Multi-dimensional role of green manuring crops in enhancing soil health and ecosystem functions: A comprehensive review

Introduction

Modern intensive agriculture and heavy reliance on synthetic fertilizers have led to severe soil health degradation, particularly in heavily cropped regions like the Indo-Gangetic plains (Mandal et al., 2003) [12] . Green manuring is a core management strategy in conservation agriculture. The system involves growing specialized cover crops-primarily fast-growing legumes or deep-rooted crucifers and incorporating their succulent green biomass directly into the soil plough layer during the pre-flowering stage. This technique restores soil fertility, recaptures deep-seated nutrients, stimulates multi-trophic biological webs, and builds resilient physical soil structures without relying on synthetic inputs. The soil rhizosphere-the narrow zone of soil directly influenced by root secretions and associated microorganisms is the primary hot spot for nutrient transformation and uptake in agricultural systems (Richardson et al., 2009) [17] . Traditional intensive cropping often depletes rhizosphere organic substrates, resulting in degraded biological activity. Green manuring bridges the gap between biological activity and chemical nutrient availability within the rhizosphere (Fageria, 2007) [3] .

Importance of green manuring in enhancing soil health and ecosystem functions: 1. Physical properties of soil 1.1 Soil Aggregation and Structure

The addition of green manure biomass contributes readily decomposable organic carbon to the soil matrix (Sahil et al., 2026) [5] . As soil microbes decompose this fresh material, they exude polysaccharides, mucilages, and other microbial binding agents that glue individual soil particles together into structural units (MacRae & Mehuys, 1988) [11] . This process significantly enhances water-stable soil aggregation and improves overall structural stability (Dabney et al., 2001) [2] . Stable aggregates prevent the formation of hard surface crusts, which otherwise impede seedling emergence and restrict rainfall intake (Mavi & Singh, 2007) [13] .

Reduction of Soil Bulk Density

High soil bulk density restricts root proliferation and limits fluid movement through the soil profile (Shukla et al., 2004) [18] . Green manuring consistently decreases soil bulk density by increasing the volume of total pore space (Mandal et al., 2003) [12] . The rapid accumulation and sub-surface incorporation of high-volume organic biomass lower the soil's compacted state (Rathika et al., 2026) [16] . This results in a looser, more friable soil tilth that reduces mechanical impedance for subsequent cash crops (Mavi & Singh, 2007) [13] .

Moisture Retention and Water Dynamics

Improving soil organic matter (SOM) fractions directly influences the soil-water relationship (Dabney et al., 2001) [2] . Green-manured soils exhibit an increased water-holding capacity, which provides distinct physical benefits for both light-textured sandy soils and heavy clay soils (MacRae & Mehuys, 1988) [11] . In sandy soils, the added organic matter acts like a sponge to retain water against gravity, while in clay soils, improved aggregation increases the number of transmissions macropores for better drainage (Shukla et al., 2004) [18] . Additionally, increased infiltration rates minimize surface runoff and drastically decrease topsoil erosion risks (Dabney et al., 2001) [2] .

Aeration and Thermal Regulation

Root systems of green manure crops, particularly deeprooted legumes, play a vital biological role in disrupting compacted subsurface hardpans by creating extensive bio pores (Rathika et al., 2026) [16] . This enhances soil macroporosity and improves aeration, allowing necessary gas exchange (O₂ and CO₂) between the root zone and the atmosphere (Mandal et al., 2003) [12] . Furthermore, maintaining a green manure canopy cover prior to incorporation buffers extreme soil temperature fluctuations, which protects the soil's microbial populations and minimizes evaporative water loss from the surface layer (Sahil et al., 2026) [5] .

Chemical properties of soil and nutrient cycling

The incorporation of green manures triggers an immediate shift in rhizosphere chemistry, primarily driven by microbial stimulation (Tejada et al., 2011) [19] .

Organic Acid Exudation:

Decomposing green manures release low-molecular-weight organic acids, such as citric, oxalic, and malic acids, which temporarily lower rhizosphere pH and chelate metal cations (Richardson et al., 2009) [17] .

Enzymatic Amplification:

The influx of easily degradable substrates stimulates microbial synthesis of critical extracellular enzymes, including phosphatases, glucosidases, and ureases (Tejada et al., 2011, Kusum, A. 2023) [19,6] .

Siderophore Production:

Enhanced microbial activity promotes the secretion of iron-chelating siderophores, making trace elements more bioavailable to subsequent crops (Richardson et al., 2009) [17] .

Nitrogen Cycling and Biological Nitrogen Fixation (BNF)

Leguminous green manures introduce atmospheric nitrogen into the system via symbiotic fixation, dramatically altering nitrogen availability (Fageria, 2007) [3] .

