One of the most significant ecosystem services (ES) provided by legumes in arable systems is biological nitrogen fixation (BNF), contributing to nitrogen (N) provision for subsequent crops. However, this service is often undervalued or broadly generalized across regions and species, leading to potential over-fertilization and underestimation of legume contributions.
This pilot study focuses on developing and testing simple, site-specific indicators (ESI) that reflect the true N provision of legumes under varied species, variety, climate, and soil conditions. These indicators aim to inform farmers, advisors, and regulators, enabling more precise nitrogen management, improved profitability, and reduced environmental risks.
Specific objectives are:
- Compare post-legume nitrogen status (FSNS) and nitrogen replacement values (NRV) across different grain legume species and varieties within sites.
- Assess whether legume species and variety differences require site-specific monitoring rather than broad extrapolation.
- Investigate if N balance estimates differ significantly between legume crops and cropping systems.
- Across sites, assess the relationships between FSNS/NRV and potential N provision indicators, such as legume yield, biomass, harvest index (HI), and following crop soil mineral nitrogen (SMN).
- Determine if yield, biomass, or HI are reliable proxies for NRV, and perform sensitivity analysis using FSNS as the benchmark.
- Evaluate whether remote sensing tools (e.g., spectral reflectance, crop N status sensors) can effectively differentiate N status in wheat following different legumes.
- Explore additional ES benefits and test the practicality of monitoring tools across regions.
- Evaluate simple BNF indicators like nodule count and colour, and test their relevance under varied climates.
- Collect metadata for LCA (Life Cycle Assessment) and economic modeling, including soya replacement potential.
- If resources allow, use 15N methods to quantify BNF variability across species and conditions.
- Trial monitoring tools for other ES indicators, such as pollinator provision, soil health (e.g. VESS, earthworm counts), and green cover using tools like Canopeo.
This trial series will contribute to the development of simplified, practical methodologies for assessing nitrogen-related ecosystem services by legumes, helping stakeholders make informed decisions at the field level across diverse European agroecosystems.