1 Introduction

Citrus orchards are economically important agroecosystems, but their productivity and ecological stability depend fundamentally on soil quality and the management of orchard floor vegetation (Wang et al., 2022). In many orchard regions, especially where clean tillage or herbicide-maintained bare ground has long been used, understory management has accelerated soil organic matter mineralization, weakened enzyme activities, simplified microbial communities, increased compaction, and contributed to the broader degradation of physical, chemical, and biological fertility. This problem is especially significant because orchards can lose soil organic carbon more intensely than cereal systems under poor management, making the restoration of belowground fertility a central issue for sustainable fruit production. Against this background, grass cover has emerged as a nature-based orchard floor management strategy that can reduce erosion, improve infiltration, enhance biodiversity, and strengthen multiple ecosystem services while supporting longer-term soil carbon and nitrogen accumulation (Chen et al., 2024). Large meta-analyses show that, relative to clean tillage, grass cover increases soil organic carbon stocks by about 21.47% in orchards across China and markedly promotes soil organic carbon and total nitrogen accumulation in citrus orchards, with estimated gains of 19.98 Mg ha⁻¹ yr⁻¹ and 2.27 Mg ha⁻¹ yr⁻¹, respectively. These fertility gains extend beyond carbon storage: grass cover generally lowers bulk density, raises soil organic matter, increases total and available nitrogen and phosphorus, and improves nutrient conditions most clearly in topsoil layers, although available potassium responses are less consistent. Biological responses are similarly strong, with evidence that grass cover increases microbial biomass carbon, bacterial and fungal abundance, Shannon diversity, and multiple extracellular enzyme activities linked to carbon, nitrogen, and phosphorus cycling (Xiang et al., 2023). In citrus systems specifically, long-term living grass mulching has substantially increased available nutrients and enzyme activities, indicating that grass cover is not merely a weed-control measure but a practical tool for rebuilding nutrient cycling capacity and orchard ecosystem resilience.

The development of grass cover cultivation technology in orchards has progressed from simple substitution for bare-soil management to a more differentiated system involving species selection, establishment mode, mulching duration, residue return, and integration with fertilization and water management. Early agronomic understanding emphasized that orchard grassing could buffer microclimate, improve water infiltration, reduce erosion and evaporation, and promote soil nutrient retention through litter input and root turnover. More recent work has clarified that the effects of grass cover depend strongly on the type of cover vegetation. Leguminous covers often perform especially well in enhancing nitrogen availability, microbial biomass, and enzyme activity because higher biomass production and biological nitrogen fixation increase organic matter return and nutrient inputs (Wu et al., 2021). In citrus orchards, species screening studies found that Fabaceae species increased soil organic matter more clearly, while several covers, including white clover, common vetch, and mixed grass-legume systems, also provided strong weed suppression and broader improvements in microbial diversity and soil quality. Long-term studies further show that management duration matters: benefits are often modest in the first few years, can even include short-term nutrient competition, but become more pronounced after sustained cover establishment, especially after 8-10 years or under continuous multi-year grassing. Spatial arrangement also matters. Full coverage can maximize soil carbon and nitrogen accumulation, but in sloping citrus orchards strip mulching may better balance soil and water conservation with fruit yield, since full living mulching reduced yield under dry-season water competition in hilly south China. Research has also moved from measuring bulk fertility indices to resolving microbial mechanisms. Field experiments in citrus and other orchards show that cover crops can reshape bacterial and fungal communities, increase alpha diversity, strengthen co-occurrence network complexity, and alter functional groups associated with nutrient cycling, though these responses remain site-specific and depend on successful cover establishment, residue quality, and soil depth (Castellano‐Hinojosa et al., 2023). Residue decomposition studies further indicate that roots and shoots differ in decomposition dynamics and nutrient release, helping explain how returned biomass supports longer-term fertility maintenance and microbial stability. At the same time, several studies caution that grass cover does not uniformly improve every function: seeded covers may underperform spontaneous vegetation in some citrus systems, nitrogen limitation can constrain soil organic carbon gains, and yield responses are often neutral or context-dependent rather than universally positive.

Given this progress, the central scientific task is no longer to ask whether grass cover matters, but to clarify how, under which conditions, and through which biological pathways grass cover reshapes soil fertility and the citrus orchard ecosystem. Existing evidence already shows that understorey vegetation influences nutrient cycling, microbial activity, and ecosystem diversity and stability, and that integrating functional plants into orchard floors can counteract the adverse effects of intensive chemical management. However, the literature remains fragmented across regions, cover species, management durations, and response variables, with some studies emphasizing carbon sequestration, others enzyme activity, microbial networks, weed control, or tree nutrition, and with non-negligible tradeoffs involving water use or early-stage competition. Some work shows that spontaneous covers can improve physical and chemical fertility more effectively than seeded grass in citrus inter-rows, whereas other long-term orchard studies indicate that cover crop identity governs whether systems preferentially stimulate carbon-cycling or nitrogen-cycling functions. Cover intensity can also shift bacterial composition through changes in available nitrogen, underscoring that orchard ecosystem responses are regulated by management gradients rather than by a single binary treatment. Accordingly, this review aims to synthesize current evidence on the impacts of grass cover on soil fertility and the citrus orchard ecosystem by focusing on three linked dimensions: first, changes in soil physicochemical properties and carbon-nitrogen storage; second, responses of soil biological processes, including microbial communities, enzyme activities, and residue-mediated nutrient cycling; and third, ecosystem-level outcomes such as weed suppression, soil and water conservation, tree nutrition, yield stability, and management tradeoffs. On this basis, the review will compare different grass cover types, durations, and spatial configurations, identify the main factors controlling response heterogeneity, and provide a framework for selecting site-appropriate grass cover strategies that improve soil fertility while maintaining the ecological functioning and productive sustainability of citrus orchards.

2 Effects of Grass Cover Cultivation on Soil Physical Properties in Citrus Orchards

2.1 Improvement of soil structure and aggregate stability

Grass cover cultivation improves soil structure in citrus orchards primarily by increasing organic matter inputs, protecting the soil surface from raindrop impact, and promoting the formation of stable macroaggregates. In sloping citrus orchards, grass cover markedly increased the proportion of large aggregates and reduced erosion-associated carbon loss, indicating that aggregate stabilization is a central pathway through which covered orchards maintain structural integrity (Zheng et al., 2021). A broader orchard meta-analysis likewise showed that grass cover significantly increased soil organic matter across multiple depths, creating the material basis for better aggregation and structural development over time.