 Mineralisation and Immobilisation: Fresh biomass with a low carbon-to-nitrogen (C:N) ratio (typically below 20:1) undergoes rapid mineralisation, converting organic nitrogen into plant-available ammonium (NH₄⁺) and nitrate (NO₃⁻) (Fageria, 2007) [3] .  Nitrogen Priming Effect: The supply of labile carbon stimulates indigenous soil microbes to decompose older, recalcitrant soil organic matter, unlocking further nitrogen stores through a process known as the priming effect (Kuzyakov, 2010) [10] .  Leaching Mitigation: Deep-rooted non-leguminous green manures act as "catch crops," absorbing residual profile nitrates and storing them in organic form to prevent groundwater leaching (Tiemann et al., 2015) [20] .

Phosphorus Solubilization and Mobilization

Phosphorus (P) is highly prone to fixation as insoluble complexes in both acidic and alkaline soils, but green manuring acts as a key biochemical driver for its mobilization (Bünemann et al., 2011) [1] . [17,7] .  Phosphatase Activity: Microbial proliferation boosts acid and alkaline phosphatase activity, hydrolysing organic phosphorus forms into orthophosphates (Bünemann et al., 2011) [1] .  Mycorrhizal Symbiosis: Green manure crops support a robust network of Arbuscular Mycorrhizal Fungi (AMF) that extend the root surface area for active phosphorus mining (Richardson et al., 2009) [17] .

Potassium and Micronutrient Dynamics

Beyond N and P, green manures actively redistribute potassium (K) and micro-elements within the root zone through enhanced crop diversity (Tiemann et al., 2015) [20] .  K Bio-accumulation: Green manures act as potassium pumps, taking up K from deeper soil layers and depositing it into the topsoil upon incorporation (Fageria, 2007) [3] .  Micronutrient Complexation: The breakdown products of green manures form stable, soluble organometal complexes with zinc (Zn), iron (Fe), copper (Cu), and manganese (Mn), preventing their fixation into unavailable mineral phases ( [17,9,10] .

Biological properties of soil 3.1 Augmentation of Microbial Biomass Carbon and Nitrogen

The absolute size of the soil microbial pool is a sensitive indicator of overall soil quality and fertility.

Labile Carbon Substrates:

Freshly incorporated green manures bypass the slower breakdown pathways of woody residues. They provide an immediate supply of watersoluble carbohydrates, amino acids, and organic acids that fuel rapid microbial reproduction (Tejada et al., 2011) [19] .

Elevated Biomass Indices:

This resource influx triggers a sharp increase in Soil Microbial Biomass Carbon (SMBC)

and Microbial Biomass Nitrogen (SMBN), creating a larger biological nutrient reservoir that prevents nutrient leaching (Frasier et al., 2016) [4] .

3.4

The "Priming Effect": The sudden rise in active microbial populations temporarily accelerates the decomposition of native, recalcitrant soil organic matter, releasing trapped elements back into the biological cycle (Kuzyakov, 2010) [10] .

Structural Shifts in Soil Microbial Communities

Green manuring does not just increase microbial numbers; it alters the taxonomic and functional composition of the entire soil microbiome.  Bacterial vs. Fungal Succession: The early phases of green manure decomposition favour fast-growing, copiotrophic bacteria (like Proteobacteria and Bacteroidetes). As the remaining residues become tougher and more fibrous, the succession shifts to saprophytic fungi and actinobacteria capable of degrading lignin and cellulose (Tiemann et al., 2015) [20] .  Mycorrhizal Support: Crops utilized as green manures (e.g., specific clovers and legumes) serve as host plants that maintain and build up indigenous populations of Arbuscular Mycorrhizal Fungi (AMF).  Functional Diversity: High-throughput DNA sequencing confirms that green manure rotations significantly increase alpha diversity indices, indicating a more stable, resilient, and redundant microbial network (Zander et al., 2016) [22] .

Amplification of Soil Enzyme Activities

Soil enzymes, secreted primarily by active microbes and plant roots, are the catalysts for almost all biochemical processes in the soil matrix.  Hydrolases and Oxidoreductases: Green manured soils consistently display elevated activities of dehydrogenases, which serve as direct indicators of overall microbial metabolic activity (Tejada et al., 2011) [19] .  Nutrient Target Enzymes: The application of green biomass stimulates the production of specific extracellular enzymes targeting key nutrient pools: βglucosidase for carbon cycling, urease and proteases for nitrogen release, and alkaline/acid phosphatases for unlocking fixed phosphorus (Bünemann et al., 2011) 1[] .

Biological Disease Suppression and Biotherapeutics

Incorporating cover crops and green manures changes the biological equilibrium, transforming the rhizosphere into a hostile environment for soil-borne pathogens.

 Competitive Exclusion: The massive surge in beneficial saprophytic bacteria physically outcompetes pathogens for space, nutrients, and root attachment sites (Mazzola, 2002).  Biofumigation Pathways: Specific green manures release natural chemical compounds upon breakdown. For example, cruciferous green manures (like Brassica juncea) release glucosinolates. When chopped and incorporated, these compounds break down into volatile isothiocyanates, which naturally suppress destructive nematodes, fungi, and weeds (Vandermeer, 1992). [17] Phaseolus trilobus Pillipesera 10.0 -12.0 40 -60 Excellent short-term cover against soil erosion Mavi & Singh (2007) [13]

Some common Green Manure crops applied in soil

Conclusion

Green manuring is an essential nature-based solution, costeffective and ecologically sound strategy for improving soil properties. It helps in continuously building soil organic matter, improving aggregation, decreasing bulk density and regulating soil moisture dynamics. Green manures create a robust, resilient soil environment that sustains long-term crop yields. By integrating root dynamics and fresh plant biomass into the plough layer, this practice recaptures deeplying nutrients and drives critical microbial cycles.

