Soil Health · September 2025 · 5 min read
Mycorrhizal fungi form symbiotic relationships with the roots of most crop plants, extending the root system's reach by orders of magnitude. These natural nutrient networks improve phosphorus uptake, drought tolerance, and soil structure. Understanding what helps and harms mycorrhizae allows you to manage them as a valuable biological asset.
Arbuscular mycorrhizal (AM) fungi are the type most relevant to agriculture. They colonize the roots of grasses, legumes, and most broadleaf crops, forming structures called arbuscules inside root cells where nutrient exchange occurs. Ectomycorrhizal (EM) fungi associate primarily with trees and are less important in annual cropping systems.
AM fungi extend microscopic hyphae into soil pores too small for roots, accessing phosphorus and micronutrients that would otherwise be unavailable to the plant.
Mycorrhizal fungi are especially important for phosphorus acquisition. Plants with strong mycorrhizal colonization can access phosphorus from a soil volume 100 times greater than roots alone. However, intensive tillage physically severs hyphal networks and reduces colonization.
Brassica crops like canola, radishes, and mustard do not form mycorrhizal associations. Including them in rotations can reduce AM fungi populations for the following crop. Balancing brassica cover crops with mycorrhizal hosts like cereal rye helps maintain fungal communities.
Commercial mycorrhizal inoculants are available as seed treatments and in-furrow products. They can benefit fields with depleted populations but are less effective in soils with already healthy fungal communities.
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