Fields with no recent legume cultivation have sufficient nitrogen-fixing rhizobia for crops of faba bean (Vicia faba L.)

Marta Maluk,Cathy Hawes,Genet Gebre Yohannes,Richard S Quilliam,Francesc Ferrando-Molina,Euan K James,Adrian Langarica-Fuentes,Laura Lopez Del Egido,Geoffrey R Squire,J Peter W Young,Mark W Young,Peter Martin,Graham S Begg,Richard Gantlett,Greg Kenicer,Pietro P M Iannetta

doi:10.1007/s11104-021-05246-8

Abstract

Purpose(1) To assess the biological N fixation (BNF) potential of varieties of faba bean (Vicia faba L.) cropped with or without compost in an experimental field-scale rotation with no recent history of legumes, (2) to enumerate soil populations of Rhizobium leguminosarum sv. viciae (Rlv), and to genetically characterize the nodulating Rlv strains, (3) compare BNF with other sites in Britain.MethodsBNF was evaluated from 2012 to 2015 using 15 N natural abundance. Treatments were either PK fertilizer or compost. Soil rhizobial populations were determined using qPCR, the symbiotic rhizobia genotyped (16 S rRNA, nodA and nodD genes), and their BNF capacity assessed ex situ. The reliance of legumes on BNF at other British sites was estimated in a single season, and their nodulating symbionts examined.ResultsFaba bean obtained most of its N through BNF (>80%) regardless of variety or year. N-accumulation by cvs Babylon and Boxer increased with compost treatment in 2014/2015. Rhizobial populations were c. 105-106Rlv cells g−1 soil regardless of field or treatment. 157 Rlv microsymbionts grouped into two large nodAD clades; one mainly from V. faba, and the other from various legumes. All isolates nodulated, and some performed better than commercial inoculant strains.ConclusionsFaba bean can provide most of its nitrogen through BNF and leave economically valuable residual N for subsequent crops. Recent legume cropping in northern Europe is not essential for effective nodulation: rhizobia may persist in a range of farmland locations. Nevertheless, there is the potential to apply elite rhizobial strains as inoculants in some soils.

Highlights

Nodulated legumes are the largest contributors of biologically fixed nitrogen (N) to both natural terrestrial and agricultural environments and are a key component of sustainable agriculture (Cleveland et al 1999; Jensen et al 2012; Peoples et al 2009; Udvardi et al 2021; Unkovich et al 2008)
Recent legume cropping in northern Europe is not essential for effective nodulation: rhizobia may persist in a range of farmland locations
Abbreviations Rlv Rhizobium leguminosarum sv. viciae CSC Centre for Sustainable Cropping qPCR quantitative Polymerase Chain Reaction biological N fixation (BNF) Biological Nitrogen Fixation greenhouse gases (GHG) Greenhouse gases %Ndfa Proportion of Nitrogen derived from air bp base pair REML Restricted Maximum Likelihood SDW Sterile Distilled Water

Summary

Introduction

Nodulated legumes are the largest contributors of biologically fixed nitrogen (N) to both natural terrestrial and agricultural environments and are a key component of sustainable agriculture (Cleveland et al 1999; Jensen et al 2012; Peoples et al 2009; Udvardi et al 2021; Unkovich et al 2008). The root nodulating symbioses that they form with a diverse range of soil bacteria, collectively termed “rhizobia” (De Meyer et al 2011; Gyaneshwar et al 2011; Peix et al 2015), are capable of fixing more than 200 kg N ha-1 yr-1 in agricultural systems in both tropical (Alves et al 2003) and temperate regions (Carlsson and Huss-Danell 2003; Iannetta et al 2016; Jensen et al 2010).

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