Integrating specific green manures into crop rotations is vital for minimizing synthetic fertilizer inputs and fostering resilient, low-emission agricultural ecosystems.

References

1. Bünemann EK, Oberson A, Frossard E. Phosphorus in action: Biological processes in soil phosphorus cycling. Dordrecht: Springer Science & Business Media; 2011.
2. Dabney SM, Delgado JA, Reeves DW. Using winter cover crops to improve soil and water quality. Commun Soil Sci Plant Anal. 2001;32(7-8):1221-1250.
3. Fageria NK. Green manuring in crop production. J Plant Nutr. 2007;30(5):691-719.
4. Frasier I, Noellemeyer E, Fernandez R, Quiroga A. Direct effects of cover crops on soil microbial biomass and activity. Soil Tillage Res. 2016;159:10-20.
5. Sahil, Garhwal RS, Sumit, Kamboj A, Kumar S. The role of green manures in sustaining soil fertility and crop productivity: A comprehensive review. Int J Plant International Journal of Advanced Biochemistry Research https://www.biochemjournal.com Soil Sci. 2026;38(2):427-439. doi:10.9734/ijpss/2026/v38i25995.
6. Kusum A. Growth dynamics of the epigeic earthworms and microbial activities during different decomposition stages as influenced by food materials [doctoral dissertation]. Raipur: Indira Gandhi Krishi Vishwavidyalaya; 2023.
7. Kusum A, Jha S, Prasad SS, Singh SP. Effect of household waste based vermicompost and fertilizer on phosphorus and potassium mineralization in calcareous soil of Bihar. Int J Chem Stud. 2020;8(1):2094-2098. doi:10.22271/chemi.2020.v8.i1ae.8575.
8. Kusum A, Jha S, Prasad SS, Singh SP. Micronutrient availability as influenced by household waste based vermicompost application in calcareous soil of Bihar during rice growth. Int J Curr Microbiol Appl Sci. 2020;9(2):960-966. doi:10.20546/ijcmas.2020.902.112.
9. Kusum A, Jha S, Prasad SS, Singh SP, Tiwari S. Influence of household waste based vermicompost and fertilizer on micronutrient mineralization in calcareous soil. Plant Sci Today. 2025;12(Suppl):1-7. doi:10.14719/pst.7466.
10. Kuzyakov Y. Priming effects: Interactions between living and dead organic matter. Soil Biol Biochem. 2010;42(9):1363-1371.
11. MacRae RJ, Mehuys GR. The effect of green manuring on the physical properties of temperate-area soils. Adv Soil Sci. 1988;7:71-94.
12. Mandal UK, Singh G, Victor US, Sharma KL. Green manuring: Its effect on soil properties and crop growth. Eur J Agron. 2003;19(2):225-237.
13. Mavi MS, Singh G. Soil physical properties and crop yield as influenced by green manuring. Soil Tillage Res. 2007;92(1-2):110-118.
14. Mazzola M. Mechanisms of natural and induced soil suppressiveness to soilborne diseases. Phytopathology. 2002;92(12):1349-1355.
15. Patra A, Singh RP, Kundu M, Kumar G, Malkani P, Singh B, et al. Green manuring: A sustainable approach for soil health improvement. 2023.
16. Rathika S, Ramesh T, Jeyasrinivas R, Nageswari R, Satheeshkumar N, Sanjaykumar T. Revitalising soil health through green manuring: A sustainable approach. Plant Sci Today. 2026;13(Suppl 5). doi:10.14719/pst.14220.
17. Richardson AE, Barea JM, McNeill AM, PrigentCombaret C. Acquisition of phosphorus and other poorly mobile nutrients by plants. Plant Soil. 2009;321(1-2):305-339.
18. Shukla MK, Lal R, Ebinger M. Tillage effects on physical and hydrological properties of a typic hapludalf in central Ohio. Soil Sci. 2004;169(6):460471.
19. Tejada M, Benítez C, Gómez I, Parrado J. Use of green manures on soil enzymatic activities and wheat yield. Soil Tillage Res. 2011;113(2):115-122.
20. Tiemann LK, Grandy AS, Atkinson EE, Marin-Spiotta E, McDaniel MD. Crop rotational diversity enhances soil organic matter stabilization. Ecol Lett. 2015;18(8):761-771.
21. Vandermeer J. The ecology of intercropping. Cambridge: Cambridge University Press; 1992.
22. Zander P, Amjath-Babu TS, Preissel S, Reckling M. Grain legume expansion in Europe: Sustaining soil biological health. Environ Sci Policy. 2016;62:54-61.