How to Increase Arbuscular Mycorrhizal Fungi in Soil

Introduction

Arbuscular mycorrhizal fungi, commonly known as AMF, are beneficial soil fungi that form a natural partnership with plant roots. In this relationship, plants provide the fungi with sugars from photosynthesis, while the fungi help plants access nutrients and water from a larger soil volume.

For growers, increasing arbuscular mycorrhizal fungi in soil can support better root development, improved phosphorus and micronutrient uptake, stronger crop establishment, better drought tolerance, and healthier soil structure. AMF are especially valuable in sustainable agriculture because they improve the biological function of the root zone rather than relying only on soluble fertilizer inputs.

The good news is that growers can actively encourage AMF through practical soil management, crop rotation, reduced disturbance, organic matter improvement, and direct AMF inoculation.

What Are Arbuscular Mycorrhizal Fungi?

Arbuscular mycorrhizal fungi are microscopic fungi that colonize plant roots and extend fine fungal threads, called hyphae, into the surrounding soil. These hyphae act like extensions of the root system, helping plants reach nutrients that would otherwise remain unavailable.

AMF are especially important for phosphorus uptake because phosphorus is often present in soil but moves slowly and becomes fixed in forms that roots cannot easily access. AMF hyphae can explore soil pores beyond the root depletion zone and help deliver phosphorus, nitrogen, zinc, copper, and other nutrients back to the plant.

They also contribute to soil aggregation, water movement, and root-zone stability. In practical terms, crops with strong mycorrhizal associations are often better equipped to handle nutrient limitations, transplant stress, drought, salinity, and other difficult growing conditions.

Why Increasing AMF Matters for Crop Growth

Increasing AMF in soil is not just about adding one more biological input. It is about building a more active and efficient root-zone system.

A healthy AMF population can help:

• Improve phosphorus uptake

• Enhance micronutrient availability

• Increase root absorptive capacity

• Improve soil aggregation

• Support drought tolerance

• Improve transplant establishment

• Reduce nutrient stress

• Support long-term soil fertility

• Improve crop resilience under variable field conditions

AMF work best as part of a complete soil-health program. They need living roots, suitable soil conditions, moderate nutrient levels, and low disturbance to develop properly.

Practical Ways to Increase Arbuscular Mycorrhizal Fungi in Soil

1. Apply a High-Quality AMF Inoculant

The fastest way to increase arbuscular mycorrhizal fungi in soil is to apply a quality AMF inoculant. This is especially useful in soils where AMF populations have been reduced by intensive tillage, fumigation, heavy fertilizer use, poor crop rotation, or long periods without living roots.

AMF inoculants are commonly applied through:

• Seed treatment

• Seed coating

• In-furrow application

• Root dipping

• Transplant hole application

• Soil drench

• Potting mix incorporation

• Nursery and propagation media

The most important rule is root contact. AMF must reach the developing root system to colonize successfully. Applying AMF far away from the root zone reduces the chance of colonization and lowers product efficiency.

For best results, apply AMF at planting, seeding, transplanting, or early root establishment.

2. Reduce Excess Phosphorus Fertilizer

High levels of readily available phosphorus can suppress mycorrhizal colonization. When plants have easy access to large amounts of soluble phosphorus, they may reduce their dependence on AMF.

This does not mean phosphorus should be removed completely. Crops still need balanced nutrition. However, excessive phosphorus applications can reduce the biological benefit of AMF.

A practical approach is to:

• Test soil before applying phosphorus

• Avoid unnecessary high-P fertilizer programs

• Use moderate phosphorus rates

• Place phosphorus strategically

• Allow AMF to help access existing soil phosphorus

• Combine AMF with phosphate-solubilizing microbes where appropriate

AMF are most valuable when phosphorus is present but not easily available to the plant.

3. Minimize Soil Disturbance

Intensive tillage damages AMF hyphal networks. These fungal networks take time to develop in soil, and repeated deep cultivation can break them apart before they deliver full benefits.

To support AMF:

• Reduce deep tillage where possible

• Use strip-till, no-till, or minimum-till systems when suitable

• Avoid unnecessary cultivation passes

• Keep soil structure intact

• Protect root-zone fungal networks between crops

Lower disturbance helps AMF survive between growing seasons and allows fungal networks to reconnect quickly with new crop roots.

4. Keep Living Roots in the Soil

AMF depend on living plants. They are obligate symbionts, meaning they need plant hosts to complete their life cycle and remain active. Long periods of bare soil can reduce AMF populations.

To increase AMF, avoid leaving fields empty for long periods. Instead, use:

• Cover crops

• Relay cropping

• Intercropping

• Living mulches where appropriate

• Diverse crop rotations

• Perennial strips or border vegetation

Living roots feed AMF and help maintain active fungal networks in the soil.

5. Grow AMF-Friendly Crops

Most crops form mycorrhizal associations, but not all plants are good AMF hosts. Many cereals, legumes, grasses, fruit crops, vegetables, herbs, and ornamentals support AMF well.

