Biological nitrogen fixation of legumes crops under organic farming as driven by cropping management: A review

Abstract

CONTEXTOrganic agriculture is widely acknowledged as a strategy to reduce the environmental impacts of food production while helping achieving global climate and biodiversity targets. Yet, recent global studies and meta-analyses have highlighted the strong nitrogen (N) limitation of many organic cropping systems. Sustaining crop yields thanks to biological N fixation (BNF) in organic cropping systems is key. However, we lack a systematic estimate of BNF operated by legume crops under organic management, and how it varies according to crop species and cropping practices. OBJECTIVEThe objective of this study was to provide systematic estimate of the BNF operated by legume crops for organically managed leguminous crops according to different cropping practices. METHODSWe performed a systematic review of the literature by collecting information on the N2 fixation under organic farming – mainly as N2 fixation absolute value (Ndfa, in kgN. ha−1 yr−1) and as the percentage of above-ground biomass N derived from the atmosphere (%Ndfa). RESULTS AND CONCLUSIONWe show that significant differences exist in the BNF among crop types and cropping practices. Best performances were found for both fodder crop species compared to pulses and for crop species characterized by long growing periods. We show a strong positive relationship between Ndfa and above-ground biomass production. We also found a strong variability in the performances of single crop species and cropping practices within different geographical sites. SIGNIFICANCEThe BNF estimates provided here are key for designing more agroecological organic cropping systems that better rely on the BNF service provided by legume crops. They also represent an important base for exploring strategies that enhance N sourcing in organic cropping systems.