The structural benefits strengthen with sustained implementation and suitable cover type. In the Three-Gorges citrus region, terracing combined with grass cover significantly increased aggregate stability and saturated hydraulic conductivity while lowering bulk density, and it outperformed other conservation measures in improving surface-soil condition (Xu et al., 2010). More recent evidence from navel orange orchards further showed that five years of native grass management increased the proportion of macroaggregates and aggregate stability, while simultaneously enriching carbon and nitrogen within aggregates, suggesting that physical stabilization and nutrient sequestration develop together under long-term grass cover.

Figure 1 Mechanisms underlying grass cover-induced improvement of soil aggregate stability and structural resilience in citrus orchards

2.2 Regulation of soil water dynamics and environmental buffering capacity

Grass cover regulates soil water dynamics by intercepting rainfall energy, slowing overland flow, and enhancing infiltration, thereby increasing the orchard floor’s buffering capacity against intense precipitation. In a rainfall simulation study in citrus orchards of southern China, grass cover reduced runoff by 47.28%-82.12% and sediment by 97.84%-98.81% relative to bare land, showing that vegetation cover strongly moderates hydrological disturbance at the soil surface (Zheng et al., 2021). Under frequent heavy rainfall, all tested groundcovers reduced runoff and pollution losses to varying degrees, with Trifolium repens performing especially well, confirming that surface vegetation can buffer short-term storm impacts in red-soil citrus systems.

Long-term field observations indicate that this hydrological buffering is beneficial but not unlimited, because water conservation and water competition can coexist depending on coverage intensity and season. In a 15-year citrus study, living grass mulch improved topsoil physical properties and reduced runoff and erosion from the first year onward, but full mulching also lowered soil water content in the 0-40 cm layer during the late dry season compared with clean tillage, whereas strip mulching produced a milder trade-off. Evidence from orchard systems more broadly is consistent with this pattern: natural grass cover increased water movement and retention in Mediterranean orchards (Vignozzi et al., 2019), while in sloping citrus farmland, denser cover improved runoff interception and rainwater infiltration, with species differences tied to coverage persistence and biomass.

2.3 Reduction of soil compaction and optimization of the rhizosphere environment

Grass cover reduces soil compaction chiefly by lowering surface sealing and machinery-induced densification, while root growth and residue return improve pore continuity in the upper soil profile. Across Chinese orchards, meta-analysis showed a consistent decline in soil bulk density under grass cover across 0-20, 20-40, and 40-60 cm layers, indicating that compaction alleviation is not restricted to the immediate surface (Wang et al., 2024). In a citrus orchard study from eastern Spain, spontaneous inter-row vegetation decreased bulk density and increased surface hydraulic conductivity, suggesting that biologically mediated pore formation can restore physical fertility under traffic-stressed orchard floors.

Improvement of the rhizosphere environment appears to extend beyond simple loosening of soil and includes higher porosity, greater microbial activity, and more favorable nutrient turnover near roots. In pomelo orchard soils, legume cover crop and straw mulch reduced bulk density in the 0-20 cm layer and increased porosity by about 2.74%-3.01%, showing that conserved surface cover can create a more penetrable root zone. In citrus orchards, cover cropping also increased soil porosity in species-dependent ways, and grass-covered orchards across China showed higher microbial biomass, diversity, and enzyme activities, which indicates that physical improvement and rhizosphere biological activation commonly proceed together under grass cover management (Xiang et al., 2023). Overall, the evidence indicates that grass cover in citrus orchards generally improves soil structure, strengthens hydrological buffering, and relieves soil compaction, although the magnitude of benefit depends on cover type, duration, and whether full or strip coverage is used.

3 Regulation of Soil Fertility by Grass Cover Cultivation in Citrus Orchards

3.1 Promotion of soil organic matter accumulation and carbon cycling

Grass cover cultivation promotes soil organic matter accumulation in citrus orchards mainly by increasing continuous organic inputs from shoots, roots, and rhizodeposition while reducing the carbon losses associated with clean tillage. A recent meta-analysis focused specifically on citrus orchards showed that grass coverage significantly enhanced the accumulation rates of soil organic carbon and total nitrogen, and that microbial biomass carbon and dissolved organic carbon also increased after cover establishment (Chen et al., 2024). At a broader orchard scale, evidence from across China similarly indicated that grass coverage increased soil organic carbon stocks by 21.47% on average, with grass age emerging as one of the major determinants of the carbon sequestration response.

The effect on carbon cycling is not only quantitative but also strongly linked to residue quality, cover duration, and microbial mediation. In navel orange orchards, five years of native grass management significantly increased topsoil SOC by 118.3%-184.2% and total nitrogen by 73.3%-81.5%, while improving aggregate-associated carbon protection and enriching nutrient-cycling functional genes in soil aggregates. However, not all grass-cover systems produce equivalent carbon gains, because a citrus orchard study in eastern Spain found that seeded fescue improved biological conditions without increasing SOC, and identified insufficient nitrogen input as a likely constraint on carbon buildup under some cover regimes.

3.2 Regulation of soil nutrient availability and cycling processes

Grass cover regulates soil nutrient availability by altering nutrient inputs, retention, and transformation pathways, especially for nitrogen and phosphorus in surface soil. A national meta-analysis of orchard studies in China found that grass cover significantly increased topsoil total nitrogen and total phosphorus, while also increasing available nitrogen across all three sampled depths and available phosphorus within 0-40 cm, indicating a generally positive effect on nutrient supply capacity (Wang et al., 2024). In citrus orchards of southern China, grass cover also increased total organic nitrogen and enriched active organic nitrogen fractions in the 0-20 cm layer, while shifting total soluble nitrogen upward in the topsoil and downward in deeper layers, which suggests improved nutrient retention near the main rooting zone.