Good AMF host crops include:

• Maize

• Wheat

• Sorghum

• Millet

• Soybean

• Beans

• Peas

• Tomato

• Pepper

• Onion

• Garlic

• Fruit trees

• Grapevines

• Grasses

• Many herbs and flowers

Some crops, especially many members of the Brassicaceae family, do not form strong AMF associations. These include cabbage, broccoli, cauliflower, mustard, radish, and canola. Growing non-host crops repeatedly may reduce AMF levels in the soil.

A smart rotation includes strong AMF host crops to rebuild fungal populations.

6. Use Cover Crops That Support AMF

Cover crops are one of the best tools for increasing arbuscular mycorrhizal fungi naturally. They keep living roots in the soil during fallow periods and provide a host for AMF between cash crops.

AMF-friendly cover crops include:

• Cereal rye

• Oats

• Wheat

• Barley

• Sorghum-sudangrass

• Clover

• Vetch

• Peas

• Cowpea

• Buckwheat

• Grasses and legumes in mixed covers

Mixed cover crops are often more effective than single-species covers because they support a more diverse soil microbial community.

Avoid relying only on brassica cover crops if the goal is to build AMF. Brassicas can be useful for other reasons, but they are generally not strong AMF hosts.

7. Add Organic Matter and Compost

Organic matter supports the wider soil food web, improves soil structure, and creates better conditions for AMF development. Compost, manure, crop residues, and organic amendments can improve soil biological activity and moisture retention.

However, compost quality matters. Use mature, well-processed compost rather than unstable or overly salty material. Excess salts, poor aeration, or contaminated compost can reduce microbial performance.

Good organic matter management helps AMF by improving:

• Soil moisture balance

• Aggregation

• Root growth

• Microbial diversity

• Nutrient cycling

• Soil structure

• Carbon availability in the root zone

AMF benefit from a biologically active soil environment.

8. Avoid Unnecessary Fungicide Pressure

AMF are fungi. Some fungicides, fumigants, disinfectants, and harsh chemical treatments can reduce AMF activity, especially when applied directly to soil or seed.

This does not mean every fungicide will eliminate AMF, but unnecessary or poorly timed applications can reduce colonization and fungal survival.

To protect AMF:

• Avoid soil fumigation unless absolutely necessary

• Check fungicide compatibility with AMF inoculants

• Avoid mixing AMF directly with incompatible fungicides

• Separate biological applications from harsh chemical treatments

• Use integrated disease management rather than routine overuse

When chemical disease control is needed, plan the timing carefully so AMF can still establish.

9. Maintain Good Soil Moisture

AMF need suitable moisture to grow, colonize roots, and move nutrients. Extremely dry soil can slow fungal activity, while waterlogged soil can reduce oxygen and harm root function.

The goal is balanced moisture.

To support AMF:

• Avoid prolonged drought stress

• Improve water infiltration with organic matter

• Use mulch where appropriate

• Avoid compaction and poor drainage

• Irrigate consistently during establishment

• Prevent waterlogging in heavy soils

Healthy roots and active AMF both depend on good soil air-water balance.

10. Reduce Soil Compaction

Compacted soil restricts root growth, reduces pore space, limits oxygen, and makes it harder for fungal hyphae to spread. AMF perform best in soils with good structure.

To reduce compaction:

• Avoid working wet soil

• Use controlled traffic where possible

• Add organic matter

• Use deep-rooted cover crops

• Reduce unnecessary machinery passes

• Improve drainage

• Maintain stable soil aggregates

Better soil structure supports both roots and AMF networks.

11. Combine AMF with Beneficial Microbes

AMF often work well with other beneficial microorganisms. They can be combined with phosphate-solubilizing bacteria, nitrogen-fixing bacteria, Bacillus species, Pseudomonas species, Trichoderma, and other root-zone microbes when compatibility is confirmed.

A strong microbial program may include:

• AMF for root extension and nutrient uptake

• Phosphate-solubilizing bacteria for phosphorus release

• Nitrogen-fixing bacteria for biological nitrogen support

• Bacillus species for stress tolerance and formulation resilience

• Trichoderma for root-zone protection and organic matter transformation

The best results come from compatible microbial consortia, not random mixing. Always check product compatibility and application instructions.

12. Apply AMF Early in the Crop Cycle

AMF need time to colonize roots and build hyphal networks. Late application may still help in some systems, but early application gives the fungi more time to support the crop.

Best timing includes:

• Seed treatment before sowing

• In-furrow at planting

• Root dip before transplanting

• Transplant hole application

• Early vegetative stage

• Nursery and propagation stage

For perennial crops, apply AMF during planting, root flushing, or active root growth periods.

13. Avoid Long Bare Fallow Periods

Bare fallow reduces living root activity and can lower AMF populations. Fields left without host plants for long periods often lose biological activity.

