Fallow syndrome in corn is primarily caused by a significant reduction in Vesicular Arbuscular Mycorrhizal Fungi (VAM) populations in the soil. This typically occurs when a field is left unplanted (fallow) or planted with non-host crops for an extended period.
Why Corn needs Vesicular Arbuscular Mycorrhizal Fungi (VAM)
- Corn Utilizes a Symbiotic Relationship with VAM:
- Corn relies on VAM to assist in the uptake of immobile nutrients, particularly phosphorus (P) and zinc (Zn)
- On corn roots, the fungi extend their hyphae into the soil, effectively increasing the surface area of the root system
- VAM requires a living host plant to survive and reproduce.
- When no host plants are present (during a fallow year) or when non-mycorrhizal crops (brassicas or sugar beets) are grown, the existing network of VAM dies off.
- Low VAM levels prevent young plants from accessing sufficient phosphorus, even if soil test levels indicate P is adequate.
Fallow Syndrome Symptoms in Corn
- Stunting: Slow early-season growth.
- Purple Leaves: A classic sign of phosphorus deficiency.
- Interveinal Chlorosis: Signs of zinc deficiency.
- Poor Root Development: Smaller, less branched root systems.
What Can Cause Fallow Corn Syndrome
- Fallow Ground: No host plants for VAM to survive on.
- Flooting: Extended periods of saturated soil (prevented planting) can kill off VAM populations due to anaerobic conditions.
- Non-Host Crops: Planting brassicas (radish, cabbage) or Chenopodiaceae (sugar beets) does not support VAM, leading to a similar effect as bare fallow.
- Soil Disturbance: Excessive tillage can physically disrupt the remaining mycorrhizal networks.
Ways to Reduce Fallow Syndrome Risk
- Starter Fertilizer: Applying high rates of banded phosphorus (and zinc) near the seed at planting can help the plant bypass the need for VAM in early growth stages.
- Cover Crops: Planting mycorrhizal-friendly cover crops (like oats, cereal rye, or wheat) during fallow periods maintains the fungal population.
- Reduced Tillage: Minimizing soil disturbance helps preserve existing fungal structures.
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| Figure 2. The corn to the left was prevent plant the prior year that had a cover crop of turnips planted in late summer; The corn to the right was planted to soybeans the prior season. Source - Syngenta |
For additional guidance on crop rotation, cover crop selection, and fertility strategies, consult your local agronomy advisor or seed specialist.
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