Nutrient-cycling responses depend on cover composition and duration, with legume-containing systems often showing stronger nitrogen-related effects. In a central China citrus orchard, greater grass biomass carbon and nitrogen were positively related to soil total carbon, nitrate, and dissolved organic carbon, while biologically fixed nitrogen was positively associated with soil total nitrogen and ammonium, indicating that both biomass return and N fixation help drive nutrient cycling. Consistent with this mechanism, Florida citrus orchards planted with combined legume and non-legume cover crops showed higher ammonium concentrations, greater nitrification and N mineralization rates, and lower N₂O emissions than non-legume-only systems, demonstrating that cover diversity can improve nutrient turnover while moderating gaseous nitrogen losses.

3.3 Effects on soil enzyme activities and nutrient transformation functions

Grass cover cultivation enhances soil enzyme activities in citrus orchards, and these changes reflect stronger microbial participation in carbon, nitrogen, and phosphorus transformation. A synthesis across Chinese orchards showed that grass cover increased the activities of invertase, urease, acid phosphatase, alkaline phosphatase, catalase, and cellulase, alongside clear increases in microbial biomass and the abundance of bacteria, fungi, and actinomycetes (Xiang et al., 2023). In subtropical citrus orchards, eight years of living grass mulching further increased β-glucosidase, cellobiohydrolase, N-acetylglucosaminidase, leucine aminopeptidase, and acid phosphatase activities, confirming that prolonged mulching strengthens C-, N-, and P-cycling functions in the 0-40 cm layer.

These enzymatic responses are closely tied to nutrient status and grass functional traits rather than representing a purely microbial abundance effect. In the same citrus mulching experiment, available nutrients explained nearly 70% of the variation in enzyme activities, and microbial C and P showed the strongest positive correlations with enzymatic responses, indicating that nutrient enrichment is a primary driver of functional activation. Evidence from long-term orchard cover systems also shows trait-specific functional differentiation: high C/N orchard grass preferentially stimulated C-cycle enzyme activity, whereas low C/N white clover more strongly promoted N-cycle enzyme activity and nitrogen-metabolism pathway genes, implying that grass species selection can be used to steer nutrient transformation functions in orchard soils (Wang et al., 2020). Overall, grass cover cultivation in citrus orchards tends to improve organic matter accumulation, strengthen nutrient retention and cycling, and enhance enzyme-mediated nutrient transformation, although the magnitude and direction of specific responses depend on cover species, nitrogen input, and management duration.

4 Effects of Grass Cover Cultivation on Soil Microbial Ecosystems in Citrus Orchards

4.1 Alteration of soil microbial community structure

Grass cover cultivation generally reshapes soil microbial community structure in citrus orchards by increasing microbial abundance, enriching diversity, and shifting the relative abundance of dominant bacterial and fungal groups. A synthesis across Chinese orchards showed that grass cover increased microbial biomass carbon, bacterial abundance, fungal abundance, actinobacterial abundance, and Shannon diversity, indicating that the microbial response is broad rather than confined to a single taxonomic group (Xiang et al., 2023). In a citrus orchard of southeast China, both Bermuda grass strip intercropping and full coverage significantly increased bacterial richness and fungal diversity relative to clear tillage, and full coverage supported more beneficial taxa with degrading and nutrient-cycling capabilities.

These compositional changes are also shaped by cover type, cover duration, and associated shifts in soil resources. After five years of different ground-cover treatments in central China citrus orchards, microbial community structure differed clearly between plots with and without legumes, and total carbon and grass biomass nitrogen were identified as major drivers of bacterial and fungal community variation. Similar duration-dependent responses were reported for leguminous mulching in subtropical orchards, where four- and eight-year Vicia villosa treatments increased bacterial and fungal alpha diversity and strengthened microbial network stability as mulching age increased (Wang et al., 2024).

4.2 Promotion of microbe-mediated nutrient cycling

Grass cover promotes microbe-mediated nutrient cycling in citrus orchards mainly by increasing substrate supply, nutrient availability, and the abundance of functionally active microbial groups. In subtropical citrus orchards, eight years of living grass mulching significantly increased available nitrogen and phosphorus, while also stimulating β-glucosidase, cellobiohydrolase, N-acetylglucosaminidase, leucine aminopeptidase, and acid phosphatase activities across the 0-40 cm profile, showing coordinated enhancement of carbon, nitrogen, and phosphorus cycling processes (Wang et al., 2022). A broader meta-analysis likewise found that grass cover increased orchard soil invertase, urease, acid phosphatase, alkaline phosphatase, catalase, and cellulase activities, supporting the conclusion that enzyme-mediated nutrient transformation is a consistent response across orchard systems.

The functional consequences extend to specific nutrient pools and specialized microbial guilds involved in nutrient mobilization. Long-term cover crops in orchard soils increased the abundance of phosphorus-solubilizing bacteria such as Streptomyces, Sphingomonas, Nocardioides, and Haliangium, while also enhancing alkaline phosphatase activity and increasing the bioavailability of several phosphorus fractions in surface soil. In citrus orchards, grass biomass carbon and nitrogen were positively associated with soil total carbon, nitrate, and dissolved organic carbon, whereas biologically fixed nitrogen was positively related to total nitrogen and ammonium, indicating that microbial nutrient cycling is strengthened through both residue return and legume-derived nitrogen inputs.

4.3 Regulation of rhizosphere interactions and plant health

Grass cover also regulates rhizosphere interactions in ways that can improve plant health by altering microbial recruitment, network stability, and the abundance of potentially beneficial taxa. In citrus orchards under long-term Bermuda grass management, microbial co-occurrence networks were more complex and robust than under clear tillage, and full coverage produced the highest network stability, suggesting a more resilient rhizosphere-associated microbial system. More generally, rhizosphere research shows that plants can shape microbiome assembly through root exudates and microbe-microbe competition, thereby recruiting beneficial bacteria and influencing nutrient acquisition and plant health outcomes (Pantigoso et al., 2022; Chepsergon and Moleleki, 2023).

