Speaker
Description
Introduction
Grain legumes (pulses) are interesting parts in sustainable crop rotations due to their ability of biologic nitrogen fixation (BNF). Among them, faba bean has a huge potential to derive nitrogen (N) from the atmosphere (Walley et al. 2007; Liu et al. 2019; Palmero et al. 2022). However, empirical results suggest that they are mostly N self-sufficient when balancing only the aboveground contribution. Throughout the literature there are often cited estimations of large additional N contribution from the belowground part (belowground factor ~1.4). This mostly switches the N balance of faba bean from negative/neutral to surplus in contrast to only accounting the aboveground part, with consequences for the evaluation of rotational effects and/or risk of losses. We critically revised this popular belowground factor and derived an updated yield-based BNF estimation for faba bean.
Materials & Methods
Two datasets were compiled from previously published literature between 1966 and 2023: (1) for assessing the relation of belowground N to total plant N from 42 values reported in 14 primary studies (field and greenhouse experiments) and (2) for assessing the relationship between seed yield and BNF from >300 values reported in 51 primary studies. From this comprehensive data we derived a new belowground factor) and an estimation of seed yield based BNF (aboveground only as well as total including belowground contribution). As a case study this newly derived functions were used to calculate N fixation and N balances from German national statistics data in comparison to the legal framework (German ordinance on nutrient-flow balances, StoffBilV 2017)
Results & Discussion
A critical review of the commonly used belowground factor (1.4) based on our empirical relation between belowground and aboveground N in faba bean plant material reveals a previous overestimation and leads to a smaller factor of 1.15. Applying this new belowground factor together with our comprehensive dataset 2 we found a mean N fixation of 49 kg per Mg faba been seed yield. In terms of N balances, a minimum fixation of 135 kg (2.76 Mg dry matter seed yield) is needed to reach a surplus. Compared to previously derived functional relationships, this assessment is much lower than other results including belowground contributions (Unkovich et al. 2010; Anglade et al. 2015; Palmero et al. 2022). Compared to the legal framework our functional relation results in 15% lower estimations of N fixation and 50% lower N balances from faba bean cultivation across Germany (1999-2023). This leads to a considerable different valuation of faba bean pre-crop and rotational effects in European cropping systems.
References
Anglade J, Billen G, Garnier J (2015) Relationships for estimating N2 fixation in legumes: Incidence for N balance of legume-based cropping systems in europe. Ecosphere 6:1–24. https://doi.org/10.1890/ES14-00353.1
Liu L, Knight JD, Lemke RL, Farrell RE (2019) A side-by-side comparison of biological nitrogen fixation and yield of four legume crops. Plant Soil 442:169–182. https://doi.org/10.1007/s11104-019-04167-x
Palmero F, Fernandez JA, Garcia FO, et al (2022) A quantitative review into the contributions of biological nitrogen fixation to agricultural systems by grain legumes. Eur J Agron 136:126514. https://doi.org/10.1016/j.eja.2022.126514
StoffBilV (2017) Verordnung über den Umgang mit Nährstoffen im Betrieb und betriebliche Stoffstrombilanzen (Stoffstrombilanzverordnung - StoffBilV) vom 14.12.2017. BGBl I 3942
Unkovich MJ, Baldock J, Peoples MB (2010) Prospects and problems of simple linear models for estimating symbiotic N2 fixation by crop and pasture legumes. Plant Soil 329:75–89. https://doi.org/10.1007/s11104-009-0136-5
Walley FL, Clayton GW, Miller PR, et al (2007) Nitrogen economy of pulse crop production in the Northern Great Plains. Agron J 99:1710–1718. https://doi.org/10.2134/agronj2006.0314s
| Keywords | N2 fixation; legumes; pulses; cropping systems; crop rotation |
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