Background and aims <p>Root functional traits regulate nutrient acquisition and yield formation in legumes, yet their mechanistic role in integrating agronomic management with phosphorus (P) availability under field conditions remains poorly understood. We tested whether sowing time and tillage modify root functional traits and nodulation, thereby regulating nutrient uptake, productivity, and post-harvest soil fertility of field pea (<i>Pisum sativum</i> L.) in post-rice systems.</p> Methods <p>A two-year field experiment in eastern India used a split–split plot design with sowing time (early, delayed), tillage (relay cropping, zero tillage, conventional tillage), and P supply (20, 40, 60&#xa0;kg P ha⁻¹). Root nodulation and root traits, biomass, nutrient uptake, yield, and post-harvest soil nutrients were measured. Linear mixed-effects models, multivariate analyses, and structural equation modelling (SEM) were applied to resolve direct and trait-mediated plant–soil interaction pathways.</p> Results <p>Early sowing with conservation-oriented tillage significantly increased seed yield, biomass, and nutrient uptake, particularly at higher P supply. Yield responses were primarily mediated by enhanced nodulation and root biomass, whereas architectural traits contributed weakly. SEM identified a latent root functional efficiency axis that strongly promoted nutrient uptake, which exerted a dominant positive effect on yield, explaining &gt; 95% of yield variation. Conservation-oriented practices also improved post-harvest soil nutrient availability.</p> Conclusion <p>Nodulation and root biomass represent dominant functional pathways linking agronomic management and P availability to nutrient uptake and yield in field pea. Early sowing combined with conservation tillage and adequate P supply enhances productivity while sustaining soil fertility, providing mechanistic guidance for post-rice legume intensification.</p>