Evidence from orchard systems further suggests that these rhizosphere effects can translate into improved crop performance, although the response depends on species composition and local conditions. In long-term bristlegrass-covered pear orchards, rhizosphere soils showed marked shifts in microbial composition and metabolites, enrichment of several plant growth-promoting rhizobacterial taxa, and strong associations between these changes and higher fruit yield and sugar-related quality traits (Shi et al., 2024). However, orchard studies are not fully uniform: one jujube study found that grass treatments changed microbial abundance more than overall diversity and that some nutrient indicators remained higher under clear tillage, indicating that grass cover effects on rhizosphere function and plant benefits are contingent on grass species, management duration, and site conditions. Overall, grass cover cultivation in citrus orchards tends to enhance microbial diversity, strengthen enzyme-mediated nutrient cycling, and stabilize rhizosphere microbial interactions, but the magnitude and direction of these benefits depend on cover species, nutrient inputs, and the duration and intensity of ground-cover management (Figure 2).

Figure 2 Mechanisms underlying grass cover-mediated regulation of rhizosphere microbial interactions and citrus plant health

5 Effects of Grass Cover Cultivation on Citrus Orchard Ecosystem Functions

5.1 Enhancement of biodiversity in orchard ecosystems

Grass cover cultivation generally enhances biodiversity in orchard ecosystems by adding plant structural complexity, food resources, and habitat continuity within the inter-row space. Orchard systems already have strong potential to sustain diverse food webs because their perennial, multi-strata structure can support beneficial organisms, and adding cover crops in alleys further increases habitat heterogeneity (Demestihas et al., 2017). In citrus-related orchard soils, grass cover also increases belowground biodiversity: across China, it raised microbial Shannon diversity by 9.4% and substantially increased the abundance of bacteria, fungi, and actinobacteria, indicating that biodiversity gains occur not only above ground but throughout the soil biotic network.

Evidence from orchard arthropod communities shows that these biodiversity effects often translate into greater abundance of beneficial taxa. In apple orchards, grass strips consistently supported higher densities of alternative prey and higher predator abundance than flower strips or controls, with the lowest aphid abundance observed where grass support was strongest. Similarly, in Mediterranean pear orchards, sown cover crops significantly increased the diversity and abundance of ground-dwelling arthropods, including spiders, carabids, staphylinids, and scelionids that are relevant to pest suppression (De Pedro et al., 2020).

5.2 Regulation of nutrient, water, and energy flows in orchards

Grass cover regulates nutrient and water flows mainly by intercepting rainfall, increasing infiltration, reducing runoff, and retaining sediment and nutrients within the orchard system. In sloping citrus orchards, groundcover generally reduced annual surface runoff, interflow, soil loss, and total nitrogen and phosphorus loss, with Lolium and Vicia performing better than Orychophragmus because their longer and denser surface coverage improved interception (Liu et al., 2024). More broadly across orchard systems, cover crops reduced runoff by 33%-60%, leaching by 33%-51%, soil loss by 30%-53%, and total C, N, and P losses by 30%-48%, 30%-49%, and 30%-38%, respectively, showing that vegetation cover can moderate multiple coupled material flows at once.

These hydrological effects are closely tied to energy dissipation at the soil surface and to changes in biogeochemical turnover. Ground-covering vegetation absorbs rainwater energy and protects the soil from aggregate disruption, crusting, and erosion, while also helping reduce machinery-related compaction (Vignozzi et al., 2019). In Florida citrus orchards, cover crops increased labile soil carbon and altered nitrogen-cycling gene abundances within one year, and legume plus non-legume mixtures increased ammonium while lowering N₂O fluxes relative to non-legume cover alone, indicating that grass cover can redirect both nutrient flow and gaseous loss pathways (Castellano‐Hinojosa et al., 2021).

5.3 Improvement of ecosystem services

By coupling higher biodiversity with better soil and water regulation, grass cover tends to improve multiple ecosystem services in orchards simultaneously. Orchard reviews indicate that groundcover increases humification, reduces denitrification and runoff, and enhances biotic interactions involved in pest control and pollination, linking one management practice to several provisioning and regulating services at once. At the broader grassland-farmland interface, semi-natural grasslands supported higher biodiversity as well as stronger pollination, soil fertility, carbon storage, and water regulation, and increased landscape grassland cover improved overall ecosystem-service multifunctionality (Tamburini et al., 2022).

The ecosystem-service gains are substantial but not uniform, and trade-offs remain important in citrus orchard management. Meta-analysis in apple orchards found that ground covers promoted natural enemies most strongly and tended to reduce pest insects while maintaining fruit quality, supporting their value for conservation biological control (Judt et al., 2023). However, long-term citrus experiments in South China showed that although full and strip living mulches reduced runoff and erosion from the first year, average fruit yield declined by 32.15% under strip mulching and 41.72% under full mulching, so ecosystem-service optimization depends on matching cover intensity to local water limitation and production goals. Overall, grass cover cultivation in citrus orchards tends to strengthen ecosystem functioning by increasing biodiversity, stabilizing water and nutrient retention, and improving multiple regulating services. The best outcomes appear under species and management combinations that maximize cover persistence and biological benefits while limiting competition with trees.

6 Effects of Grass Cover Cultivation on Citrus Growth, Yield, and Fruit Quality Formation

6.1 Effects on citrus tree growth and root development

Grass cover cultivation generally promotes citrus tree growth when the cover species are compatible with the orchard environment and competition for water is controlled. On sloping citrus land, both Lolium and Vicia significantly improved tree height, stem diameter, and crown width after two consecutive years, while foliar C, N, and P concentrations also increased under cover management. In young Tahiti acid lime orchards, ecological mowing combined with inter-row cover crops increased canopy volume, and ruzi grass performed better than signal grass because it imposed less competition on the trees (Martinelli et al., 2017).

The effects on root development appear to operate partly through improved nutrient metabolism rather than through growth stimulation alone. After two years of inter-row sowing, both rattail fescue and Vicia villosa significantly increased nitrate reductase, nitrite reductase, glutamine synthetase, NADH-GOGAT, and related nitrogen-metabolism gene expression in citrus roots at 0-20 cm, with rattail fescue showing the stronger response. However, short-term responses are not always expressed at the whole-tree level: in mature HLB-affected orchards in Florida, three years of legume and non-legume cover crop mixtures produced no significant short-term improvement in trunk cross-sectional area, although treatment-by-site and treatment-by-time interactions suggested context dependence rather than complete absence of effect (Brewer et al., 2025).

