Summary
This two-year organic field trial examined how cover crop type and biomass production predict nitrogen fertiliser replacement value in cereal rotations. The researchers found that legume-containing mixtures (particularly red clover and three-way mixtures) achieved NFRV up to 100 kg N ha⁻¹, with strong correlation (r = 0.83 in autumn) between cover crop biomass and subsequent nitrogen availability to the test crop. A critical threshold of 1 Mg DM ha⁻¹ autumn biomass was identified; cover crops below this level provided negative residual nitrogen effects.
Regional applicability
The study was conducted in a European organic field system and is directly applicable to United Kingdom organic cereal production under temperate conditions. The use of spring barley and typical UK cover crop species (ryegrass, plantain, red clover) makes findings transferable to UK farming practice, though local soil conditions and seasonal weather variability may affect achievable biomass levels.
Key measures
Aboveground biomass (Mg ha⁻¹), biomass nitrogen yield (kg N ha⁻¹), nitrogen fertiliser replacement value (kg N ha⁻¹ equivalent), spring barley grain yield, soil mineral nitrogen
Outcomes reported
The study quantified nitrogen fertiliser replacement value (NFRV) of five cover crop types and measured their aboveground biomass and biomass nitrogen yield in autumn and spring. It identified a strong positive correlation between cover crop autumn biomass and NFRV, establishing a 1 Mg DM ha⁻¹ threshold below which NFRV becomes negative.
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