Instead of bare fallow:

• Use cover crops

• Maintain crop residues

• Grow short-season hosts

• Keep perennial ground covers in orchards where practical

• Use living root systems between cash crops

This keeps AMF active and ready for the next crop.

14. Use AMF in Nursery and Transplant Production

AMF can be especially valuable in nurseries, plug trays, and transplant systems. Early colonization helps seedlings establish stronger root systems before field planting.

AMF can be applied to:

• Plug trays

• Potting mixes

• Nursery beds

• Transplant roots

• Tree seedlings

• Vegetable transplants

• Ornamental plants

The key is placing AMF close to roots and avoiding sterilized or high-phosphorus media that suppress colonization.

15. Monitor Results and Adjust Management

AMF success is not always visible immediately. Colonization takes time, and benefits may appear as improved root growth, better nutrient efficiency, stronger drought tolerance, or healthier crop establishment.

To evaluate progress:

• Compare treated and untreated areas

• Monitor root development

• Track phosphorus fertilizer response

• Watch crop vigour during stress periods

• Test soil nutrients

• Check root colonization through lab analysis where possible

• Record yield and quality data

Over time, AMF-friendly management can improve soil biological function and reduce dependence on heavy input correction.

Common Mistakes That Reduce AMF

Avoid these common mistakes:

• Applying AMF without root contact

• Using very high phosphorus fertilizer rates

• Leaving soil bare for long periods

• Repeated intensive tillage

• Applying incompatible fungicides

• Growing non-host crops too frequently

• Storing AMF products in heat or sunlight

• Applying expired or poor-quality inoculants

• Using AMF in waterlogged or highly compacted soil

• Expecting instant results without soil-health management

AMF are powerful biological partners, but they need the right conditions to work.

FAQs

How can I increase arbuscular mycorrhizal fungi in soil?

You can increase arbuscular mycorrhizal fungi by applying AMF inoculants, growing AMF-friendly crops, using cover crops, reducing tillage, avoiding excessive phosphorus fertilizer, improving organic matter, maintaining soil moisture, and keeping living roots in the soil.

What is the fastest way to boost AMF in soil?

The fastest way is to apply a high-quality AMF inoculant directly to the seed, transplant roots, or

root zone. Direct root contact is essential for successful colonization.

Do cover crops increase AMF?

Yes. AMF-friendly cover crops such as grasses, cereals, legumes, and mixed cover crop blends can support AMF populations by keeping living roots in the soil between cash crops.

Does tillage reduce AMF?

Yes. Intensive tillage can break AMF hyphal networks and reduce fungal activity. Minimum tillage or reduced tillage helps preserve mycorrhizal networks.

Does phosphorus fertilizer affect AMF?

Yes. Excessive readily available phosphorus can suppress AMF colonization because plants become less dependent on the fungal partnership. Balanced phosphorus management supports better AMF activity.

Which crops support AMF?

Many crops support AMF, including maize, wheat, soybean, beans, peas, tomato, pepper, onion, garlic, fruit trees, grapevines, and many grasses and herbs.

Which crops do not support AMF well?

Many Brassicaceae crops, such as cabbage, broccoli, cauliflower, mustard, radish, and canola, do not form strong mycorrhizal associations. Repeated brassica-heavy rotations may reduce AMF levels.

Can AMF be used with compost?

Yes. Compost and organic matter can improve soil conditions for AMF. However, compost should be mature, stable, and not overly salty.

Can AMF be mixed with other biofertilizers?

Yes. AMF can be used with compatible beneficial microbes such as phosphate-solubilizing bacteria, nitrogen-fixing bacteria, Bacillus, Pseudomonas, and Trichoderma. Compatibility should be confirmed before mixing.

How long does AMF take to work?

AMF colonization usually begins within a few weeks under suitable conditions. Visible benefits may take longer and often become more noticeable during nutrient stress, drought stress, transplanting, or later crop development.

Conclusion

Increasing arbuscular mycorrhizal fungi in soil is one of the most practical ways to improve root-zone biology and support better crop growth. AMF help plants access phosphorus, micronutrients, and water while improving soil aggregation and resilience.

The best results come from combining direct AMF inoculation with AMF-friendly farming practices: reduce tillage, avoid excessive phosphorus, grow host crops and cover crops, maintain organic matter, protect soil moisture, and avoid unnecessary fungicide pressure.

When AMF are supported properly, they become a long-term biological asset in the soil, helping growers build stronger crops and healthier farming systems.

Build Stronger Root Systems with IndoGulf BioAg AMF Solutions

Looking to improve root growth, nutrient uptake, and soil biology with arbuscular mycorrhizal fungi?

IndoGulf BioAg develops and supplies advanced AMF products and custom microbial formulations for agriculture, horticulture, nursery production, and private-label programs. Contact our team today to discuss AMF inoculants, crop-specific application strategies, and biological root-zone solutions for your market.