6.2 Effects on citrus yield formation

Grass cover can increase citrus yield, especially where it improves weed suppression, nutrient retention, and tree vigor without creating excessive competition. A recent review of citrus orchards reported that cover crops increased fruit yield by 7.6% to 64%, indicating that positive production responses are common under suitable management (Silwana et al., 2023). In young acid lime orchards, ruzi grass combined with ecological mowing produced 126% higher fruit yield than conventional mowing, and the addition of glyphosate within that integrated system further enhanced yield relative to non-glyphosate management.

Yield responses are nonetheless inconsistent across production contexts and often show a lag in perennial orchards. In two Florida citrus orchards, three years of cover cropping changed soil nutrient cycling and the microbiome but had no significant effect on fruit yield, and a separate two-year evaluation of five cover-crop management models in central China likewise detected no significant treatment effect on yield during the observation period (Tang et al., 2026). The strongest yield gains appear when grass cover is integrated with broader nutrient management: in hilly citrus orchards, the optimized system combining cover crops with organic and inorganic fertilization increased yield by 33.57% and economic returns by 45.51% compared with chemical fertilizer alone.

6.3 Effects on fruit quality and commercial value

Grass cover tends to improve fruit quality by enhancing nutrient availability, moderating rhizosphere processes, and supporting physiological traits linked to sugar and antioxidant accumulation. In protected citrus cultivation, both white clover and ryegrass significantly increased total soluble solids and vitamin C in mature fruits, while white clover more strongly increased iron availability and enriched siderophore-producing Pseudomonas associated with better fruit quality (Deng et al., 2026). More broadly, citrus-focused review evidence indicates that cover crops improved fruit quality by 2.3% to 12.4% in fruit weight and by 2.4% to 5.8% in soluble solids, supporting the view that quality benefits are recurrent rather than isolated.

Commercial value, however, depends on whether quality gains are large enough to offset costs and whether orchard conditions allow those gains to emerge within the evaluation period. Economic analysis in Florida showed that cover crop adoption increased first-year production cost by $107.3 per acre, so profitability under current low yield-quality conditions was not assured even though it became favorable at median ‘Valencia’ yield and solids levels (Chakravarty and Wade, 2023). This helps explain why some short-term citrus studies found no detectable effect of cover crops on fruit quality, particularly in mature or HLB-affected orchards where disease pressure, site variation, and the lagged response of perennial systems can mask benefits that become clearer over longer periods. Overall, grass cover cultivation generally benefits citrus growth, yield, and fruit quality formation, but the clearest gains occur with well-matched species, longer management duration, and systems that limit tree-cover competition while improving soil fertility.

7 Case Studies: Effects of Different Grass Cover Systems on Soil Fertility and Ecological Functions in Citrus Orchards

7.1 Case studies of artificial grass cover systems for soil improvement in citrus orchards

Artificially sown grass cover systems have shown clear capacity to improve soil fertility in citrus orchards, especially where the inter-row is otherwise kept bare. In subtropical citrus orchards, long-term Vicia villosa living mulching increased available nitrogen and phosphorus and strongly stimulated C-, N-, and P-cycling enzyme activities, with the effects becoming much stronger after eight years than after four years. A separate three-year case study of smooth vetch cover further showed that topsoil SOC, occluded particulate organic carbon, and lignin phenols increased under vetch cover, indicating that artificial legume cover can enhance both soil fertility and carbon stabilization pathways (Zhang et al., 2025).

Species choice within artificial systems also matters because different grasses alter water, nutrient, and tree responses in different ways. On sloping purple-soil citrus land, Lolium perenne and Vicia villosa were more effective than Orychophragmus violaceus in reducing runoff, soil erosion, and N and P loss, while also improving foliar nutrition and citrus growth. In sandy Florida orchards affected by huanglongbing, row-middle cover crop mixtures increased nitrate concentrations after seven consecutive seasons, and at one site they also increased soil organic matter, showing that even in low-retention soils, seeded systems can gradually strengthen nutrient availability.

7.2 Case studies of natural grass management for orchard ecosystem optimization

Natural grass management often performs well because it is locally adapted and can improve several ecological functions simultaneously with lower management intensity. In a five-year navel orange study on sloping land, intercropped native grasses significantly increased SOC and total nitrogen, improved aggregate stability, and enriched beneficial microbial diversity and nitrogen-cycling genes in soil aggregates. A global meta-analysis focused on citrus orchards also found that grass coverage increased SOC and STN accumulation rates, with stronger gains under longer grass age and full-orchard coverage, supporting the long-term value of persistent natural or near-natural cover.

Case studies comparing spontaneous vegetation with more intensively managed systems suggest that natural cover can sometimes outperform seeded grass in practical orchard conditions. In eastern Spain, spontaneous plants improved exchangeable potassium, increased surface hydraulic conductivity, and decreased bulk density, whereas fescue mainly improved biological fertility and failed to raise SOC under limited nitrogen supply (Visconti et al., 2022). In a Natal orange orchard in Brazil, spontaneous vegetation and brachiaria-based covers also outperformed full-area glyphosate management for organic matter and microbial biomass indicators, with soil organic matter under glyphosate falling 14.8% below spontaneous vegetation in 2019 (Shimizu et al., 2022).

7.3 Case studies integrating grass cover cultivation with sustainable citrus production

Integrated systems that combine grass cover with fertilizer optimization, mowing, or reduced tillage show the strongest evidence for balancing soil improvement with production goals. In hilly citrus orchards, the optimized management system integrating cover crops with organic-inorganic fertilization reduced carbon and water footprints while increasing yield by 33.57% and economic returns by 45.51% relative to chemical fertilizer alone (Ning et al., 2026). In high-density Tahiti acid lime orchards, no-tillage with Urochloa ruziziensis mulch increased leaf and soil potassium, improved soil moisture and penetration resistance, and raised fruit yield by 56% over conventional tillage during three harvests.

Integrated management also reveals the main trade-offs that determine whether grass cover improves whole-orchard sustainability. In South China, 15 years of living grass mulching improved topsoil physical properties and reduced runoff and erosion, but full and strip mulching reduced average fruit yield by 41.72% and 32.15%, respectively, indicating that soil conservation gains can be offset by dry-season competition if cover intensity is too high. More recent comparative trials in central China similarly showed that different cover-crop models rapidly changed soil water, available nutrients, and soil CO₂ flux, yet short-term effects on fruit quality and yield were not significant, reinforcing that integrated grass-cover systems need longer evaluation and site-specific adjustment to deliver stable multifunctional benefits. Overall, the case studies show that artificial, natural, and integrated grass-cover systems all improve citrus orchard soils, but their best use patterns differ. Artificial covers are effective for targeted nutrient and carbon gains, natural grass management is often strongest for low-input ecosystem optimization, and integrated systems are most promising for sustainable production when water competition and nutrient balance are carefully managed (Figure 3).

