Legumes play a key role in the sustainable intensification of agricultural systems, improving biodiversity, ecosystem services, and reducing the dependency of food production on nitrogen (N) fertilizers. This review aims to: (i) quantify seed yield per kg of total aboveground N and fixed aboveground N, (ii) study the N derived from the atmosphere (Ndfa) (as the slope of fixed aboveground N-to-total aboveground N relationship) and its potential, and (iii) estimate the partial N balance and the impact of belowground N on the net contribution of fixed N after seed harvest. We retrieved 83 studies (n = 889 data points) investigating biological N fixation, spanning from 1982 to 2020, and focusing on blue lupin (Lupinus angustifolius L.), chickpea (Cicer arietinum L.), common bean (Phaseolus vulgaris L.), cowpea (Vigna unguiculata (L.) Walp), faba bean (Vicia faba L.), field pea (Pisum sativum L.), groundnut (Arachis hypogaea L.), lentil (Lens culinaris Medik) and white lupin (Lupinus albus L.). The overall Ndfa did not change across legumes (0.84 kg fixed aboveground N kg total aboveground N^-1), except for common bean (0.57 kg fixed aboveground N kg total aboveground N^-1). In addition, common bean showed the lowest potential for the Ndfa (0.95 quantile slope), with the largest N-gap between potential and mean N fixation (0.5 quantile slope). The straw N concentration (r² = 0.47) was the main contributor to the variation in the partial N balance. The incorporation of the belowground N to estimate overall N balance showed that this fraction is a key component to study the role of legumes in maintaining soil N fertility in agricultural systems. Future studies should accurately quantify both above- and below-ground contribution to N fixation process in order to improve the estimation of field N balances in legume-based systems.

豆类在农业系统的可持续集约化、改善生物多样性、生态系统服务以及减少粮食生产对氮 (N) 肥料的依赖方面发挥着关键作用。本综述旨在：（i）量化每公斤地上总氮和固定地上氮的种子产量，（ii）研究来自大气的氮（Ndfa）（作为固定地上氮与地上总氮关系的斜率） ）及其潜力，以及（iii）估计部分氮平衡和地下氮对种子收获后固定氮的净贡献的影响。我们检索了 83 项研究（n = 889 个数据点）调查生物固氮作用，时间跨度从 1982 年到 2020 年，重点关注蓝羽扇豆 ( Lupinus angustifolius L.)、鹰嘴豆 ( Cicer arietinum L.)、菜豆 (Phaseolus vulgaris L.)、豇豆 ( Vigna unguiculata (L.) Walp)、蚕豆 ( Vicia faba L.)、豌豆 ( Pisum sativum L.)、落花生 ( Arachis hypogaea L.)、小扁豆 ( Lens culinaris Medik) 和白羽扇豆（Lupinus albus L.）。豆科植物的总体 Ndfa 没有变化（0.84 kg 固定地上 N kg 总地上 N ^-1），除了普通豆（0.57 kg 固定地上 N kg 总地上 N ^-1）。此外，普通豆的 Ndfa 潜力最低（0.95 分位数斜率），潜力和平均 N 固定之间的 N 间隙最大（0.5 分位数斜率）。秸秆氮浓度（r ²= 0.47）是部分 N 平衡变化的主要贡献者。结合地下氮来估计总体氮平衡表明，该部分是研究豆科植物在农业系统中维持土壤氮肥力作用的关键组成部分。未来的研究应准确量化地上和地下对固氮过程的贡献，以改进豆科植物系统中田间氮平衡的估计。