Can cover crops replace fertilizer completely?
Written by
Paul Reynolds
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.Legume cover crops, while likely to fix huge amounts of nitrogen, rarely supply full nutrition replacement for high-nutrient-demanding crops. Such as corn and tomatoes. All fields will require supplemental organic inputs (20-40%) to achieve complete nutrition. I have tried this on several soils and found that legume cover crops alone can only satisfy 60-80% of standard nitrogen needs.
Legume Limitations
- Hairy vetch provides 100-150 lb N/acre (45-68 kg/ha)
- Satisfies only 60-80% of corn's nitrogen needs
- Release timing doesn't always match cash crop demands
Supplementation Needs
- Heavy feeders require additional nitrogen sources
- Compost applications fill seasonal nutrient gaps
- Fish emulsion provides quick-release nitrogen boosts
Balanced Approach
- Combine legumes with non-legume covers like rye
- Layer quick-release and slow-release nutrient sources
- Test soil annually to adjust inputs precisely
Optimize N benefits through deliberate combinations. Hairy vetch can be paired with cereal rye to achieve both nitrogen fixation and biomass production. Cereal rye can hold nitrogen, preventing nitrogen leaching, and hairy vetch can fix it. I have reduced fertilizer rates up to 30% with these types of combinations compared to legumes alone.
The timing of termination is critical for nitrogen availability. Terminate legumes at flowering, which is when nitrogen fixation is maximized. This ensures nutrient availability is in line with cash crop uptake. I take weekly soil samples after termination to measure nitrogen mineralization rates, which allows for ideal timing of planting.
Cover crops do not completely replace fertilizers, but they significantly reduce the need for fertilizers. My records indicate a 40-60% reduction in fertilizer use after three years of cover cropping every season. Cover crop use saves money and builds soil health, allowing nutrients to become naturally available over time.
Read the full article: 10 Best Cover Crops for Soil Health and Yield