Figure 3 Mechanisms underlying the synergistic effects of grass cover cultivation combined with optimized fertilization, mowing, and reduced tillage on sustainable citrus orchard production

8 Constraints and Optimization Strategies for Grass Cover Cultivation Applications

8.1 Selection of grass species and optimization of management practices

A central constraint in citrus orchard grass cover systems is that different species deliver very different balances between weed suppression, soil improvement, and competition with trees. Comparative trials in citrus orchards showed that white clover, common vetch, rattail fescue, and white clover-ryegrass mixtures achieved high surface coverage and strong weed control, while Fabaceae tended to increase soil organic matter more clearly than cereal covers. Species effects also extend to tree responses: after two years on sloping citrus land, Lolium perenne and Vicia villosa improved foliar nutrition and vegetative growth more consistently than Orychophragmus violaceus, indicating that cover selection must prioritize compatibility with orchard conditions rather than biomass alone.

Management optimization therefore depends on matching functional traits to local constraints such as drought risk, slope, and fertility status. Broader orchard evidence shows that grass-cover outcomes vary with grass source, nitrogen-fixing ability, climate, soil pH and texture, orchard age, cover duration, and sowing mode, which argues against a single universal recommendation. Where water competition is a major risk, selected low-competition covers and mowing are preferable because mowing can reduce evapotranspiration and leave residue that still protects soil, while shallow-rooted and lower-biomass species are better suited to permanent orchard cover than highly competitive native vegetation (Capri et al., 2023).

8.2 Integrated regulation of grass cover systems with water and fertilizer management

Grass cover should be regulated together with water and fertilizer management because its ecological benefits can be offset if tree-cover competition is not buffered by adequate resource supply. In South China, long-term living mulching improved topsoil properties and reduced runoff and erosion, but full mulching also produced the lowest 0-40 cm soil water content in the dry season and reduced average fruit yield more than strip mulching, showing that water competition becomes a major limitation when cover intensity is too high. Similar trade-offs were observed in Florida citrus alleys, where cover crops increased deep winter soil moisture but reduced topsoil moisture during summer growth, indicating that irrigation scheduling must account for seasonal shifts in cover-crop water use.

The most effective optimization strategy is to combine cover crops with targeted nutrient management rather than treating grassing as a standalone practice. In hilly citrus orchards, the optimized system integrating cover crops with reduced chemical fertilizer and organic fertilizer achieved both lower carbon and water footprints and higher yield and profit than chemical fertilizer alone, showing that coordinated nutrient regulation can turn ecological benefits into agronomic gains (Ning et al., 2026). This integrated approach is especially important where long-lived covers deplete available nutrients: high-altitude orchard evidence showed that perennial artificial grass systems increased total ecosystem service value but reduced supporting services through lower available phosphorus and potassium, so supplemental fertilization was recommended to maintain long-term productivity.

8.3 Long-term effects and challenges in the application and extension of grass cover cultivation

Long-term evidence shows that many benefits of grass cover accumulate over time, but it also reveals why adoption remains uneven. Meta-analysis in citrus orchards found that grass age and growth mode were major determinants of soil carbon and nitrogen gains, and responses were stronger when cover persisted for at least 10 years and was applied across the whole orchard. A second meta-analysis across Chinese orchards similarly showed that SOC gains depended strongly on grass age, with longer than 12 months of cultivated grass cover in mature orchards being especially effective, confirming that short trials can underestimate the value of grassing (Xiang et al., 2021).

The challenge for extension is that long-term benefits are real but not always immediately visible to growers, and performance varies sharply by region and management context. Recent citrus field work emphasized a short-term “lag effect,” with significant changes in soil moisture, available nutrients, and CO₂ flux occurring within two years but no detectable yield or fruit-quality response over that period. Adoption is also constrained by grower concerns over competition and by regional variation in climate, soil, and tree type, even though long-term assessments indicate that orchard grass generally improves yield, quality, soil health, and economic returns modestly over clear tillage (Ren et al., 2022). Overall, the optimization of grass cover cultivation in citrus orchards depends on choosing species by site, coordinating cover with irrigation and fertilization, and evaluating outcomes over sufficiently long periods. The most transferable strategy is not maximum cover, but adaptive cover management that preserves soil and ecosystem benefits while limiting competition with citrus trees.

9 Conclusions and Future Perspectives

Grass cover cultivation improves soil fertility in citrus orchards primarily by increasing organic matter inputs and strengthening nutrient retention within the soil profile. Aboveground residues, root turnover, and rhizosphere deposition continuously return carbon-rich materials to the soil, promoting the accumulation of soil organic carbon and total nitrogen, especially in surface layers. At the same time, grass cover reduces runoff, erosion, and sediment-associated nutrient loss, which helps conserve nitrogen, phosphorus, and potassium in orchard soils. These effects are particularly important in sloping citrus orchards and other erosion-prone environments, where bare ground management often accelerates nutrient depletion and soil degradation. A second major mechanism is the stimulation of soil biological processes that regulate nutrient cycling and soil structural development. Grass cover generally increases microbial biomass, microbial diversity, and the activity of key soil enzymes involved in carbon, nitrogen, and phosphorus turnover, thereby accelerating the transformation of organic residues into plant-available nutrients. Improved aggregate formation and greater aggregate stability further protect organic matter from rapid loss and create a more favorable habitat for beneficial microorganisms. In legume-based or mixed cover systems, biological nitrogen fixation can further enrich soil nitrogen pools, while long-term cover management tends to strengthen these biological and biochemical benefits more clearly than short-term establishment.

