540

[54] Li P, Wang X, Li Y, Wang H, Liang F, Dai C. The contents of phenolic acids in continuous cropping peanut and their allelopathy. Acta Ecologica Sinica, 2010, 30(8): 2128−2134 (in Chinese)

[55] Chen S, Zhou B, Lin S, Li X, Ye X. Accumulation of cinnamic acid and vanillin in eggplant root exudates and the relationship with continuous cropping obstacle. African Journal of Biotechnology, 2011, 10(14): 2659–2665

[56] Zhang S, Li Y, Kong C, Xu X. Interference of allelopathic wheat with different weeds. Pest Management Science, 2016, 72(1): 172–178

[57] Li Y, Xia Z, Kong C. Allelobiosis in the interference of allelopathic wheat with weeds. Pest Management Science, 2016, 72(11): 2146–2153

[58] Feng Y, Zhang H, Song X, Ge T, Zhu J, Zhou C, Cobb K, Yan X, Ruan R, Cheng P. Microalgae as a potential conditioner for continuous cropping obstacles for taro (Colocasia esculenta L. Schott) production. Journal of Cleaner Production, 2022, 369: 133356

[59] Gu X, Yang N, Zhao Y, Liu W, Li T. Long-term watermelon continuous cropping leads to drastic shifts in soil bacterial and fungal community composition across gravel mulch fields. BMC Microbiology, 2022, 22(1): 189

[60] Wang F, Wang X, Song N. Biochar and vermicompost improve the soil properties and the yield and quality of cucumber (Cucumis sativus L.) grown in plastic shed soil continuously cropped for different years. Agriculture, Ecosystems & Environment, 2021, 315: 107425

[61] Xiong W, Zhao Q, Zhao J, Xun W, Li R, Zhang R, Wu H, Shen Q. Different continuous cropping spans significantly affect microbial community membership and structure in a vanilla-grown soil as revealed by deep pyrosequencing. Microbial Ecology, 2015, 70(1): 209–218

[62] Zhao Y, Fu W, Hu C, Chen G, Xiao Z, Chen Y, Wang Z, Cheng H. Variation of rhizosphere microbial community in continuous mono-maize seed production. Scientific Reports, 2021, 11(1): 1544

[63] Pang Z, Dong F, Liu Q, Lin W, Hu C, Yuan Z. Soil metagenomics reveals effects of continuous sugarcane cropping on the structure and functional pathway of rhizospheric microbial community. Frontiers in Microbiology, 2021, 12: 627569

[64] Liu N, Shao C, Sun H, Liu Z, Guan Y, Wu L, Zhang L, Pan X, Zhang Z, Zhang Y, Zhang B. Arbuscular mycorrhizal fungi biofertilizer improves American ginseng (Panax quinquefolius L.) growth under the continuous cropping regime. Geoderma, 2020, 363: 114155

[65] Dong L, Xu J, Feng G, Li X, Chen S. Soil bacterial and fungal community dynamics in relation to Panax notoginseng death rate in a continuous cropping system. Scientific Reports, 2016, 6(1): 31802

[66] Xia F, Wang L, Chen J, Fu M, Wang G, Yan Y, Cui L. Variations of microbial community in Aconitum carmichaeli Debx. rhizosphere soilin a short-term continuous cropping system. Journal of Microbiology, 2021, 59(5): 481–490

[67] Wei W, Xu Y, Li S, Zhu L, Song J. Developing suppressive soil for root diseases of soybean with continuous long-term cropping of soybean in black soil of Northeast China. Acta Agriculturæ Scandinavica. Section B: Soil and Plant Science, 2015, 65(3): 279–285

[68] Allende-Molar R. Role of 2,4-Diacetylphloroglucinol Producing Pseudomonas fluorescens in the Suppression of Take-all and Pythium Root Rot of Wheat. Dissertation for the Doctoral Degree. Pullman: Washington State University, 2006

[69] Kwak Y S, Weller D M. Take-all of wheat and natural disease suppression: a review. Plant Pathology Journal, 2013, 29(2): 125–135

[70] Chng S, Cromey M G, Dodd S L, Stewart A, Butler R C, Jaspers M V. Take-all decline in New Zealand wheat soils and the microorganisms associated with the potential mechanisms of disease suppression. Plant and Soil, 2015, 397(1–2): 239–259

