Mycorrhizal Fungi Under No-Till

Arbuscular Mycorrhizal Fungi (AMF) form symbiotic relationships with plant roots, facilitating nutrient uptake — especially phosphorus — in exchange for carbohydrates. Population diversity and abundance is significantly greater under direct seeding than under ploughing.

Overview

  • ~80% of plants benefit from mycorrhizal fungi symbiosis
  • AMF facilitate access to: phosphorus (primary), nitrogen, water
  • Mechanism: hyphae access pores too small for plant roots
  • ~270 AMF species investigated worldwide
  • Considered bioindicators of good agricultural soils

[Source: dd-issue-01, 2026-04-11]

The Oberacker Trial — 20-Year Comparison

Site: Oberacker, Zollikofen, Switzerland — deep brown soil Duration: Since 1994 (20+ years at time of publication) Design: 6 adjacent parcels, half no-till / half ploughed Crop rotation: 6-year — winter pea, winter wheat, beans, winter barley, sugar beet, maize silage Sampling: February 2011, 0–10cm depth, 20 samples per sub-parcel

Species Richness Results

System Total AMF species identified Range per plot
No-till (direct seeding) 38 15–21
Ploughed 25 10–17

Average species count: 18.5 (no-till) vs 13.2 (ploughed) — significantly higher under no-till.

[Source: dd-issue-01, 2026-04-11]

Diversity Index (Shannon H)

System Diversity Index H
No-till 2.49 (range 2.12–2.86)
Ploughed 2.17 (range 1.77–2.56)

Comparable to organic cultivation or grassland values for no-till plots.

[Source: dd-issue-01, 2026-04-11]

Species Groups

Group Description Count
A (grey) Present regularly in both systems 13 species
B (green) Primarily/exclusively no-till; high spore density 11 species
C (yellow) Primarily/exclusively no-till; low spore density; typical of grassland/extensive land 13 species
D (brown) Primarily/exclusively ploughed plots 2 species

24 out of 39 species found primarily or exclusively under no-till.

[Source: dd-issue-01, 2026-04-11]

Indicator Species

System Characteristic species
Long-term no-till Septoglomus constrictum
Ploughed Funneliformis caledonius

Septoglomus constrictum is an indicator species for long-term direct seeding at Oberacker.

[Source: dd-issue-01, 2026-04-11]

What Drives AMF Community Composition

Variables with greatest individual influence:

  1. Organic carbon in soil (Corg)
  2. Cropping system (no-till vs ploughed)
  3. Microbial mass

Chemical parameters: Corg and pH were significant. The cropping system effect is partly indirect — through its effect on surface Corg (higher in top 10cm under no-till).

[Source: dd-issue-01, 2026-04-11]

Crop Effects on AMF Diversity

  • Winter protein peas: highest species count (21 no-till / 17 ploughed)
  • Winter wheat: moderate (17/15)
  • Winter barley: lowest (15/11)
  • Sugar beet: lowest count — sugar beet is non-mycorrhizal and mechanically disturbs top 10cm at harvest
  • Under ploughing: effect persistent (soil regularly disturbed)
  • Under no-till: number of species remains high despite beet — the fungal network is resilient

[Source: dd-issue-01, 2026-04-11]

General Principle: Land Use and Intensity

  • Grasslands > crops for AMF diversity
  • Extensive cropping > intensive rotations
  • Uncultivated soil > cultivated soil
  • Long-term no-till moves toward grassland-equivalent AMF diversity

Significance for Direct Drilling

High AMF diversity under no-till:

  • Improves phosphorus uptake → reduces P fertiliser requirement
  • Better nitrogen and water availability through hyphae network
  • More stable plant-fungi relationships
  • Characteristic grassland species colonise no-till fields over time

[Source: dd-issue-01, 2026-04-11]

Wheat Variety AMF Colonisation Trial (Essex, 2017)

Trial run by Lottie Alves (Procam) on a long-term no-till farm in Essex with confirmed high background AMF levels.

Trial design: 9 wheat varieties + farmer’s own Group 4 blend; drilled autumn 2016 following lucerne; root samples stained and assessed in March (tillering) and July (pre-harvest).

Finding: All modern varieties can form AMF associations, but colonisation levels vary significantly between varieties.

Variety Ranking

Timing Most mycorrhizal Second
March KWS Silverstone (2–5× other varieties) KWS Bassett
July KWS Bassett KWS Silverstone

[Source: dd-issue-02, 2026-04-11]

Key observations:

  • KWS Silverstone at March sampling had double to five times the colonised root area of other varieties — a large early advantage
  • By July, less mycorrhizal varieties “catch up” as AMF becomes more active with rising temperatures
  • KWS Bassett led at July timing, KWS Silverstone still second
  • Conclusion: KWS Bassett and KWS Silverstone potentially the best varieties for no-till systems with established AMF populations

Second-year trial ongoing at time of publication (2018); Procam presenting preliminary year-two results at Groundswell 2018, Stand E5.

See also Wheat Varieties and Mycorrhizal Fungi for the full trial page.

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