Beyond soil fertility, grass cover cultivation plays an important role in enhancing the ecological stability of citrus orchards. By protecting the soil surface, moderating temperature and moisture fluctuations, and reducing the physical disturbance associated with clean tillage, grass cover helps maintain more stable environmental conditions for both roots and soil biota. It also supports more complex microbial communities and stronger ecological interactions in the soil, which contributes to greater functional resilience under environmental stress. At the orchard scale, these improvements translate into better resistance to erosion, stronger water-holding capacity, and more stable nutrient cycling processes. Grass cover also promotes ecosystem stability by increasing the multifunctionality of citrus orchards. In addition to improving soil quality, it can support biodiversity, suppress weeds, reduce non-point source pollution, and contribute to carbon sequestration and broader regulating services. However, these benefits are not uniform across all systems. The stability gains from grass cover depend strongly on grass species, coverage pattern, orchard age, rainfall regime, and soil fertility background. In water-limited environments or under excessive full-cover competition, grassing can reduce shallow soil moisture and suppress fruit yield, which means that ecosystem stabilization should be understood as a managed balance between conservation benefits and tree resource demand rather than as a universally positive effect.

Future research should place greater emphasis on long-term, site-specific, and mechanism-oriented evaluation of grass cover systems in citrus orchards. Many existing studies confirm clear improvements in soil nutrients, microbial activity, and erosion control, but the magnitude and persistence of these effects vary widely across climates, soils, and management regimes. Longer monitoring periods are needed to distinguish short-term responses from stable long-term trends, especially in perennial orchard systems where changes in tree growth, yield, and fruit quality may lag behind early improvements in soil condition. More attention should also be given to how grass biomass production, root traits, residue quality, and seasonal growth dynamics influence soil carbon sequestration, nitrogen transformation, and nutrient availability. A second priority is the development of integrated management strategies that combine grass cover with irrigation, fertilization, mowing, and species selection. Future studies should compare natural grass, legumes, grasses, and mixed cover systems under different production objectives to identify combinations that best balance soil improvement, ecological services, and economic return. Greater focus is also needed on drought competition, nutrient depletion under long-term perennial cover, and the adaptation of grass-cover systems to disease-affected orchards and fragile environments. Ultimately, future work should move beyond evaluating whether grass cover is beneficial in general and instead determine which cover system is most suitable for specific citrus production regions, so that grass cover cultivation can be translated from a conservation practice into a reliable component of sustainable orchard management. Overall, grass cover cultivation improves soil fertility in citrus orchards through organic matter accumulation, biological activation, and loss reduction, while its ecological value depends on adaptive management. Future progress will depend on designing regionally matched grass-cover systems that strengthen both soil health and long-term orchard sustainability.

Acknowledgments

I extend my sincere gratitude to the anonymous reviewers for their valuable and insightful comments, which have greatly strengthened this paper.

Conflict of Interest Disclosure

The author affirms that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.

References

Brewer M., Strauss S.L., Kanissery R.G., and Kadyampakeni D.M., 2025, The impacts of legume and non-legume cover crops on the performance of HLB-affected citrus trees, Journal of Plant Nutrition, 48(13): 2235-2249.

https://doi.org/10.1080/01904167.2025.2474031

Capri C., Gatti M., Fiorini A., Ardenti F., Tabaglio V., and Poni S., 2023, A comparative study of fifteen cover crop species for orchard soil management: water uptake, root density traits and soil aggregate stability, Scientific Reports, 13(1): 721.

https://doi.org/10.1038/s41598-023-27915-7

Castellano-Hinojosa A., Kanissery R.G., and Strauss S.L., 2023, Cover crops in citrus orchards impact soil nutrient cycling and the soil microbiome after three years but effects are site-specific, Biology and Fertility of Soils, 59(6): 659-678.

https://doi.org/10.1007/s00374-023-01729-1

Castellano-Hinojosa A., Martens-Habbena W., Smyth A.R., Kadyampakeni D., and Strauss S.L., 2021, Short-term effects of cover crops on soil properties and the abundance of N-cycling genes in citrus agroecosystems, Applied Soil Ecology, 172: 104341.

https://doi.org/10.1016/j.apsoil.2021.104341

Chakravarty S., and Wade T., 2023, Cost analysis of using cover crops in citrus production, HortTechnology, 33(3): 278-285.

https://doi.org/10.21273/horttech05126-22

Chen L., Bao Y., He X., Yang J., Wu Q., and Lv J., 2025, Nature-based accumulation of organic carbon and nitrogen in citrus orchard soil with grass coverage, Soil and Tillage Research, 248: 106419.

https://doi.org/10.1016/j.still.2024.106419

De Pedro L., Perera-Fernández L., López-Gallego E., Pérez-Marcos M., and Sanchez J., 2020, The effect of cover crops on the biodiversity and abundance of ground-dwelling arthropods in a Mediterranean pear orchard, Agronomy, 10(4): 580.

https://doi.org/10.3390/agronomy10040580

Demestihas C., Plénet D., Génard M., Raynal C., and Lescourret F., 2017, Ecosystem services in orchards. a review, Agronomy for Sustainable Development, 37(2): 12.

https://doi.org/10.1007/s13593-017-0422-1

Deng L., Pan Y., Li H., Wu L., Wang C., Liu D., Zhang J., Cheng J., Song F., and Pan Z., 2026, Cover cropping enhances fruit quality in protected citrus cultivation by modulating rhizosphere microbiome and iron availability, Frontiers in Plant Science, 17: 1836783.

https://doi.org/10.3389/fpls.2026.1836783

Judt C., Korányi D., Zaller J.G., and Batáry P., 2023, Floral resources and ground covers promote natural enemies but not pest insects in apple orchards: a global meta-analysis, Science of the Total Environment, 903: 166139.

https://doi.org/10.1016/j.scitotenv.2023.166139

Liu R., Zhang Y., Wang Z., Zhang X., Xu W., Zhang J., Zhang Y., Hu B., Shi X., and Rennenberg H., 2024, Groundcover improves nutrition and growth of citrus trees and reduces water runoff, soil erosion and nutrient loss on sloping farmland, Frontiers in Plant Science, 15: 1489693.

https://doi.org/10.3389/fpls.2024.1489693

Martinelli R., Monquero P.A., Fontanetti A., Conceição P.M., and Azevedo F.A., 2017, Ecological mowing: an option for sustainable weed management in young citrus orchards, Weed Technology, 31(2): 260-268.