[71] Pan Y, Ji X, Zhou F, Li X, Zhang X, Peng Q, Zhang J. Long Term monocropping effects tobacco yield by regulating rhizosphere allelochemicals and microbial community. Journal of Biobased Materials and Bioenergy, 2023, 17(1): 65–78

[72] Schillinger W F, Paulitz T C. Natural suppression of Rhizoctonia bare patch in a long-term no-till cropping systems experiment. Plant Disease, 2014, 98(3): 389–394

[73] Shen Z, Penton C R, Lv N, Xue C, Ruan Y, Li R, Shen Q. Banana Fusarium wilt disease incidence is influenced by shifts of soil microbial communities under different monoculture spans. Microbial Ecology, 2018, 75(3): 739–750

[74] Wei Z, Yu D. Analysis of the succession of structure of the bacteria community in soil from long-term continuous cotton cropping in Xinjiang using high-throughput sequencing. Archives of Microbiology, 2018, 200(4): 653–662

[75] Weller D M, Raaijmakers J M, Gardener B B M, Thomashow L S. Microbial populations responsible for specific soil suppressiveness to plant pathogens. Annual Review of Phytopathology, 2002, 40(1): 309–348

[76] Jones J D G, Dangl J L. The plant immune system. Nature, 2006, 444(7117): 323–329

[77] Onet A, Dincă L C, Grenni P, Laslo V, Teusdea A C, Vasile D L, Enescu R E, Crisan V E. Biological indicators for evaluating soil quality improvement in a soil degraded by erosion processes. Journal of Soils and Sediments, 2019, 19(5): 2393–2404

[78] Geng W, Ma Y, Zhang Y, Zhu F. Research progress in soil health regulation technology for protected agriculture. Chinese Journal of Eco-Agriculture, 2022, 30(12): 1973−1984 (in Chinese)

[79] Van Bruggen A H C, Sharma K, Kaku E, Karfopoulos S, Zelenev V V, Blok W J. Soil health indicators and Fusarium wilt suppression in organically and conventionally managed greenhouse soils. Applied Soil Ecology, 2015, 86: 192–201

[80] Pan F, Han X, Li N, Yan J, Xu Y. Effect of organic amendment amount on soil nematode community structure and metabolic footprints in soybean phase of a soybean-maize rotation on Mollisols. Pedosphere, 2020, 30(4): 544–554

[81] Cappelli S L, Domeignoz-Horta L A, Loaiza V, Laine A L. Plant biodiversity promotes sustainable agriculture directly and via belowground effects. Trends in Plant Science, 2022, 27(7): 674–687

[82] Yuan X, Hong S, Xiong W, Raza W, Shen Z, Wang B, Li R, Ruan Y, Shen Q, Dini-Andreote F. Development of fungal-mediated soil suppressiveness against Fusarium wilt disease via plant residue manipulation. Microbiome, 2021, 9(1): 200

[83] Cao Y, Wu C, Wang L, Chen M, Zhao H, Bian X, Chen Y, Xia L. Rotation of broad bean improves the soil quality of facility green house. Legume Research, 2017, 40(4): 710–715

[84] Dai J, Qiu W, Wang N, Wang T, Nakanishi H, Zuo Y. From Leguminosae/Gramineae intercropping systems to see benefits of intercropping on iron nutrition. Frontiers in Plant Science, 2019, 10: 605

[85] Zuo Y, Zhang F, Li X, Cao Y. Studies on the improvement in iron nutrition of peanut by intercropping with maize on a calcareous soil. Plant and Soil, 2000, 220(1/2): 13–25

[86] de Medeiros E V, de Alcantara Notaro K, de Barros J A, Duda G P, de Cássia Henriques dos Santos Moraes M, de Queiroz Ambrósio M M, Negreiros A M P, Sales Júnior R. Soils from intercropped fields have a higher capacity to suppress black root rot in cassava, caused by Scytalidium lignicola. Journal of Phytopathology, 2019, 167(4): 209−217

[87] Chen Y, Bonkowski M, Shen Y, Griffiths B S, Jiang Y, Wang X, Sun B. Root ethylene mediates rhizosphere microbial community reconstruction when chemically detecting cyanide produced by neighbouring plants. Microbiome, 2020, 8(1): 4

[88] Reddy P P. Sustainable Intensification of Crop Production. Singapore: Springer, 2016

[89] He C, Niu J, Xu C, Han S, Bai W, Song Q, Dang Y P, Zhang H. Effect of conservation tillage on crop yield and soil organic carbon in Northeast China: a meta-analysis. Soil Use and Management, 2022, 38(2): 1146–1161

[90] Shen X, Wang L, Wang Y, Wang M, Yang D, Zhao J, Li G, Xuan Q, Wang L. Progress on the effects of conservation tillage on soil aggregates, microbes, and nematode communities. Journal of Agricultural Resources and Environment, 2020, 37(3): 361–370

[91] Sun X, Xu Z, Xie J, Hesselberg-Thomsen V, Tan T, Zheng D, Strube M L, Dragoš A, Shen Q, Zhang R, Kovács Á T. Bacillus velezensis stimulates resident rhizosphere Pseudomonas stutzeri for plant health through metabolic interactions. ISME Journal, 2022, 16(3): 774–787

[92] Hedden P, Sponsel V. A century of Gibberellin research. Journal of Plant Growth Regulation, 2015, 34(4): 740–760

[93] Khan N, Bano A, Curá J A. Role of beneficial microorganisms and salicylic acid in improving rainfed agriculture and future food safety. Microorganisms, 2020, 8(7): 1018

[94] Zamioudis C, Pieterse C M J. Modulation of host immunity by beneficial microbes. Molecular Plant-Microbe Interactions, 2012, 25(2): 139–150

[95] Tao C, Li R, Xiong W, Shen Z, Liu S, Wang B, Ruan Y, Geisen S, Shen Q, Kowalchuk G A. Bio-organic fertilizers stimulate indigenous soil Pseudomonas populations to enhance plant disease suppression. Microbiome, 2020, 8(1): 137

[96] Wei Z, Yang X, Yin S, Shen Q, Ran W, Xu Y. Efficacy of Bacillus-fortified organic fertiliser in controlling bacterial wilt of tomato in the field. Applied Soil Ecology, 2011, 48(2): 152–159

[97] Yuan S, Wang L, Wu K, Shi J, Wang M, Yang X, Shen Q, Shen B. Evaluation of Bacillus-fortified organic fertilizer for controlling tobacco bacterial wilt in greenhouse and field experiments. Applied Soil Ecology, 2014, 75: 86–94

[98] Bender S F, Conen F, Van Der Heijden M G A. Mycorrhizal effects on nutrient cycling, nutrient leaching and N₂O production in experimental grassland. Soil Biology & Biochemistry, 2015, 80: 283–292

[99] Wang H, Hao Z, Zhang X, Xie W, Chen B. Effect, mechanisms and application of arbuscular mycorrhizal fungi for biological control of Fusarium oxysporum-caused wilt: a review. Microbiology China, 2022, 49(7): 2819−2837 (in Chinese)

[100] Dong L, Li X, Huang C, Lu Q, Li B, Yao Y, Liu T, Zuo Y. Reduced Meloidogyne incognita infection of tomato in the presence of castor and the involvement of fatty acids. Scientia Horticulturae, 2018, 237: 169–175

[101] Lu Q, Liu T, Wang N, Dou Z, Wang K, Zuo Y. Nematicidal effect of methyl palmitate and methyl stearate against Meloidogyne incognita in bananas. Journal of Agricultural and Food Chemistry, 2020, 68(24): 6502–6510

[102] Lu Q, Wang K, Dou Z, Wang T, Zuo Y. Agro-industrial waste and a nematicidal substance therein (triethyl phosphate) are effective against Meloidogyne incognita of bananas. Industrial Crops and Products, 2023, 202: 117003

[103] Shen J, Bai Y, Wei Z, Chu C, Yuan L, Zhang L, Cui Z, Cong W, Zhang F. Rhizobiont: an interdisciplinary innovation and perspective for harmonizing resources, environment, and food security. Acta Pedologica Sinica, 2021, 58(4): 805−813 (in Chinese)

[104] Topalović O, Hussain M, Heuer H. Plants and associated doil microbiota cooperatively suppress plant-parasitic nematodes. Frontiers in Microbiology, 2020, 11: 313

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