https://doi.org/10.1017/wet.2017.3

Ning W., Zhao J., Lakshmanan P., Wang S., Ran Y., He T., Zhan P., Wang Z., Ye S., Xiang Y., Wen Y., Shi X., Zhao J., and Zhang Y., 2026, Co-benefits of reduced carbon and water footprints and enhanced carbon sequestration with integrated organic–inorganic fertilization and cover cropping in hilly citrus orchards, Frontiers in Plant Science, 17: 1763629.

https://doi.org/10.3389/fpls.2026.1763629

Pantigoso H.A., Newberger D.R., and Vivanco J.M., 2022, The rhizosphere microbiome: Plant–microbial interactions for resource acquisition, Journal of Applied Microbiology, 133(5): 2864-2876.

https://doi.org/10.1111/jam.15686

Ren J., Li F., and Yin C., 2022, Orchard grass safeguards sustainable development of fruit industry in China, Journal of Cleaner Production, 382: 135291.

https://doi.org/10.1016/j.jclepro.2022.135291

Shi C.-H., Wang X.-Q., Jiang S., Xu J., and Luo J., 2024, Investigating the impact of long-term bristlegrass coverage on rhizosphere microbiota, soil metabolites, and carbon–nitrogen dynamics for pear agronomic traits in orchards, Frontiers in Microbiology, 15: 1461254.

https://doi.org/10.3389/fmicb.2024.1461254

Shimizu G.D., Paula J.C.B., Silva A.P.D., Pacheco C.D.A., Azevedo F.A., Gonçalves L., and Neves C.S.V.J., 2022, Chemical and microbiological changes in the soil mediated by different vegetative coverings in a Natal orange orchard, Semina: Ciências Agrárias, 43(1): 331-348.

https://doi.org/10.5433/1679-0359.2022v43n1p331

Silwana S., Mulidzi A.R., and Jovanović N., 2023, Evaluating the effects and benefits of cover crops in citrus orchards: a review, South African Journal of Plant and Soil, 40(2): 117-126.

https://doi.org/10.1080/02571862.2023.2236075

Tamburini G., Aguilera G., and Öckinger E., 2022, Grasslands enhance ecosystem service multifunctionality above and below ground in agricultural landscapes, Journal of Applied Ecology, 59(12): 3061-3071.

https://doi.org/10.1111/1365-2664.14302

Tang R., Li L.J., Guo Y., Yuan R., Feng Y.-T., Wang J., Yu Y., Song H.Y., Zhang J., Wu D., and Xiang G., 2026, Evaluating multi-benefit cover crop management models for citrus sustainable management: a field study from central China, Plants, 15(10): 1479.

https://doi.org/10.3390/plants15101479

Vignozzi N., Agnelli A., Brandi G., Gagnarli E., Goggioli D., Lagomarsino A., Pellegrini S., Simoncini S., Simoni S., Valboa G., Caruso G., and Gucci R., 2019, Soil ecosystem functions in a high-density olive orchard managed by different soil conservation practices, Applied Soil Ecology, 134: 64-76.

https://doi.org/10.1016/j.apsoil.2018.10.014

Visconti F., Peiró E., Baixauli C., and De Paz J.D., 2022, Spontaneous plants improve the inter-row soil fertility in a citrus orchard but nitrogen lacks to boost organic carbon, Environments, 9(12): 151.

https://doi.org/10.3390/environments9120151

Wang J., Qin X., Tan Y., Du Y., Tudi Y., Yang Y., and Ping X., 2024, Impact of grass cover on the soil physicochemical properties in China’s orchards: a meta-analysis, Agroforestry Systems, 98(6): 1745-1758.

https://doi.org/10.1007/s10457-024-00985-w

Wang N., Li L., Gou M., Hu J., Chen H., Xiao W., and Liu C., 2024, Leguminous green mulching alters the microbial community structure and increases microbial diversity by improving nitrogen availability in subtropical orchard systems in China, Science of the Total Environment, 955: 176891.

https://doi.org/10.1016/j.scitotenv.2024.176891

Wang N., Li L., Gou M., Jian Z., Hu J.J., Chen H., Xiao W., and Liu C., 2022, Living grass mulching improves soil enzyme activities through enhanced available nutrients in citrus orchards in subtropical China, Frontiers in Plant Science, 13: 1053009.

https://doi.org/10.3389/fpls.2022.1053009

Wang Y., Liu L., Yang J., Duan Y., Luo Y., Taherzadeh M.J., Li Y., Li H., Awasthi M.K., and Zhao Z., 2020, The diversity of microbial community and function varied in response to different agricultural residues composting, Science of the Total Environment, 715: 136983.

https://doi.org/10.1016/j.scitotenv.2020.136983

Wu Y.-P., Wang X., Hu R., Zhao J., and Jiang Y., 2021, Responses of soil microbial traits to ground cover in citrus orchards in central China, Microorganisms, 9(12): 2507.

https://doi.org/10.3390/microorganisms9122507

Xiang Y., Chang S.X., Shen Y., Chen G.Z., Liu Y., Yao B., Xue J., and Li Y., 2023, Grass cover increases soil microbial abundance and diversity and extracellular enzyme activities in orchards: a synthesis across China, Applied Soil Ecology, 182: 104720.

https://doi.org/10.1016/j.apsoil.2022.104720

Xu Q., Wang T., Cai C., Li Z.X., and Shi Z.H., 2010, Effects of soil conservation on soil properties of citrus orchards in the Three-Gorges Area, China, Land Degradation and Development, 23(1): 34-42.

https://doi.org/10.1002/ldr.1045

Zhang J., Lei L., Xiao W., Yang X., Horwath W.R., Liao Y., Yang H., Jian Z., and Zeng L., 2025, Vetch cover crops increase particulate organic carbon in citrus orchard by increasing lignin phenols, Applied Soil Ecology, 207: 105921.

https://doi.org/10.1016/j.apsoil.2025.105921

Zheng J.Y., Zhao J., Shi Z.H., Shi Z.H., Wang L., and Wang L., 2021, Soil aggregates are key factors that regulate erosion-related carbon loss in citrus orchards of southern China: Bare land vs. grass-covered land, Agriculture, Ecosystems and Environment, 309: 107254.

https://doi.org/10.1016/j.agee.2020.107254